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Chemical transformation of toxic metals by a Pseudomonas strain from a toxic waste site
Abstract
Pseudomonas maltophilia strain O-2, isolated from soil at a toxic waste site in Oak Ridge, Tennessee, catalyzed the transformation and precipitation of numerous toxic metal cations and oxyanions. When a viable inoculum (1%) of O-2 was introduced into nutrient broth containing Hg(II), Cr(VI), Se(IV), Pb(II), Au(III), Cd(II), Te(IV), or Ag(I), effective removal of the toxic metal was complete within 1, 1, 2, 2, 2, 4, 5, and 7 d, respectively. The NADPH-dependent reduction of Hg(II) to Hg0 was catalyzed by an inducible mercuric reductase. The reduction of selenite and tellurite to their insoluble elemental forms appeared to be mediated by an intracellular glutathione reductase that utilized the spontaneously formed bis(glutathio)Se(II) or bis(glutathio)Te(II), respectively, as pseudosubstrates. The three-electron reduction of hexavalent chromium was catalyzed by a membrane-bound chromate reductase. The enzymatic basis for the remaining metal transformations was not immediately apparent. It is anticipated that Pseudomonas maltophilia and related organisms could eventually be exploited for the removal of toxic metal wastes from selected, heavily polluted sites.
... The plant growth promoting rhizobacteria (PGPR) colonize the roots of plants following inoculation onto seed and enhance plant growth through fixation of atmospheric nitrogen, production of siderophores that chelate iron and make it available to the plant root, solubilization of minerals such as phosphorus and synthesis of phytohormones (Kloepper and Schroth, 1978). Blake et al. (1993) reported that Xanthomonas maltophyla was shown to catalyze the reduction and precipitation of Cr 6+ to Cr 3+ , a significant less mobile and environmentally less hazardous compound. The same strain was also found to induce the transformation of other toxic metal ions including Pb 2+ and Hg 2+ . ...
... Solubilization of metals by rhizobacteria was reported by Zhuang et al. (2007), which resulted in increased accumulation of Ni by Alyssum murale. The results obtained in present study are in agreement with Blake et al. (1993), Diaz et al. (1996), Weng et al. (2004), Citterio et al. (2005), Madhaiyan et al. (2007) and Arora and Sharma (2009). ...
... Significant reduction in total and DTPA extractable trace metals by microbial inoculation may be attributed to their increased uptake by mustard and maize. Similar results are reported by Blake et al. (1993), Diaz et al. (1996), Citterio et al. (2005), Weng et al. (2004), Madhaiyan et al. (2007) and Arora and Sharma (2009). However, reduction in DTPA extractable trace metal due to application of vermicompost, lime and lime + vermicompost may be attributed to formation of insoluble precipitates, complexation or adsorption. ...
Accumulation of trace metals and their bio-availability in soils is likely to have for reacting consequences on soil health as well as growth, yield and quality of crops. To assess the extent of trace metal contamination, soil and plant samples were collected from farmers fields around Patratu Thermal Power Station, Patratu, Kathara and Gobindpur Project CCL, Bokaro and waste disposal site, Jamshedpur. Analysis of soil pH, electrical conductivity and organic carbon content revealed that soils collected from Patratu were moderately acidic in soil reaction. Soil reaction in case of Bokaro and Jamshedpur ranged from acidic to neutral or alkaline. The electrical conductivity was within the safe limit, while the organic carbon content was medium to high. The soils were low in available N and P, while low to medium in available K status. Available micronutrients were above the critical value. DTPA-Cd was detected in 50 per cent soil samples of Patratu, 45 per cent of Bokaro and 80 per cent of Jamshedpur. All soil samples from Patratu and nearly 50 per cent samples of Bokaro and Jamshedpur contained high DTPA extractable Pb, Ni and Co. The mean value of total Cd, Pb, Ni and Co in soils were 7.76, 40.41, 238.95 and 109.27 mg kg-1 in Patratu, 8.70, 158.60, 242.45 and 218.40 mg kg-1 in soils of Bokaro and 17.50, 126.40, 143.05 and 333.10 mg kg-1 in soils of Jamshedpur. Increasing trend in soil pH with depth was observed while EC, OC, available N, P, K, micronutrients, Pb and Ni decreased with depth in each pedon. High Cd content in subsurface horizon compared to surface horizon was noticed in all pedons. Total trace metal content in soil profile collected from Patratu, Bokaro and Jamshedpur indicated that surface horizon contained comparatively high Zn and Cu, however, no definite trend for Mn and Fe was noticed. Higher Cd and Ni were recorded in soils of Jamshedpur while higher Pb and Co in soils were detected in Patratu. The plant samples collected from farmers field of Patratu had Cd ranging from traces to 34.50 mg kg-1 (guava leaves), Pb from traces to 11.45 mg kg-1 (palash leaves), Ni from 4.20 (maize and akwan leaves) to 36.00 mg kg-1 (palash leaves) and Co from traces to 39.85 mg kg-1 (palash leaves). Vegetable crops contained higher amount of trace metals particularly Cd, Pb, Ni and Co, which were nearer or above the tolerance level. Cadmium content of 75 per cent plant samples, Pb content of 58 per cent samples and Co content of all samples found to be above the MTL (Cd – 3, Pb – 10, Ni – 50 and Co – 5 mg kg-1).
Farmers’ field trial was conducted at Patratu (Ramgarh) to study the effect of lime, compost, plant growth promoting rhizobacteria and arbuscular mycorrhizal fungi for remediation of high trace metal levels in mustard-maize cropping system. Results revealed that inoculation with Glomus mossae + vermicompost @ 2.5 t ha-1 significantly increased the grain yield of mustard (1.26 t ha-1), maize (6.72 t ha-1) and system (9.65 t ha-1) and the extent was 10, 25 and 20 per cent, respectively as compared to control. Inoculation of Pseudomonas striata + vermicompost @ 2.5 t ha-1 recorded significantly higher N, P and K uptake by mustard and maize. Inoculation with G. mossae, P. striata and A. chroococcum increased Zn concentration to the extent 13 to 32, 10 to 24 and 9 to 24 per cent, respectively over control. Copper, manganese and iron uptake followed almost similar trend as that of Zn. Microbial inoculants with or without vermicompost increased the trace metal removal, however, vermicompost alone decreased the removal. Vermicompost, lime and lime + vermicompost significantly reduced the total Cd uptake by mustard and maize. Inoculation with Glomus mossae resulted in elevated level of Cd in mustard and maize plants. Similar observations were recorded in case of Pb and Ni uptake. Estimation of bio accumulation factors (BAFs) indicates that inoculation of Glomus mossae alone resulted in significantly high BAFs value for all trace metals. It was observed that microbial inoculations reduced the total Zn, Cu, Mn and Fe content in soil. However, available micronutrients were significantly reduced by microbial inoculation and amendments. Total trace metal content in soil was significantly reduced by microbial inoculation alone or that in combination with vermicompost. However, DTPA-extractable trace metals decreased with addition of amendments as well as inoculation of microbes. Glomus mossae was most effective in remediating the trace metals under this study, the total metal content reduced effectively by their inoculation alone while inoculation along with vermicompost resulted in reducing the DTPA-extractable fraction, more effectively. The extent of reduction in total Cd, Pb, Ni and Co after harvest of both crops was 6 to 26, 5 to 12, 6 to 15 and 1 to 4 per cent, respectively over control. However, the corresponding values observed for DTPA extractable Cd, Pb, Ni and Co was 53 to 65, 20 to 32, 24 to 34 and 18 to 30 per cent over control in microbial inoculation and 46 to 47, 14 to 17, 9 to 13 and 11 to 19 per cent in case of amendments.
... The specific activity of chromate reductase ranged between 0.2356 to 0.8362 and 0.314 to 6457 μmol Cr(VI) reduced/min/mg protein in the cell lysate and supernatants fraction respectively. Our results contrast with those reported by Blake [55], Some number of methods focused on transforming Cr(VI) into Cr(III) have been used to decrease the toxicity of media containing Cr(VI). Chemical methods, including adding lime, coagulation, ion exchange, membrane separation, and adsorption followed by chemical precipitation as Cr(OH) 3 , have conventionally been used [44,45]. ...
... The specific activity of chromate reductase ranged between 0.2356 to 0.8362 and 0.314 to 6457 µmol Cr(VI) reduced/min/mg protein in the cell lysate and supernatants fraction respectively. Our results contrast with those reported by Blake [55], who determined that the reduction of Cr(VI) in S. maltophilia was due to the activity of a membrane-associated reductase enzyme, which is expressed constitutively. ...
An Gram negative strain of S. maltophilia, indigenous to environments contaminated by Cr(VI) and identified by biochemical methods and 16S rRNA gene analysis, reduced chromate by 100%, 98-99% and 92% at concentrations in the 10-70, 80-300, and 500 mg/L range, respectively at pH 7 and temperature 37 °C. Increasing concentrations of Cr(VI) in the medium lowered the growth rate but could not be directly correlated with the amount of Cr(VI) reduced. The strain also exhibited multiple resistance to antibiotics and tolerance and resistance to various heavy metals (Ni, Zn and Cu), with the exception of Hg. Hexavalent chromium reduction was mainly associated with the soluble fraction of the cell evaluated with crude cell-free extracts. A protein of molecular weight around 25 kDa was detected on SDS-PAGE gel depending on the concentration of hexavalent chromium in the medium (0, 100 and 500 mg/L). In silico analysis in this contribution, revealed the presence of the chromate reductase gene ChrR in S. maltophilia, evidenced through a fragment of around 468 bp obtained experimentally. High Cr(VI) concentration resistance and high Cr(VI) reducing ability of the strain make it a suitable candidate for bioremediation.
... The specific activity of chromate reductase ranged between 0.2356 to 0.8362 and 0.314 to 6457 μmol Cr(VI) reduced/min/mg protein in the cell lysate and supernatants fraction respectively. Our results contrast with those reported by Blake [55], Some number of methods focused on transforming Cr(VI) into Cr(III) have been used to decrease the toxicity of media containing Cr(VI). Chemical methods, including adding lime, coagulation, ion exchange, membrane separation, and adsorption followed by chemical precipitation as Cr(OH) 3 , have conventionally been used [44,45]. ...
... The specific activity of chromate reductase ranged between 0.2356 to 0.8362 and 0.314 to 6457 µmol Cr(VI) reduced/min/mg protein in the cell lysate and supernatants fraction respectively. Our results contrast with those reported by Blake [55], who determined that the reduction of Cr(VI) in S. maltophilia was due to the activity of a membrane-associated reductase enzyme, which is expressed constitutively. ...
An Gram negative strain of S. maltophilia, indigenous to environments contaminated by Cr(VI) and identified by biochemical methods and 16S rRNA gene analysis, reduced chromate by 100%, 98–99% and 92% at concentrations in the 10–70, 80–300, and 500 mg/L range, respectively at pH 7 and temperature 37 °C. Increasing concentrations of Cr(VI) in the medium lowered the growth rate but could not be directly correlated with the amount of Cr(VI) reduced. The strain also exhibited multiple resistance to antibiotics and tolerance and resistance to various heavy metals (Ni, Zn and Cu), with the exception of Hg. Hexavalent chromium reduction was mainly associated with the soluble fraction of the cell evaluated with crude cell-free extracts. A protein of molecular weight around 25 kDa was detected on SDS-PAGE gel depending on the concentration of hexavalent chromium in the medium (0, 100 and 500 mg/L). In silico analysis in this contribution, revealed the presence of the chromate reductase gene ChrR in S. maltophilia, evidenced through a fragment of around 468 bp obtained experimentally. High Cr(VI) concentration resistance and high Cr(VI) reducing ability of the strain make it a suitable candidate for bioremediation.
... Selenite reduction in Rhodospirillum rubrum, Rhodobacter capsulatus, Escherichia coli, and Bacillus subtilis is in response to reduced thiols in the cytoplasm (Garbisu et al. 1999;Kessi and Hanselmann 2004;Kessi 2006). Reduction of selenite to Se 0 by Pseudomonas (now classified as Stenotrophomonas) maltophilia strain 0-2 was reported to be mediated by glutathione since butionine sulfoximine, an inhibitor of c-glutamylcysteine synthetase, prevents the synthesis of glutathione and, thereby, increases bacterial sensitivity to selenite (Blake et al. 1993). Selenite induces the production of thioredoxin in Bacillus subtilis which is considered to facilitate the formation of Se 0 (Garbisu et al. 1996). ...
... Selenite was responsible for altered cell morphology which was reported for Clostridium pasteurianum (Laishley et al. 1980), Wolinella succinogenes (Tomei et al. 1992), Desulfovibrio desulfuricans DSM 1924 (Tomei et al. 1995), hydrothermal vent bacteria (Rathgeber et al. 2002), Rhodobacter sphaeroides (Bebien et al. 2001), and Pseudomonas strain CA5 (Hunter and Manter 2009). Cell lysis was observed when Wolinella succinogenes (Tomei et al. 1992) and Stenotrophomonas (formerly Pseudomonas) maltophilia (Blake et al. 1993) were grown in the presence of selenite. Cell lysis could be attributed to the production of highly destructive ROS such as superoxide anion (O 2 − ) released following the reaction of reduced thiols with selenite (Kramer and Ames 1988;Zannoni et al. 2008). ...
Selenium (Se) is transformed by phylogenetically diverse bacteria following several basic strategies which include: (1) satisfying a trace element requirement for bacterial synthetic machinery (assimilatory metabolism), (2) cellular energy production coupled to oxidation/reduction reactions (dissimilatory metabolism), and (3) detoxification processes. Some bacteria can use Se for respiration under limiting anaerobic conditions, generating energy to sustain growth. Under aerobic conditions, Se behaves as a toxicant and bacteria have evolved different strategies to counteract it. An important detoxification mechanism involves the formation of Se nanoparticles with a diminished toxic potential, but the cells have to properly manage these products in order to maintain their integrity. The bacterial metabolism of Se can be regarded as a survival mechanism when Se compounds prove to be highly toxic. Secondly, selenium is used to obtain energy in a nutrient-depleted environment, therefore allowing to specialized bacterial species to prevail over competitors that cannot exploit this resource. To achieve the Se metabolic activities, numerous unique enzymes are employed. While some enzymes have been isolated and are markedly specific for Se, many of the Se enzymes remain to be isolated. The formation of Se nanoparticles inside bacteria and the transportation mechanisms to the extracellular environment are still under debate. Se nanoparticles do not appear to play a nutritional (energy storage) or ecological function for bacteria, being by-products of bacterial metabolism. However, from a biotechnological standpoint, these conversions could be used to (1) clean up industrial effluents rich in Se and (2) to produce biomaterials with industrial applications (biofactory).
... The reduction of selenite by a strain of Pseudomonas has been proposed to proceed according to mechanism indicated in reactions (6) -(10) [12]. ...
... TEM results indicate (Se, S) particles and amorphous FeS precipitates (Figure 1(b)). The (Se, S) particles become crystalline and more Se-rich ( and (12) The Desulfovibrio desulfuricans bacterium is able to enrich Se in the (Se, S) solid solution particles. The process also results in the transformation from amorphous (Se, S) particles to polycrystalline Se particles. ...
As determined by transmission electron microscopy (TEM), the reduction of selenate and selenite by Desulfovibrio desulfuricans, a sulfate-reducing bacterium, produces spherical (Se, S) sub-micro particles outside the cell. The particles are crystalline or amorphous, depending on medium composition. Amorphous-like Se-rich spherical particles may also occur inside the bacterial cells. The bacteria are more active in the reduction of selenite than selenate. The Desulfovibrio desulfuricans bacterium is able to extract S in the (S, Se) solid solution particles and transform S-rich particles into Se-rich and Se crystals. Photoautotrophs, such as Chromatium spp., are able to oxidize sulfide (S 2− ). When the bacteria grow in sulfide- and selenide-bearing environments, they produce amorphous-like (S, Se) globules inside the cells. TEM results show that compositional zonation in the (S, Se) globules occur in Chromatium spp. collected from a top sediment layer of a Se-contaminated pond. S 2− may be from the products of sulfate-reducing bacteria. Both the sulfate-reducing bacteria and photosynthetic Chromatium metabolize S preferentially over Se. It is proposed that the S-rich zones are formed during photosynthesis (day) period, and the Se-rich zones are formed during respiration active (night) period. The results indicate that both Desulfovibrio desulfuricans and Chromatium spp. are able to immobilize the oxidized selenium (selenate and/or selenite) in the forms of elemental selenium and (Se, S) solid solutions. The bacteria reduce S in the (Se, S) particles and further enrich Se in the crystalline particles. The reduced S combines with Fe 2+ to form amorphous FeS.
... Fast can alter metal bacterial transformations bioavailability in soil. For example, a strain of the bacterium Xanthomonas maltophyla can be exposed to catalyze the reduction and precipitation of highly mobile Cr ions from far less mobile and environmentally less dangerous substances (Blake et al., 1993). Some strains of bacteria have been reported to have induced transformations of hazardous metal ions such as Pb 2+ , Hg 2+ , Au 3+ , Te 4+ , and Ag + (Lasat, 2002). ...
Nutrient recycling from soil to fauna is determined by the flora for maintaining an ideal food chain and ecological balance which is solely dependent on nutrient availability and uptake from soils in an optimum quantity after maintaining specific physiological pathways. Some soil physicochemical properties and excess availability of nonessential metals and metalloids limit the availability of essential nutrients uptake by plants though some metals and metalloids are essential for plants. Excess quantity of nonessential metals and metalloids into the food chain via plant uptake enhances threats to environment, human, and other animal’s health though plants body have own strategy to maintain homeostatic balance upon excess uptake of metals and metalloids for their perpetuation. There are several sources of metals and metalloids including parent materials (lithogenic source) and anthropogenic sources (industries) responsible for affecting both agricultural and urban soils. Though excess metals and metalloids can reduce the function, occurrence, and diversity of some microorganisms as well as impede organic matter decomposition and mineralization of nutrients, microorganisms can play a satisfactory role in reducing phytotoxicity by applying several remediation strategies. On the other hand, changes in structures (installation of ETP-effluent treatment plant), incorporation of strict regulation scanner for industries, and particularly phytoremediation strategies have positive results for reducing metals and metalloids sequestration in soils. However, plants face oxidative stress or even the death penalty when grown in metals and metalloids contaminated soils. There are proven phytoremediation properties of (>400 hyperaccumulator) plant species and those should be exploited for developing phytoremediation-based sustainable mitigation strategies against metals and metalloids polluted soils. The chapter highlights the microorganisms and phytoremediation based mitigation strategies of plants against metals and metalloids polluted soils.
... Several studies have demonstrated the involvement of beneficial micro-organisms, such as rhizobacteria or endophytes associated with plant roots, for the extraction or accumulation of elements of interest or for reducing toxicity and the immobilization of elements in soil [13]. Pseudomonas maltophilia was reported to have reduced the toxicity of chromium (Cr) in soils by reducing the toxic Cr 6+ to nontoxic and immobile Cr 3+ and to have restricted the mobility of toxic ions like cadmium (Cd 2+ ), lead (Pb 2+ ), and mercury (Hg 2+ ) [13,22,23]. Rajkumar and Freitas [24] also observed that the inoculation of Ricinus communis with Pseudomonas sp. ...
Bioaugmentation promises benefits for agricultural production as well as for remediation and phytomining approaches. Thus, this study investigated the effect of soil inoculation with the commercially available product RhizoVital®42, which contains Bacillus amyloliquefaciens FZB42, on nutrient uptake and plant biomass production as well as on the phytoaccumulation of potentially toxic elements, germanium, and rare earth elements (REEs). Zea mays and Fagopyrum esculentum were selected as model plants, and after harvest, the element uptake was compared between plants grown on inoculated versus reference soil. The results indicate an enrichment of B. amyloliquefaciens in inoculated soils as well as no significant impact on the inherent bacterial community composition. For F. esculentum, inoculation increased the accumulation of most nutrients and As, Cu, Pb, Co, and REEs (significant for Ca, Cu, and Co with 40%, 2042%, and 383%, respectively), while it slightly decreased the uptake of Ge, Cr, and Fe. For Z. mays, soil inoculation decreased the accumulation of Cr, Pb, Co, Ge, and REEs (significant for Co with 57%) but showed an insignificant increased uptake of Cu, As, and nutrient elements. Summarily, the results suggest that bioaugmentation with B. amyloliquefaciens is safe and has the potential to enhance/reduce the phytoaccumulation of some elements and the effects of inoculation are plant specific.
... strain EA106 has been reported to significantly increase Fe plaque formation, thereby attenuating As uptake by rice roots (Lakshmanan et al., 2015). In another study, a strain of Pseudomonas maltophilio is reported to transform the mobile and toxic form of chromium (Cr(VI)) to the nontoxic and immobile form (Cr(III)) and also minimized the mobility of other toxic ions, such as Hg 21 , Pb 21 and Cd 21 (Blake et al., 1993;Park, Keyhan, & Matin, 1999). ...
Aim: The present study explores the effects of high population density (PD), climatic and environmental factors on transmission of coronavirus disease 2019 (COVID-19) in selected metropolitan cities of India.
Materials and Methods: A data extraction sheet has been prepared to summarize the data of confirmed severe acute respiratory syndrome corona virus-2 (SARS-CoV-2) cases and number of deaths in ten metropolitan cities, which was taken from Government of India website. The data on environmental factors of each selected metropolitan city were compiled from the official website and climatic conditions from Meteorological Department Government of India.
Results: In India, maximum positive COVID-19 cases (>32%) has been found in tropical wet and dry climate zone. While the incidence of COVID-19 cases has been found less in the arid zone of India. Poor correlation has been found between level of Vitamin D, total COVID-19 cases, and mortalities in the studied metropolitan cities. No significant correlation was found between the health care index and COVID-19 cases and mortality.
Conclusions: Correspondence and principal component analysis statistics showed high PD, poverty, climatic and environmental factors influenced the SARS-CoV-2 transmission in metropolitan cities of India.
... Use of Pseudomonas putida found to reduce Cd phytotoxicity in plants and enhanced accumulation (Huang and Tao 2005). Similarly, P. maltophilia reduces the mobility and toxicity of Cr 6+ , Hg, Pb and Cd (Blake et al. 1993). Escherichia coli and Moraxella sp. ...
Global modernization has increased the risk of heavy metal contaminants in our water bodies and soil system due to various anthropogenic activities. By polluting soil and water, these heavy metals get into our food cycle and subsequently increase the adverse effect on environmental and human health. The use of plants for extraction and accumulation of heavy metal from contaminated sites exhibited safe and suitable options without disturbing soil function. Plants performance is affected severely under metal stress condition which that resulted in poor plant growth and biomass production. Moreover, to improve the phytoremediation approach application of rhizospheric microbes enhances the additional benefits and effectiveness of the remediation process by transforming or detoxifying the heavy metals under low and heterogeneous metal-containing sites. In this chapter, we will cover various rhizospheric microorganisms in association with plants, mechanism followed by them to alleviate metal stress, limitation and future challenges to enhance our knowledge for their effective utilization in near future to manage metals contaminated sites more effectively.
... The reason might be that some plants may employ rhizosphere-dwelling plant growthpromoting bacteria or mycorrhizal fungus to minimize the negative effects of heavy metals and thus in uence heavy metal uptake by plants. It has been reported that a strain of Pseudomonas maltophilia has converted mobile and toxic Cr 6+ to nontoxic and immobile Cr 3+ , which also reduced the mobility of other hazardous ions such as Hg 2+ , Pb 2+ , and Cd 2+ in the context(Blake et al., 1993;Park et al., 1999). It is noteworthy that the pot culture experiment in the current study showed a reduction in metal ion availability by the application of FBBs in the form of FBB while reducing the pH in soil in comparison with FBB untreated soil (Table 2). ...
Heavy metal pollution due to excessive use of chemical fertilizers (CF) causes a major damage to the environment. Microbial consortia, closely associated with the rhizosphere are able to remediate heavy metal-contaminated soil by reducing plant toxicity. Thus, this study was undertaken to examine the remedial effects of microbial biofilms against contaminated heavy metals. Fungi and bacteria isolated from soil were screened for their tolerance against Cd ²⁺ , Pb ²⁺ and Zn ²⁺ . Fungal-bacterial biofilms (FBBs) were developed with the highest tolerant isolates and were further screened for their bioremediation capabilities against heavy metals. The best biofilm was evaluated for its rhizoremediation capability with different CF combinations using a pot experiment conducted under greenhouse conditions with potato. Three bacterial and two fungal isolates were selected to develop FBBs upon the tolerance index (TI) percentage. Significantly (P < 0.05) the highest metal removal percentage was observed in Trichoderma harzianum and Bacillus subtilis biofilm under in situ condition. The biofilm with 50% of recommended CF (50CB) significantly (P < 0.05) reduced the soil available Pb ²⁺ by 77%, Cd ²⁺ by 78% and Zn ²⁺ by 62% compared to 100% recommended CF (100C). In comparison to initial soil, it was 73%, 76% and 57% lower of Pb ²⁺ , Cd ²⁺ and Zn ²⁺ , respectively. In addition, 50CB treatment significantly (P < 0.05) reduced the metal penetration into the tuber tissues in comparison with 100C. Thus, it is concluded that T. harzianum–B. subtilis biofilm is an ideal combination to remediate soil contaminated with Cd ²⁺ , Pb ²⁺ and Zn ²⁺ .
... Additionally, Cr(VI) reported to act as an electron acceptor in the electron transport chain involved in anaerobic Cr(VI) reduction, whereas aerobic Cr(VI)-reducing bacteria consume soluble reductases in their cytosols [87,88], nevertheless some exception are there which involve the membrane-associated cell portions for Cr(VI) reduction such as Pseudomonas maltophilia strain, Bacillus megaterium strain TKW3, Amphibacillus sp. KSUCr3 [86,89,90]. Chromate reductases is a cytoplasmic flavoprotein that is broadly studied for the biochemistry of Cr(VI) reductases, which help in the reduction of Cr(VI) and Cr(III) [91,92]. ...
During the past few decades, urbanization and industrialization have leaped human culture and environment of living. Industrialization has caused the generation of various heavy metal, triggering environmental pollution. India is the top producer of chromium (Cr) in the world. Cr salts are consumed in the tannery, electroplating industry, dye industries, which leads to the release of the Cr(VI) contaminated wastewater into the water bodies and soil. Due to the toxic nature of Cr(VI), it has gained attention for remediation purposes but preexisting physical and chemical techniques are quite expensive and produce secondary waste, yet causing another issue for remediation. They also required extensive labor, still after performing extensive practice methods, these methods are not quite feasible for the Cr(VI) removal in treated effluent wastewater. Therefore, microbial remediation technique can be used for successful remediation of Cr(VI) contaminated industrial effluent wastewater before their release in the water bodies and soil. Thus, the present chapter deals with chemistry of Cr, its use, availability and its speciation, toxicity, and regulatory standards. To restore the Cr-contaminated site, the chemical/biological remediation processes for Cr(VI) and their efficiency have been summarized in some detail. The effect of Cr on various microbial isolates and their reduction capacity toward Cr(VI) are also discussed.
... The microorganisms could be able to remediate the toxicity of heavy metals through several ways, including transformation into nontoxic forms as done by Pseudomonas metafolia, which reduces toxic Cr, Hg, Pb, and Cd into nontoxic forms (Blake II et al. 1993); increase of metal bioavailability and enhance their uptake in metal ions such as Cr, Pb, Zn, As, and Ni by Diplachne fusca, Alyssum murale, and Pteris vittata which correlated with activities of various rhizobacteria (Al Agely et al. 2005;Gonzaga et al. 2006); as well as prevent translocation into plant by stabilizing metals in the rhizosphere (Praveen et al. 2019). ...
The contamination of agricultural soils with heavy metals is resulted from anthropogenic and/or natural sources which lead to adversely affect the environment and in turn human health. Rhizoremediation is a bioremediation form that harnesses the plant-microbes interaction in the rhizosphere for pollutant remediation. The microbiologists and ecologists have exploited the symbiosis between plants and microbes in the rhizosphere to remediate heavy metal contamination and alleviate such stress. High levels of heavy metals could inhibit the symbiosis between legumes and rhizobia. Research efforts are turned to harness genetic engineering techniques for producing genetically manipulated rhizobia to stimulate the symbiotic relationship under such a harsh situation with cleaning the polluted environment along with improving soil fertility. Genetic engineering includes introducing new genes conferring high heavy metals tolerance into the wild rhizobia or make rhizobia act as PGPR by stimulate phytohormone and/or siderophores production for reducing heavy metals stress.
... strain EA106 has been reported to significantly increase Fe plaque formation, thereby attenuating As uptake by rice roots (Lakshmanan et al., 2015). In another study, a strain of Pseudomonas maltophilio is reported to transform the mobile and toxic form of chromium (Cr(VI)) to the nontoxic and immobile form (Cr(III)) and also minimized the mobility of other toxic ions, such as Hg 21 , Pb 21 and Cd 21 (Blake et al., 1993;Park, Keyhan, & Matin, 1999). ...
Microbes are widely used in the enhancement of plant growth, yield, and nutrient uptake over a long period of time. Apart from biological control, microbes are also known to play a key role in the functioning of plant growth by changing their physiology and metabolism. Recently, intervention of microbes in the improvement of nutrient uptake by plant has gained momentum in the research field. Heavy metal contamination from different sources, such as agricultural practices or burning of fossil fuels, affects the microbial population density and physicochemical parameters of soil leading to the formation of unfertile soil. Plant growth–promoting rhizobacteria (PGPR) are the rhizosphere bacteria, which can ameliorate plant growth by interacting mutually with it.
Rice (Oryza sativa L.) is the most important cereal of the world and is the major staple food for the peoples of Asia, Africa, and Latin America. Present rice production management strategies mainly focus on the enormous use of synthetic chemical fertilizers and pesticides for enhancing the per hectare yield of the crop. Persistent and injudicious use of these chemicals including heavy metals has a toxic effect on nontarget microorganisms of the soil and causes undesirable changes in the environment. The use of PGPR as a biological approach for the amelioration of heavy metals toxicity to crop management in place of synthetic chemicals is ecologically sustainable for the environment. Moreover, the biological approach has a great potential in supplying plant nutrition and biocontrol of phytopathogens which eventually will lead to sustainable rice production. Among the different beneficial microflora, the PGPR promotes plant growth, and thereby is capable of affecting the growth and yield of numerous plant species of agronomic and ecological significance including O. sativa L.
This chapter highlights the role of PGPR in the amelioration of heavy metals toxicity to rice and soil–nutrient dynamics.
... In field experiment conditions, it was observed that the pH in the rhizosphere soil of the Cu-accumulating plant species (Elsholtzia) was significantly lower than in the bulk soil when plants were grown in Cu and other metal-contaminated soil (Peng et al. 2005). Blake et al. (1993) reported the conversion of mobile and toxic Cr VI to nontoxic and immobile Cr III with the reduction of environmental mobility of other toxic ions (Hg, Pb, Cd), by Pseudomonas maltophilia. ...
Different industrial, mining, agricultural and domestic activities produce a huge amount of wastes as by-products, which contaminate soil, surface water, and groundwater and cause ecological problems. Natural and traditional techniques are not very much sufficient to manage such type of pollutants/contaminants. The most affected area of environment is soil that indirectly affects biological interaction between plants and microorganisms. There is a need of highly eco-friendly approach to remove and manage such pollutants. Phytoremediation is a technique which remediates the contaminated site with and by the environmental phenomenon. Plants are the main tool of remediation in this technique. Phytoremediation includes the plant-mediated remediation of pollutants, like metal, organic, and hazardous wastes by its subclasses phytodegradation, phytovolatilization, phytoextraction, etc. This chapter includes all the phytoremediation techniques used to treat different types of contaminant site. It is an environment-friendly green technique which focused on the combined use of more than one phytoremediation approach for the successful remediation of the polluted area under field conditions.
... Mackova M et al. reported that complete degradation pathways are introduced in plants which leads to enhanced degradation of highly recalcitrant compounds such as explosives, PCBs and PAHs [52] . Pseudomonas metafolia is a microbe that reduces toxic Cr, Hg, Pb, and Cd into nontoxic forms [53] . Rhizobacteria facilitates the accumulation of nickel in Alyssum murale [54] . ...
In the race of development, various indiscriminate anthropogenic activities result in the accumulation of heavy metals in the soil and get entered into our food chain. Heavy metals are well known for their toxicity and become a major threat for human because of their deleterious health effects, especially in children. Because of the persistence of heavy metals, researchers are getting interested in low cost, and environment-friendly plant based remediation technology known as phytoremediation. In Phytoremediation, plants and associated soil microbes are used to eliminate the toxicant contaminants from the soil and is a successful substitute for engineering methods. Phytoremediation of metal contamination involved phytoextraction, phytostabilization, phytovolatilization and rhizofiltration etc. The drawback of this method is that it is observed more successful and fast in lesser contaminated areas in comparison to high contamination. The metal hyper-accumulators and some wild plants are found able to remove contaminants 10-500 times higher compared to cultivated ones.
... strain of S. maltophilia could tolerate high levels (0.1-50 mmol/L) of various metals, including the most toxic metals, such as Cd and Hg. Also Blake et al. (1993) reported that S. maltophilia O2, a strain isolated from soil at a toxic waste site, was able to catalyze the bioremediation and precipitation of numerous high-level toxic cations. These reports, including our data, suggest that S. maltophilia may have evolved various mechanisms to detoxify heavy metals. ...
An important mechanism for microbial resistance to mercury is its reduction into elemental mercury (facilitated by the merA gene). Thirty-eight microbial isolates from a variety of wastewater sources in Egypt were collected. Approximately 14 of the 38 isolates exhibited not only a high degree of tolerance to mercury (up to 160 ppm) but also a high degree of resistance to other tested heavy metals (Cu, Co, Ni, and Zn). From these 14, the 10 most resistant isolates were selected for further study and were found to include 9 Gram-negative and 1 Gram-positive bacterial strains. Multi-antibiotic-resistance profiles were detected for 6 out of the 10 selected isolates. All the tested Gram-negative isolates (n = 9) harbored a plasmid-encoded merA gene. The mercury removal effectiveness for the 10 selected isolates ranged between 50% and 99.9%, among which Stenotrophomonas maltophilia ADW10 recorded the highest rate (99.9%; at an initial mercury concentration of 20 ppm). To the best of our knowledge, this is the first study to (i) demonstrate the presence of a multimetal-resistant S. maltophilia bacterium with a high mercury tolerance capacity that would make it a suitable candidate for future bioremediation efforts in heavy-metal-polluted areas in Egypt and (ii) report Pseudomonas otitidis as one of the mercury-resistant bacteria.
... Pseudomonas metafolia is a microbe that reduces toxic Cr 61 to nontoxic Cr 31 . In addition to Cr, it also reduces Hg, Pb, and Cd into nontoxic forms (Blake et al., 1993). The rhizobacteria facilitates the uptake of nickel (Ni) in Alyssum murale (Abou-Shanab et al., 2005). ...
... Furthermore, several microorganisms including both fungi and bacteria were reported of having the capability of transforming noxious metals to their lesser toxic conditions. For instance, Pseudomonas maltophilia strain (isolated from contaminated soil) was reported of catalyzing the conversion and precipitation of several noxious metal oxyanions and cations, while Aspergillus niger (the oxalic and acitric acid producer) was documented of transforming Zn 3 (PO 4 ) 2 , Co 3 (PO 4 ) 2 and ZnO, insoluble inorganic metal composites into their corresponding insoluble metal oxalates [13,62,63]. ...
Phytoremediation is considered as a cost-effective and environmentally friendly technique for decontaminating environments that have been contaminated with heavy metal ions. The technique describes the use of plants and their concomitant microbes to mitigate environmental contaminations. However, conventional remediation techniques like chemical, thermal and physical treatment methods are too costly, and may end of causing more contamination to the environment. Phytoremediation practice provides a major information on the utilization of plants and their materials in decontaminating polluted environments. Heavy metals and other organic contaminants are among the most precarious substances released into the environment which have an eminent level of toxicity and sturdiness of both aquatic and terrestrial organisms. The review aimed at providing a broad understanding of utilizing various plants and their materials in decontaminating polluted environments with heavy metals and other organic contaminants. It also provided the general methods used in treating the aforementioned contaminants in an environment. The review further discussed the classes of phytoremediation like phytoextraction, phytovolatilisation, phytostabilization, phytotransformation, phytodegradation and phytofiltration. The generalized advantages and disadvantages of phytoremediation were ultimately highlighted.
... Besides, they reported that this strain could 72 reduce high concentration of selenite and tellurite to elemental state (Pages et al, 73 2008). The studies of Blake et al. have also reported that S. maltophilia O2, isolated 74 from soil at a toxic waste site, could catalyze the transformation and precipitation of 75 numerous high level toxic cations and oxyanions (Blake et al, 1993). These results 76 indicated that S. maltophilia might had various mechanisms to detoxify heavy metals. ...
Stenotrophomonas maltophilia is highly resistant to heavy metals, but the genetic knowledge of metal resistance in S. maltophilia is poorly understood. In this study, the genome of S. maltophilia Pho isolated from the contaminated soil near a metalwork factory was sequenced using PacBio RS II. Its genome is composed of a single chromosome with a GC content of 66.4% and 4434 protein-encoding genes. Comparative analysis revealed high syntney between S. maltophilia Pho and the model strain, S. maltophilia K279a. Then, the type and number of mechanisms of heavy metal uptake were analyzed firstly. Results showed that 7 unspecific ion transporter genes and 13 specific ion transporter genes, most of which were involved in iron transport. But the sulfate permeases belonging to the family of SulT/CysP that can uptake chromate and the high affinity ZnuABC/SitABCD were absent. Secondly, the putative genes controlling metal efflux were analyzed. Results showed that this bacterium encoded 5 CDFs, 1 copper exporting ATPase and 4 RND systems, including 2 CzcABC efflux pumps. Moreover, the putative metal transformation genes including arsenate and mercury detoxification genes were also identified. This study may provide useful information on the metal resistance mechanisms of S. maltophilia .
... Microbiallymediated reduction of selenite Se (VI) and Selenite Se (IV) to elemental Selenium is mediated by Clostridium, Citrobacter, Flavobacterium and Pseudomonas. Reduction of TeO 3 2− (toxic) to Te°is an evident means of detoxification in bacteria by Pseudomonas maltophilia (Blake et al., 1993) and by fungus Schizosaccharomyces pombe, giving black or grey colonies (Smith, 1974). Fungal strains Fusarium sp. ...
Bioligands (BL) present in plant and microbes are primarily responsible for their use in metal decontamination. Both primary (proteins and amino acid) and secondary (proliferated) response in the form of BL is possible in plants and microbes toward metal bioremediation. Structure of these BL have specific requirement for preferential binding towards a particular metal in biomass. The aim of this review is to explore various templates from BL (as metal host) for the metal detoxification/decontamination and associated bioremediation. Mechanistic explanation for bioremediation may involve the various processes like: (i) electron transfer; (ii) translocation; and (iii) coordination number variation. HSAB (hard and soft acid and base) concept can act as guiding principle for many such processes. It is possible to investigate various structural homolog of BL (similar to secondary response in living stage) for the possible improvement in bioremediation process.
... The bioavailability of heavy metals in soils is a function of its solubility (Ernst 1996) with pH and organic matter content being the main controlling factors (Gray et al. 1998). For example, a strain of Pseudomonas maltophilia was shown to reduce the mobile and toxic Cr 6+ to nontoxic and immobile Cr 3+ , and also to minimize environmental mobility of other toxic ions such as Hg 2+ , Pb 2+ , and Cd 2+ (Blake et al. 1993;Park et al. 1999). Chaudri et al. (1992) found that Rhizobium populations were reduced at concentrations >7 mg/kg soil in their Cd treatments. ...
A diverse array of rhizosphere bacteria colonize the most plants grown in the field. Beneficial bacterial communities in the soil are chemoattracted towards the plant roots in response to various compounds present in the root exudates. These beneficial associations improve plant health and crop yield either by enhancing the availability of nutrients, by releasing plant growth stimulating hormones, suppressing the diseases caused by pathogens/pests or by improving resistance to environmental stress. Some of the beneficial rhizosphere bacteria supply biologically fixed nitrogen, solubilize bound phosphorus and also increase the availability of other plant nutrients such as iron, manganese, calcium and sulphur. Plant growth stimulating hormones cause elongation of plant root and shoot leading to improved crop yield. Certain rhizosphere bacteria prevent disease development by killing the pathogens through production of antibiotics, bacteriocins, siderophores, hydrolytic enzymes and other secondary metabolites. Some rhizobacteria are involved in detoxifying the organic toxicants either through stimulation of microbial biodegradation in the rhizosphere or by uptake of pollutants/toxicants by the plant. Recently, tremendous progress has been made in characterizing the process of rhizosphere colonization, identification and cloning of bacterial genes involved in nitrogen fixation, phosphorus solubilization, in production of plant growth promoting substances and in suppression of plant diseases. This review describes the different kind interactions of rhizosphere bacteria with their plant hosts by which microbes can act beneficially for their efficient utilization in crop production.
... Root exudates, on the other hand promotes growth and metabolism of microorganisms to enhance the biodegradation of contaminants. In this way, both plants and microorganisms work together to accelerate the degradation reaction (Blake et al. 1993;Bais et al. 2003).The high removal of Amaranth dye is also contributed by the longer pathway of the baffles in the ABCW reactor which exposed the dye contaminated wastewater to more microbes and biofilm. Besides that, the variations in ORP values in the ABCW reactor which confirms that the multiple aerobic and anaerobic zones influenced the activity of the microbes to decolorize and mineralize the Amaranth dye. ...
The objective of this study is to determine the reduction efficiency of COD as well as the removal of color and Amaranth dye metabolites by the Aerobic-anaerobic Baffled Constructed Wetland Reactor (ABCW). The ABCW reactor was planted with common reed (Phragmite australis) where the HRT was set to 1 day and was fed with synthetic wastewater with the addition of Amaranth dye. Supplementary aeration was supplied in designated compartments of the ABCW reactor to control the aerobic and anaerobic zones. After Amaranth dye addition the COD reduction efficiency dropped from 98% to 91% while the color removal efficiency was 100%. Degradation of azo bond in Amaranth dye is shown by the UV-Vis Spectrum analysis which demonstrates partial degradation of Amaranth dye metabolites. The performance of the baffled unit is due to the longer pathway as there is the up-flow and down-flow condition sequentially thus allowing more contact of the wastewater with the rhizomes and micro-aerobic zones.
... While this relationship benefits the plant when growing naturally on contaminated soil, it proves detrimental to phytoextraction efforts (Jefferies et al, 2003; Xu et al, 2014). The AMF reduce the mobility of toxic metals by reducing them to a non-transportable state (Blake et al. 1993). To counteract the shielding effect of the AMF, phytoremediation sites must be treated with a chemical agent, such as benomyl, to arrest the function of the fungi (Hovsepyan & Greipsson, 2004; Zheljazkov & Astatkie, 2011). ...
Soil lead (Pb) contamination represents a major environmental and public health risk. Conventional Pb remediation methods are typically expensive and risk further environmental damage. Phytoextraction has emerged as an alternative heavy metal remediation method with the potential for reducing both economic cost and negative environmental effects. For this study, North American native switchgrass (Panicum virgatum) was chosen due to its ability to achieve high biomass yields across a variety of climates and environmental conditions. The switchgrass plants in this study were treated with chemical chelates, fungal suppressants, and nitric oxide (NO) donors with the intent of optimizing Pb phytoextraction. Soils collected from sites located in urban Atlanta were chemically manipulated with the intent to increase Pb bioavailability and uptake into harvestable switchgrass tissues. Ethylenediamintetraacetic acid (EDTA) is regarded as a highly effective chelate, though its long soil persistence leads to potential concerns about Pb mobilization into groundwater. Citric acid has been proposed and found success as an alternative chelate that has a significantly shorter soil persistence time and lower risk of ground water contamination; though its abilities to chelate Pb in a phytoextraction context are still being studied. In addition to a comparison of chelating agents, two fungal suppressants were also compared for their abilities to suppress arbuscular mycorrhizal fungi (AMF). Benomyl is frequently used as a fungal suppressant in phytoextraction research, but another alternative, propiconazole may be a more effective fungal suppressant. Exogenous nitric oxide (NO) donor application was also studied to determine the effects on switchgrass biomass and Pb uptake. Three exogenous NO donors were evaluated in the primary study: S-Nitroso-N-acetylpenicillamine (SNAP), sodium nitroprusside (SNP), and S-nitrosoglutathione (GSNO). Each exogenous NO donor was tested at multiple concentrations in the initial study, though no significant difference was found between any donor and concentration. In the second study, SNP (0.5 μM) was selected for application, but no significant difference was found between plants in SNP treatments and non-SNP treatments. In the second study, chemical applications of EDTA, citric acid, benomyl, propiconazole, and SNP were tested in combinations of chelate, fungal suppressant and NO donor or non-donor applied treatments. While both chelates exhibited increased Pb accumulation over the Control plants, the EDTA treatments showed increased Pb accumulation in both root and shoot tissues over the citric acid treatments. Despite the differences in Pb accumulation, there was no significant difference between translocation factors between any treatments. Total Pb phytoextraction was highest in EDTA chelate treatments with application of benomyl (EB) and propiconazole (EP). Application of benomyl and propiconazole demonstrated the ability of both broad-spectrum fungicides to reduce AMF colonization, allowing greater Pb phytoextraction; however, roots treated with propiconazole exhibited significantly decreased AMF colonization in comparison to roots treated with benomyl. Additionally, benomyl application resulted in significantly increased colonization of pathogenic fungi over the Control plants, while propiconazole application significantly reduced pathogenic fungi colonization.
... This helps in leaching of these contaminants from soils. For example, a strain of Pseudomonas maltophilia was shown to alter the mobile and toxic Cr 6+ into nontoxic and immobile Cr 3+ , and also to minimize environmental mobility of other toxic ions such as Hg 2+ , Pb 2+ and Cd 2+ [42]. ...
Soil, air and water pollution have become a global problem due to unprocessed emission of toxic heavy metals into the environment. The uncontrolled increase in release of hazardous heavy metals such as arsenic into the soil and water is mainly due to the untreated industrial waste. The accumulation of heavy metals causes damage not only to soil and water flora but also have deleterious effects on human health. The conventional methods such as thermal treatment, excavation and land fill, electro-reclamation and acid leaching used for degradation were time and cost consuming with release of toxic products. In nature, there are microorganisms residing in soil, which are capable of degrading toxic metals through phytoremediation. In phytoremediation, rhizobacteria play an important role. Rhizobacteria not only prevent contaminated soil's fertility but also enhance the growth of plants by release of special plant growth hormones. Phytohormones secreted by plant growth-promoting rhizobacteria (PGPR) are major chemicals involved in metal uptake. This in situ and environment friendly method of bioremediation is cost effective and efficient. The advance techniques such as genetic engineering have been introduced to increase the spectrum and degrading capacity of rhizobacteria.
... Volume Two example, a strain of Pseudomonas maltophilia was shown to reduce the mobile and toxic Cr 6+ to nontoxic and immobile Cr 3+ , and also to minimize environmental mobility of other toxic ions such as Hg 2+ , Pb 2+ , and Cd 2+ (Blake et al., 1993;Park et al., 1999). In addition, it has been estimated that microbial reduction of Hg 2+ generates a significant fraction of global atmospheric Hg 0 emissions (Keating et al., 1997). ...
... First, the rapid transformation of bacteria can change the metal bioavailability in soil. For instance, a strain of Xanthomonas maltophyla bacterium can be exposed for catalyzing the reduction and precipitation of highly mobile Cr ions from significantly less movable environmentally less hazardous compounds (Blake et al., 1993). Induced transformation of toxic metal ions including Pb 2þ , Hg 2þ , Au 3þ , Te 4þ , and Ag þ can also be found in some strains (Lasat, 2002). ...
Plant growth and metabolisms are regulated by some heavy metals found in Earth's crust because they are active constituents of various enzymes. However, their increased concentration may lead to different toxic effects, inhibiting plant growth and development. There are some plants that are capable of surviving in the presence of heavy metals, apparently by adapting the mechanism that involved in common homeostasis as well as removal of metal ions. Plants have diverse mechanisms for metal detoxification, enabling them to tolerate heavy metal stress. The defense systems against heavy metal stress include mycorrhizae, cellular exudates, plasma membrane, heat shock proteins, phytochelatins (PCs), metallothioneins (MTs), organic acids, and amino acids. All the mechanism involved the tolerance of heavy metal concentration at cellular level to avoid the negative impacts. Extracellular plants include roles for mycorrhizae and extracellular exudates in the plasma membrane either by dropping by absorption of heavy metal or by inducing the efflux pumping of metal ions. On the other hand, intracellularly heat shock proteins, MTs, organic acids, amino acids, and PCs also play a vital role in tolerance of different heavy metals. Few metal transporters have been identified in the past few years that actively participate in tolerance of metal specificity. Enhanced application of molecular genetics has shown their eminent contribution in understanding the mechanism of heavy metal tolerance in plants.
... Xanthomonas maltophyla (Blake et al., 1993), Escherichia coli and Pseudomonas putida (Lasat, 2002a) catalyze reduction and precipitation of highly mobile and environmentally less hazardous compounds. ...
Phytoremediation is an emerging technology which uses plants and their associated rhizospheric microorganisms to remove pollutants from contaminated sites. This plant based technology has gained acceptance in the past ten years as a cheap, efficient and environment friendly technology especially for removing toxic metals. Plant based technologies for metal decontamination are extraction, volatilization, stabilization and rhizofiltration. Various soil and plant factors such as soil's physical and chemical properties, plant and microbial exudates, metal bioavailability, plant's ability to uptake, accumulate, translocate, sequester and detoxify metal amounts for phytoremediation efficiency. Use of transgenics to enhance phytoremediation potential seems promising. Despite several advantages, phytoremediation has not yet become a commercially available technology Progress in the field is hindered by lack of understanding of complex interactions in the rhizosphere and plant based mechanisms which allow metal translocation and accumulation in plants. The review concludes with suggestions for future phytoremediation research.
... It was concluded from this study that, the bacterial strains reduced the uptake and consequent translocation of these metals to shoots and also synthesized phytohormones and ACC deaminase, which together accounted for increased growth of the test plant. In other study, a strain of Pseudomonas maltophilio transformed the mobile and toxic form of chromium (Cr VI) to non-toxic and immobile form (Cr III) and also minimized the mobility of other toxic ions, such as Hg 2+ , Pb 2+ and Cd 2+ (Blake et al. 1993;Park et al. 1999). From these and other studies, it seems reasonable to believe that the plant growth promoting rhizobacteria could be developed as inoculants to increase plant biomass and thereby to stabilize, re-vegetate and re-mediate metal-polluted soils. ...
... In the future, such measurements can be performed in 3D and with a higher temporal resolution, supplying a wealth of information about these greatly important but still to be understood biofilms. Moreover, the application of SECRaM using bio-precipitated noble metal particles can be extended from Shewanella biofilms to AgNp and AuNp precipitation in bioremediation [108] and nanoparticle biosynthesis applications, including the removal of Ag(I) from mining environments [109] and photographic waste [110], precipitation of AuNp from Au(III) contaminated water by Pseudomonas aeruginosa biofilms [111], removal of various metal species from waste electronic scrap leachate by Desulfovibrio desulfuricans [112], and production of AgNp by Aspergillus flavus [113], Morganella sp. [89,114], Lactobacillus [96], various cyanobacteria [115] and Pseudomonas stutzeri [88]. ...
Shewanella oneidensis MR-1 is an electroactive bacterium, capable of reducing extracellular insoluble electron acceptors, making it important for both nutrient cycling in nature and microbial electrochemical technologies, such as microbial fuel cells and microbial electrosynthesis. When allowed to anaerobically colonize an Ag/AgCl solid interface, S. oneidensis has precipitated silver nanoparticles (AgNp), thus providing the means for a surface enhanced confocal Raman microscopy (SECRaM) investigation of its biofilm. The result is the in-situ chemical mapping of the biofilm as it developed over time, where the distribution of cytochromes, reduced and oxidized flavins, polysaccharides and phosphate in the undisturbed biofilm is monitored. Utilizing AgNp bio-produced by the bacteria colonizing the Ag/AgCl interface, we could perform SECRaM while avoiding the use of a patterned or roughened support or the introduction of noble metal salts and reducing agents. This new method will allow a spatially and temporally resolved chemical investigation not only of Shewanella biofilms at an insoluble electron acceptor, but also of other noble metal nanoparticle-precipitating bacteria in laboratory cultures or in complex microbial communities in their natural habitats.
... Various bacterial and fungal microorganisms can facilitate transformation of toxic metals to their less toxic states. Pseudomonas maltophilia strain, isolated from soil at a toxic waste site in Oak Ridge, Tennessee, was reported to catalyze the transformation and precipitation various toxic metal cations and oxyanions [75]. Citric and oxalic acid producing Aspergillus niger, was reported to transform insoluble inorganic metal compounds ZnO, Zn 3 (PO 4 ) 2 and Co 3 (PO 4 ) 2 .to ...
Soil pollution due to heavy metals derived from anthropogenic activities is a major global concern. Detrimental effects of heavy metals on the environment and human health are now well understood. A major challenge is removal and reduction of heavy metal contamination. Of all the remediation techniques available for metal-contaminated soil, phytoremediation is the most cost-effective, environmentally friendly, and practical approach. Phytoremediation includes the removal, relocation, or reduction of contaminants using plants that hyperaccumulate these contaminants. On the basis of the mode of action, phytoremediation is subdivided into subclasses such as phytostabilization, phytofiltration, phytovolatilization, and phytoextraction. In this review, we discuss the need for phytoremediation and its approaches with a special context to the heavy metals.
... To promote the uptake efficiency of heavy metals by plants, many investigations have focused on the close relationship between plants and plant-growth-promoting rhizobacteria (PGPR). Some rhizobacteria can reduce the toxicity of heavy metals, resulting in the stimulation of plant growth (Black et al. 1993; Burd et al. 2000; De-Souza et al. 1999). They can excrete organic acids to enhance the bioavailability of heavy metals (Shanab et al. 2003). ...
During the last decades, heavy metals have become a common contaminant worldwide. Root-colonizing bacteria that exert beneficial effects on plant development directly or indirectly, often called as plant-growth-promoting rhizobacteria (PGPR), play an important role in the remediation of heavy-metal-contaminated soils. The prospect of manipulating rhizosphere microbial populations by inoculating beneficial bacteria to increase plant growth has shown considerable promise in laboratory and greenhouse studies, but responses have been variable under the field trials. In addition to their role in metal decontamination/removal, PGPR have also been found to facilitate plant growth in conventional soils by various mechanisms. These mechanisms include the suppression of phytopathogens by producing siderophores, synthesizing antifungal antibiotics, secreting fungal cell-wall-lysing enzymes, or hydrogen cyanide in addition to the release of growth-promoting hormones, solubilization of insoluble phosphate, and providing other essential nutrients to plants. Here in this chapter, the role of PGPR in metal especially cadmium decontamination is highlighted.
... Pseudomonas possesses autotrophic and heterotrophic metabolic pathways (Dijkhuizen and Harder, 1979). It not only respires NO 3 À and ClO 3 À (Samuelsson, 1985;Xu et al., 2004), but also reduces a variety of metal and metalloid with high valence state, including Cr(VI), Se(IV), Pb(II), and Cd(II) by utilizing specific functional enzymes (Blake et al., 1993). Pseudomonas putida transformed Cr(VI) to Cr(III) using a soluble enzyme relying on NADH or NADPH (Park et al., 2000). ...
Antimony (Sb), a toxic metalloid, is soluble as antimonate (Sb(V)). While bio-reduction of Sb(V) is an effective Sb-removal approach, its bio-reduction has been coupled to oxidation of only organic electron donors. In this study, we demonstrate, for the first time, the feasibility of autotrophic microbial Sb(V) reduction using hydrogen gas (H2) as the electron donor without extra organic carbon source. SEM and EDS analysis confirmed the production of the mineral precipitate Sb2O3. When H2 was utilized as the electron donor, the consortium was able to fully reduce 650 μM of Sb(V) to Sb(III) in 10 days, a rate comparable to the culture using lactate as the electron donor. The H2-fed culture directed a much larger fraction of it donor electrons to Sb(V) reduction than did the lactate-fed culture. While 98% of the electrons from H2 were used to reduce Sb(V) by the H2-fed culture, only 12% of the electrons from lactate was used to reduce Sb(V) by the lactate-fed culture. The rest of the electrons from lactate went to acetate and propionate through fermentation, to methane through methanogenesis, and to biomass synthesis. High-throughput sequencing confirmed that the microbial community for the lactate-fed culture was much more diverse than that for the H2-fed culture, which was dominated by a short rod-shaped phylotype of Rhizobium (α-Protobacteria) that may have been active in Sb(V) reduction.
As a consequence of development and industrialization, the excessive use of toxic organic and inorganic chemicals as well as heavy metals, has caused an uncontrolled accumulation of chemical waste in soil, water and air. Today, it has become a global issue since all living things suffer as a result of direct or indirect exposure to these chemicals. Bioremediation is a sustainable and economical solution to this environmental problem, where microorganisms in the ecosystem are used to convert and/or degrade and/or remove pollutants. This chapter summarizes the role of plant growth-promoting rhizbacteria as biological control agents in the biosorption of soil contaminants, including heavy metals and organic compounds. The bioremediation approaches are explained and research findings are discussed to serve as a guide for those interested in this subject.
Chromium toxicity is a major environmental concern as it is the chief environmental pollutant released by paint, stainless steel, and mining industries. In nature, chromium exists in two stable valance states: Cr(VI) and Cr(III). Cr(VI) is highly toxic and soluble at neutral pH, whereas Cr(III) is insoluble at normal pH and is less toxic. Thus, it is essential to draw strategies for mitigation of Cr(VI), and microbial reduction of toxic Cr(VI) has been identified as a bioremediation technique not only to detoxify chromium but also to recover the non-toxic Cr(III) by physical means. Chromate reductase, the central enzyme involved in bioreduction of Cr(VI) to Cr(III) may be both intracellular as well as extracellular in nature. Most of the chromate reductase enzyme belongs to the oxidoreductase group such as nitroreductase, iron reductase, quinone reductase, hydrogenase, flavin reductase, as well as NAD(P)H-dependent reductase. Detailed analysis of the structure of the enzymes will help us in the suitable application of these enzymes in bioremediation of metal-contaminated wastes.
As a result of rapidly increasing population and the related anthropogenic activities, our natural resources are becoming severely contaminated with various inorganic and organic compounds. Among the several remediation techniques available for removal of pollutants, phytoremediation is considered to be the most efficient and environment friendly. Phytoremediation is a process where plants and associated microbes are utilized for removal of harmful chemicals from the polluted sites. The rhizospheric microbiome is comprised of several bacteria, endophytes and AMF that plays significant role in plant growth and development. The rhizospheric microbiota facilitates nutrient availability, releases growth-promoting phytohormones and provides protection against abiotic and biotic stresses to plants. The interaction of these soilborne microbes with plants helps in uptake, sequestration and detoxification of contaminants from polluted sites. This chapter aims at highlighting the role of plant-microbe interactions in the process of phytoremediation. A detailed understanding of the plant-microbe interaction in phytoremediation will help in developing more efficient methods for detoxification of the polluted sites leading to environmental cleanup.
Bioaccumulation of heavy metal in biological systems is an important cause of concern for environmental health and safety. Arsenic is one of the most hazardous metalloid, deserves special attention on account of its toxicity and carcinogenicity in the environment. The present paper reviews the current knowledge about the toxicity, carcinogenicity, and remediation strategies for arsenic removal from the environmental systems. The toxicity of arsenic depends mainly upon its speciation. Exposures of arsenic in drinking water lead to the cancer of skin, lungs, and bladder. The paper gives an insight into the arsenic removal by physicochemical processes, and the feasibility of using biological methods, the use of bacteria, and algae, its potential for sustainable use and environmental compatibility. The ability of the microbes to remove the metalloid via the process of mobilization and sorption of arsenic through the oxidation, reduction, methylation, and co-precipitation has been discussed in this paper. Lastly, the use of in silico approach to study the remediation of arsenic with the aid of systemic strategies, genomics, and molecular docking.
A glutathione reductase (GSHR)-like enzyme in Pseudomonas moraviensis stanleyae was previously implicated as underlying the bacterium's remarkable SeO3²⁻ tolerance. Herein, this enzyme is sequenced, recombinantly expressed, and fully characterized. The enzyme is highly adapted for selenodiglutathione substrates (Km = 336 μM) compared to oxidized glutathione (Km = 8.22 mM). The recombinant expression of this enzyme in the laboratory strains of Escherichia coli conveys a 10-fold increase in IC90 for SeO3²⁻. Moreover, selenium nanoparticles are observed when the enzyme is overexpressed in the cells exposed to SeO3²⁻, but not in the corresponding no-enzyme controls. The analyses of the structural homology models of the enzyme reveal changes in the parts of the enzyme associated with product release, which may underlie the Se substrate specialization. Combined, the observations of adaptation to Se reduction over oxidized glutathione reduction as well as the portability of this nanoparticle-mediated SeO3²⁻ tolerance into other cell lines suggest that the P. moraviensis GSHR may be better described as a GSHR-like metalloid reductase.
Phytoextraction is a green technique for the removal of soil contaminants by plants uptake with the subsequent elimination of the generated biomass. The halophytic plant Suaeda vera Forssk. ex J.F.Gmel. is an native Mediterranean species able to tolerate and accumulate salts and heavy metals in their tissues. The objective of this study was to explore the potential use of S. vera for soil metal phytoextraction and to assess the impact of different chelating agents such as natural organic acids (oxalic acid [OA], citric acid [CA]), amino acids (AA) and Pseudomonas fluorescens bacteria (PFB) on the metal uptake and translocation. After 12 months, the highest accumulation of Cu was observed in the root/stem of PFB plots (17.62/8.19 mg/kg), in the root/stem of CA plots for Zn (31.16/23.52 mg/kg) and in the root of OA plots for Cr (10.53 mg/kg). The highest accumulation of metals occurred in the roots (27.33–50.76 mg/kg). Zn was the metal that accumulated at the highest rates in most cases. The phytoextraction percentages were higher for Cu and Zn (∼2%) with respect to Cr (∼1%). The percentages of metal removal from soil indicate the need to monitor soil properties, to recognize the influence of each treatment and to increase the concentration of bioavailable metals by the use of agricultural management practices aimed at promoting plant growth.
In the present work we have identified a glutathione reductase like metalloid reductase (GRLMR) responsible for mediating selenite tolerance in Pseudomonas moravenis stanleyae through the enzymatic generation of Se(0) nanoparticles. This enzyme has an unprecedented substrate specificity for selenodiglutathione (K<sub>m</sub>= 336 μM) over oxidized glutathione (K<sub>m</sub>=8.22 mM). This enzyme was able to induce selenite tolerance in foreign bacterial cell lines by increasing the IC<sub>90</sub> for selenite from 1.9 mM in cell lacking the GRLMR gene to 21.3 mM for cells containing the GRLMR gene. It was later confirmed by STEM and EDS that Se nanoparticles were absent in control cells and present in cells expressing GRLMR. Structural analysis suggests the lack of a sulfur residue in the substrate/product binding pocket may be responsible for this unique substrate specificity.
Abstract This study aims to enrich Sb(V)-reducing bacterial communities from Sb-contaminated soils using various electron donors for bioremediation of Sb-contaminated sites and recovery of Sb from wastewater. When the organic electron donors were used, Sb(V) reduction rates were 2–24 times faster but electron recoveries were 24–59% lower compared to the culture using inorganic electron donor. The morphological crystallizations of the antimony-reduced precipitates were completely different depending on the electron donor. Different microbial populations were enriched with various electron donors but most commonly, only Proteobacteria and Firmicutes phyla were enriched from a diversified soil microbial community. Geobacter sp. seemed to be an important bacterium in organic electron donors-fed cultures whereas an unclassified Rhodocyclaceae was dominant in inorganic electron donor-fed cultures. The results indicated that organic electron donors especially sugar groups were preferable options to obtain rapid Sb(V)-reduction whereas inorganic electron donor like H2 was better option to achieve high electron recovery.
The priority pollutant antimony (Sb) exists primarily as Sb(V) and Sb(III) in natural waters, and Sb(III) is generally with greater mobility and toxicity than Sb(V). The bio-reduction of Sb(V) would not become a meaningful Sb-removal process unless the accumulation of produced dissolved Sb(III) could be controlled. Here, we examined the dissimilatory antimonate bio-reduction with or without the coexistence of sulfate using Sb-acclimated biomass. Results demonstrated that 0.8 mM Sb(V) was almost completely bio-reduced within 20 h along with 48.6% Sb(III) recovery. Kinetic parameters qmax and Ks calculated were 0.54 mg-Sb mg-DW⁻¹ h⁻¹ and 41.96 mg L⁻¹, respectively. When the concentrations of coexisting sulfate were 0.8 mM, 1.6 mM, and 4 mM, the reduction of 0.8 mM Sb(V) was accomplished within 17, 9, and 5 h, respectively, along with no final Sb(III) recovery. Also, the bio-reduction of sulfate occurred synchronously. The precipitated Sb2O3 and Sb2S3 were characterized by scanning electron microscopy coupled with energy dispersive spectrometer, X-ray diffraction, and X-ray photoelectron spectroscopy. Compared with bacterial compositions of the seed sludge obtained from anaerobic digestion tank in a wastewater treatment plant, new genera of Pseudomonas and Geobacter emerged with large proportions in both Sb-fed and Sb-sulfate-fed sludge, and a small portion of sulfate reduction bacteria emerged only in Sb-sulfate-fed culture.
Environmental contamination by toxic metals is of considerable economic and environmental significance [1–5] although the influence of microbiological processes on such contamination and their potential for bioremediation are dependent on the organisms involved and on physical and chemical factors. Several microbial mechanisms can solubilize metals, increasing their bioavailability and potential toxicity, whereas others immobilize them and reduce bioavailability. The relative balance of mobilization and immobilization processes varies depending on the organism (s), their environment and physicochemical conditions. As well as being a natural component of biogeochemical cycles for metals and associated elements, these processes may be exploited for the treatment of contaminated solid and liquid wastes [2, 4, 6–8].
This study was conducted to determine the microbe-chromate [Cr(VI)] interaction and the effect of quinoid analogue anthraquinone-2-sulfonate (AQS) on aerobic Cr(VI) reduction by Intrasporangium chromatireducens Q5-1. The addition of redox mediator AQS, which might expedite the electron transfer, promoted Cr(VI) bioreduction. Addition of carbon sources, such as maltose, acetate, sucrose and lactose stimulated the AQS-promoted Cr(VI) reduction of strain Q5-1. Induction experiment clarified that the enzyme involves in the Cr(VI) reduction is constitutive. Energy-dispersive spectroscopy (EDS) spectra showed the existence of trace Cr distributed on the cell surface. X-ray photoelectron spectroscopy (XPS) analysis revealed that the Cr(III) complex was bound to the cell surface (0.87%, atomic percent). The spectra shifts detected by Fourier transform infrared (FTIR) spectroscopy indicated that Cr(III) was bound to the carbonyl and amide groups. In addition, Cr(VI) reduction by different cell fractions showed that Cr(VI) reduction was occurred extracellularly rather than intracellularly. The results disclosed that Cr(VI) detoxification of strain Q5-1 was mainly associated with extracellular Cr(VI) reduction process in combination with trace Cr(III) adsorption on the cell surface. A schematic figure depicting the interactions between strain Q5-1 and Cr(VI) was presented. This study enhanced the understanding of the microbe-Cr(VI) interaction mechanism and revealed the AQS-promoted aerobic Cr(VI) reduction of strain Q5-1. Such strain and quinoid analogue-mediated bacterial Cr(VI) reduction may facilitate the bioremediation for Cr(VI)-polluted environment.
The supply of minerals in plants is provided by the absorption of compounds dissolved in soil. Plants are also exposed to dissolved toxic heavy metals. Since plants cannot avoid contacts with heavy metals they developed a number of mechanisms decreasing the toxic effects. The important factors are, e.g. root exudates, soil microorganisms, plasmatic membrane, membrane transporters, heat-shock proteins, phytochelators, metallothioneins, organic acids and amino acids are introduced.
Pollution of the biosphere by the toxic metals is a global threat that has accelerated dramatically since the beginning of industrial revolution. The primary source of this pollution includes the industrial operations such as mining, smelting, metal forging, combustion of fossil fuels and sewage sludge application in agronomic practices. The metals released from these sources accumulate in soil and in turn, adversely affect the microbial population density and physico-chemical properties of soils, leading to the loss of soil fertility and yield of crops. The heavy metals in general cannot be biologically degraded to more or less toxic products and hence, persist in the environment. Conventional methods used for metal detoxification produce large quantities of toxic products and are cost-effective. The advent of bioremediation technology has provided an alternative to conventional methods for remediating the metal-poisoned soils. In metal-contaminated soils, the natural role of metal-tolerant plant growth promoting rhizobacteria in maintaining soil fertility is more important than in conventional agriculture, where greater use of agrochemicals minimize their significance. Besides their role in metal detoxification/removal, rhizobacteria also promote the growth of plants by other mechanisms such as production of growth promoting substances and siderophores. Phytoremediation is another emerging low-cost in situ technology employed to remove pollutants from the contaminated soils. The efficiency of phytoremediation can be enhanced by the judicious and careful application of appropriate heavy-metal tolerant, plant growth promoting rhizobacteria including symbiotic nitrogen-fixing organisms. This review presents the results of studies on the recent developments in the utilization of plant growth promoting rhizobacteria for direct application in soils contaminated with heavy metals under a wide range of agro-ecological conditions with a view to restore contaminated soils and consequently, promote crop productivity in metal-polluted soils across the globe and their significance in phytoremediation.
Legumes are considered the appropriate crops for raising the productivity and recovery of marginal lands through symbiosis with nodule-forming bacteria collectively called rhizobia. Cultivated fields around the world including India are often irrigated by metal-contaminated groundwater and surface water. This practice poses a significant risk to both agroecosystems and human health via food chain. Therefore, metal removal from contaminated soils is urgently required. In this context, conventional technologies for metal removal have been employed, but they are expensive and disruptive. The use of biological materials including both plants (phytoremediation) and microbial communities in the remediation of polluted environments, on the contrary, has been found environment friendly and inexpensive. Leguminous plants have been found important in this regard due to their bioremediation potential and ability to provide essential nutrient nitrogen to plants in nitrogen deficient soils through symbiosis with rhizobia. The role of Rhizobium-legume symbiotic association in alleviating metal toxicity is reviewed and highlighted.
Heavy metals are more widespread around the world and dangerous for biosphere because they cannot be degraded or destroyed rather tend to be bioaccumulated. Plants can survive even in the extreme environmental conditions, but some environmental factors can affect its various growth aspects and hence the plant productivity. The problem of heavy metal toxicity is further aggravated by the persistence of the metals in the environment. Toxic heavy metals entering the plant tissues inhibit most physiological processes at all levels of metabolism. The extent of inhibition of photosynthesis, ion water uptake, and nitrate assimilation is greatly dependent on the concentration of the metal ions, sensitivity, and tolerance of the plant. There is, therefore, a pressing need to deal with the problem of excess metal already present in the soil and to prevent future contamination.
Our atmosphere, water resources and soil are becoming increasingly contaminated with inorganic and organic compounds as a result of anthropogenic-driven inputs, mainly from industry, mining, motorized traffic, agriculture, logging and military actions. Alleviation and prevention of environmental pollution can be achieved by utilization of plants and their associated microbes. Recent advances in plant–microbe interaction research revealed that plants are able to shape their rhizosphere microbiome through active secretion of substrates that are known to vary between plant species. Soil-borne microorganisms such as actinobacteria, algae, protozoa and different types of bacteria having different capabilities of functional activities can vary extensively in soils and occur in associations in the rhizosphere of plants. Microbial associations are known to affect mobility and availability of substances to the plant through the release of chelating agents, acidification, phosphate solubilization and redox changes and exudates derived from the plant can help to stimulate the survival and action of these microorganisms. A broad knowledge about the mechanisms in plants for the uptake, translocation, storage, and detoxification of contaminants, and interactions between plants and microorganisms are critical in developing technologies and best management practices for environmental clean-up. A comprehensive understanding of interactions between plants and rhizospheric microorganisms in the rhizosphere and plant-based processes will provide new opportunities to develop more efficient plants and better management practices for removal of contaminants. This chapter reviews plant–microbe interactions in phytoremediation with particular reference to the microbial dynamics in the rhizosphere of plants growing on contaminated soils.
Sediment samples contaminated with metals arising from mine tailings drainage were obtained from Lower Moose Lake in the Onaping region near Sudbury, Ontario, Canada. The samples were examined by electron microscopy, selected-area electron diffraction and energy-dispersive X-ray spectroscopy. Individual bacterial cells and their remains were prominent as nucleation sites for both metal sulfides and a complex polymorphic (Fe,Al)-silicate. The principal metal sulfide species associated with the bacteria were amorphous mackinawite (FeS1 - x) and microcrystalline millerite (NiS). Trace amounts of Cu and Zu were also detected in some of the sulfide precipitates. At least two structural forms of the (Fe,Al)-silicate were present, and energy-dispersive X-ray spectroscopy point analyses revealed corresponding differences in chemical composition. Poorly ordered limonitic clay-type phases had a granular morphology and contained less Fe than well-developed crystalline material which generated hexagonal diffraction patterns with reflections (d = 4.60 and 2.55 Ȧ) characteristic of an interstratified chamositic clay.
Buthionine sulfoximine (S-n-butyl homocysteine sulfoximine), the most potent of a series of analogs of methionine sulfoximine thus far studied (Griffith, O.W., Anderson, M.E., and Meister, A. (1979) J. Biol. Chem. 254, 1205-1210), inhibited gamma-glutamylcysteine synthetase about 20 times more effectively than did prothionine sulfoximine and at least 100 times more effectively than methionine sulfoximine. The findings support the conclusion that the S-alkyl moiety of the sulfoximine binds at the enzyme site that normally binds the acceptor amino acid. Thus, the affinity of the enzyme for the S-ethyl, S-n-propyl, and S-n-butyl sulfoximines increases in a manner which is parallel to those of the corresponding isosteric acceptor amino acid substrates, i.e. glycine, alanine, and alpha-aminobutyrate. Buthionine sulfoximine did not inhibit glutamine synthetase detectably, nor did it produce convulsions when injected into mice. Injection of buthionine sulfoximine into mice decreased the level of glutathione in the kidney to a greater extent (less than 20% of the control level) than found previously after giving prothionine sulfoximine. alpha-Methyl buthionine sulfoximine was also prepared and found to be almost as effective as buthionine sulfoximine; this compound would not be expected to undergo substantial degradative metabolism. Buthionine sulfoximine and alpha-methyl buthionine sulfoximine may be useful agents for inhibition of glutathione synthesis in various experimental systems.
Washed cells of Enterobacter cloacae HO1 reduced hexavalent chromium (chromate: CrO4(2-) anaerobically. Chromate reductase activity was preferentially associated with the membrane fraction of the cells. Right-side-out membrane vesicles prepared from E. cloacae cells showed high chromate reductase activities when ascorbate-reduced phenazine methosulfate was added as an electron donor.
Reduction of hexavalent chromium (chromate) to less-toxic trivalent chromium was studied by using cell suspensions and cell-free supernatant fluids from Pseudomonas putida PRS2000. Chromate reductase activity was associated with soluble protein and not with the membrane fraction. The crude enzyme activity was heat labile and showed a Km of 40 microM CrO4(2-). Neither sulfate nor nitrate affected chromate reduction either in vitro or with intact cells.
Four bacteria, Bacillus cereus, B. subtilis, Escherichia coli, and Pseudomonas aeruginosa, were examined for the ability to remove Ag+, Cd2+, Cu2+, and La3+ from solution by batch equilibration methods. Cd and Cu sorption over the concentration range 0.001 to 1 mM was described by Freundlich isotherms. At 1 mM concentrations of both Cd2+ and Cu2+, P. aeruginosa and B. cereus were the most and least efficient at metal removal, respectively. Freundlich K constants indicated that E. coli was most efficient at Cd2+ removal and B. subtilis removed the most Cu2+. Removal of Ag+ from solution by bacteria was very efficient; an average of 89% of the total Ag+ was removed from the 1 mM solution, while only 12, 29, and 27% of the total Cd2+, Cu2+, and La3+, respectively, were sorbed from 1 mM solutions. Electron microscopy indicated that La3+ accumulated at the cell surface as needlelike, crystalline precipitates. Silver precipitated as discrete colloidal aggregates at the cell surface and occasionally in the cytoplasm. Neither Cd2+ nor Cu2+ provided enough electron scattering to identify the location of sorption. The affinity series for bacterial removal of these metals decreased in the order Ag greater than La greater than Cu greater than Cd. The results indicate that bacterial cells are capable of binding large quantities of different metals. Adsorption equations may be useful for describing bacterium-metal interactions with metals such as Cd and Cu; however, this approach may not be adequate when precipitation of metals occurs.
The ability to reduce Hg(II) to Hg(0), which is determined by a plasmid-borne gene in Escherichia coli, is conferred by a Hg(II)-inducible activity which is located in the cytoplasm rather than in the periplasmic space of the cell. This Hg(II)-reducing activity can be isolated from the supernatant of a 160,000 x g centrifugation after French Press disruption of the cells. The activity is dependent on glucose-6-phosphate, glucose-6-phosphate dehydrogenase, and 2-mercaptoethanol, but is not enhanced by added nicotinamide adenine dinucleotide phosphate. Treatment of the active fraction with N-ethylmaleimide causes irreversible loss of the Hg(II)-reducing activity. Unlike the Hg(II)-reducing activity found in intact cells, the cell-free activity is not inhibited by toluene, potassium cyanide, or m-chlorocarbonylcyanide-phenylhydrazone; however, it is inhibited by Ag(I) and phenylmercuric acetate to the same extent as the activity in intact cells. Neither phenylmercuric acetate nor methylmercuric chloride is reduced to Hg(0) by the cell-free activity. Au(III), however, is a substrate for the cell-free activity; it is reduced to metallic colloidal Au(0).
The flavoprotein mercuric reductase catalyzes the two-electron reduction of mercuric ions to elemental mercury using NADPH as an electron donor. It has now been purified from Pseudomonas aeruginosa PAO9501 carrying the plasmid pVS1. In this plasmid system, where the mer operon is on the transposon Tn501, mercuric reductase comprises up to 6% of the soluble cellular protein upon induction with mercurials. The purification is a rapid (two-step), high yield (80%) procedure. Anaerobic titrations of mercuric reductase with dithionite revealed the formation of a charge transfer complex with an absorbance maximum around 540 nm. Striking spectroscopic similarities to lipoamide dehydrogenase and glutathione reductase were observed. These two enzymes, which catalyze the transfer of electrons between pyridine nucleotides and disulfides, are flavoproteins which contain an oxidation-reduction-active cysteine residue at the active site. The expectation that mercuric reductase contains a similar electron acceptor was confirmed when it was shown that mercuric reductase has the capacity to accept four electrons per FAD-containing subunit, and that two thiols become kinetically titrable by 5,5'-dithiobis-(2-nitrobenzoate) upon reduction with NADPH. These are characteristic features of the disulfide reductase class of flavoproteins. Further similarities with at least one of these enzymes, lipoamide dehydrogenase, include the E/EH2 midpoint potential (-269 mV), fluorescence properties, and extinction coefficients of E and EH2. Preliminary observations relevant to an understanding of the mechanism of mercuric reductase are discussed.
In batch cultures of Zoogloea ramigera the maximum rate of exopolysaccharide synthesis occurred in a partly growth-linked process. The exopolysaccharide was attached to the cells as a capsule. The capsules were released from the cell walls after 150 h of cultivation, which caused the fermentation broth to be highly viscous. Ultrasonication could be used to release capsular polysaccharide from the microbial cell walls. Treatment performed after 48 to 66 h of cultivation revealed exopolysaccharide concentration and apparent viscosity values in accordance with values of untreated samples withdrawn after 161 h of cultivation. The yield coefficient of exopolysaccharide on the basis of consumed glucose was in the range of 55 to 60% for batch cultivations with an initial glucose concentration of 25 g liter. An exopolysaccharide concentration of up to 38 g liter could be attained if glucose, nitrogen, and growth factors were fed into the batch culture. The oxygen consumption rate in batch fermentations reached 25 mmol of O(2) liter h during the exopolysaccharide synthesis phase and then decreased to values below 5 mmol of O(2) liter h during the release phase. The fermentation broth showed pseudoplastic flow behavior, and the polysaccharide was not degraded when growth had ceased.
When hexavalent chromium (Cr⁶⁺) tolerant Pseudomonas ambigua G-l was cultivated in nutrient broth containing 150 ppm Cr⁶⁺, the Cr⁶⁺ content of the broth rapidly decreased. The Cr⁶⁺ reducing enzyme found in a cell-free extract of P. ambigua G-l required NADH but not NADPH as a hydrogen donor for the reduction of Cr⁶⁺. The specific activities of cell-free extracts of several Cr⁶⁺ sensitive mutants derived from P. ambigua G-l showed decreases to one fourth to one tenth of that of P. ambigua G-l. Glucose protected the Cr⁶⁺ reducing enzyme against inactivation on dialysis. © 1987, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.
When hexavalent chromium (Cr6+) tolerant Pseudomonas ambigua G-l was cultivated in nutrient broth containing 150 ppm Cr6 +, the Cr6+ content of the broth rapidly decreased. The Cr6+ reducing enzyme found in a cell-free extract of P. ambigua G-l required NADH but not NADPH as a hydrogen donor for the reduction of Cr6 +. The specific activities of cell-free extracts of several Cr6+ sensitive mutants derived from P. ambigua G-l showed decreases to one fourth to one tenth of that of P. ambigua G-l. Glucose protected the Cr6+ reducing enzyme against inac-tivation on dialysis.
This article reviews the principal factors affecting the feasibility of recovering nonferrous metals from industrial wastes. Major emphasis is on available separation process technologies with potential for metal recovery and the economics of recycling. Consideration is also given to government regulations and the strategic character of certain metals that provide important incentives for recycling.
Manganese‐reducing bacteria were isolated from a manganiferous silver ore mining site using enrichment procedures. The most rapid Mn(IV) reducer was identified as Bacillus polymyxa and was designated as strain D1. Isolate D1 has no growth‐factor requirements and is mesophilic and neutrophilic. D1 respires glucose aerobically, under which conditions cyanide is bactericidal. Nonfermentable substrates such as lactate, acetate, citrate, and succinate cannot serve as sole carbon sources. D1 ferments glucose anaerobically, producing acetic acid, ethanol, and butanediol as major metabolic end products. Both anaerobic conditions and direct physical contact with pyrolusite (MnO2) particles were necessary for manganese reduction. Strain D1 is unique in that manganese serves as an ancillary electron acceptor during anaerobic fermentation. Kinetic experiments showed that D1 reduced manganese three to five times as rapidly as the widely studied Mn(IV)/Fe(III)‐reducing microorganisms Shewanella putrefaciens MR‐1 and Shewanella putrefa‐ciens sp. 200. Strain D1 is capable of liberating silver via the reductive dissolution of refractory manganiferous ores.
Arsenazo III forums blue 1:1 complexes with zinc (II) and cadmium (II) in alkaline media, the absorpion maxima occurring at 590 nm and 600 nm, respectively; the molar absorptivities are 28,000 and 26,000, respectively. Halide ions and allyl alcohol increase the sensitivity of the zinc (II) –arsenazo III reaction. With iodide and allyl alcohol, molar absorptivities increase to 42,800 and 38,500 respectively, owing to the formation of ternary complexes. Zinc(II) and cadmium(II) can be determined in the presence of each other if suitable masking agents are used: 21 μg of zinc can be determined in the presence of 110 mg of cadmium with 10% ammonium fluoride, and 35.6 μg of cadmium in the presence of 120 μg of zinc with pyridine nitrate. The conditional stability constants of the zinc(II)- and cadmium(II) - arsenazo III complexes are given.
The orange-red complex formed between zirconium(IV) and 4-(2-pyridylazo)-resorcinol (1∶1) at pH 2.5, in presence of ascorbic acid and phthalate buffer, is used for spectrophotometric determination of zirconium, the absorbance being measured at 540 nm. Beer's law is obeyed for zirconium concentration of 0.5,μg to 5.0μg per ml. Molar absorptivity is 6.75×103. Apparent formation constant (log K) of the complex is 5.664±0.2. The method has sensitivity of 0.013μg of zirconium per cm2 and relative standard deviation ±1.30%.
This book presents the scientific basis for using microbial biomass to remove metals from solution. Reports on current and potential microbial technology, including bioleaching of ores, bio-benefication of ores and fossil fuels, metal recovery from solution, and microbial EOR. Examines how microorganisms used in these technologies might improve through genetic engineering.
The origin of hydrogen sulfide in southeastern Montana groundwaters was investigated. Sulfate‐reducing bacteria were detected in 25 of 26 groundwater samples in numbers ranging from 2.0 × 10 to greater than 2.4 × 10 bacteria per 100 ml. Stable sulfur isotope fractionation studies indicated a biological role in sulfate reduction. However, sulfate‐reducing activity as determined by use of a radioactive sulfur isotope was observed in only 1 of 16 samples. It is postulated that bacterial dissimilatory sulfate reduction is responsible for a major portion of the sulfide produced in these groundwaters and that these bacteria are most likely active in the adsorbed state, possibly in subsurface microzones where environmental conditions are conducive to sulfate reduction.
The biogeochemistry of Zn, Cd, Cu, Hg, and Fe in lakes and streams polluted by mine and smelter wastes emitted at Flin Flon, Canada, was investigated. In Schist Lake, a repository for both tailings-pond drainage and sewage, green algal blooms generated by nutrients from sewage promote entrapment of metals in sediments by (1) accumulation of metals from solution by algal seston, with preferential uptake of Zn, the most abundant metal, followed by sinking of the seston; and (2) production of H2S during decomposition of dead algae, resulting in sulfide precipitation. Metals are partially resolubilized from seston as it decomposes while sinking. Preferential retention of Cu by sinking seston and by mud promotes Cu enrichment in the mud but the Cu/Zn ratio of mud varies with the Cu/Zn ratio of surface water seston. In bottom muds, partitioning of a metal between sulfide and organic matter is strongly dependent on the stability of the metal sulfide as measured by its standard entropy, the proportion of sulfide-bound metal decreasing in the order Hg>Cd>Cu>Fe>Zn. When sulfide-rich muds were heated under helium, x-ray diffraction revealed abundant well-crystallized ZnS (sphalerite) containing Cd, Hg, and Fe; only poorly crystallized traces of the mineral were detected in unheated mud, however. Cu sulfide failed to crystallize, suggesting interference by sorbed impurities. Metals were concentrated in H2S-rich muds and extraction of muds with various solvents and by electrodialysis showed that sulfide was much more effective than organic matter in suppressing remobilization of metals. Remobilized Cu is probably bound to organic complexing agents. Some extractable complexing agents bind Cu preferentially with respect to Zn and Cd but others preferentially bind Zn and Cd; the complexes, being stable in the presence of free sulfide, may cause some release of metals from sulfide-rich muds in nature.
These results indicate that introduction of sewage together with heavy-metal effluents into settling ponds could be an effective and economic method for limiting heavy-metal pollution of natural waters.
Pseudomonas fluorescens LB300 is a chromateresistant strain isolated from chromium-contaminated river sediment. Chromate resistance is conferred by the plasmid pLHB1. Strain LB300 grew in minimal salts medium with as much as 1000 g of K2CrO4 ml–1, and actively reduced chromate to Cr(III) while growing aerobically on a variety of substrates. Chromate was also reduced during anaerobic growth on acetate, the chromate serving as terminal electron acceptor. P. fluorescens LB303, a plasmidless, chromatesensitive variant of P. fluorescens LB300, did not grow in minimal salts medium with more than 10 g of K2CrO4 ml–1. However, resting cells of strain LB303 grown without chromate reduced chromate as well as strain LB300 cells grown under the same conditions. Furthermore, resting cells of chromate-sensitive Pseudomonas putida strain AC10, also catalyzed chromate reduction. Evidently chromate resistance and chromate reduction in these organisms are unrelated. Comparison of the rates of chromate reduction by chromate grown cells and cells grown without chromate indicated that the chromate reductase activity is constitutive. Studies with cell-free extracts show that the reductase is membrane-associated and can mediate the transfer of electrons from NADH to chromate.
The soluble form of silver is the most inhibitory to bacteria. However, this toxicity can be reduced by complexation with phosphates, sulphides and chloride. Silver resistant bacteria have been described in the scientific literature. Certain bacterial species, such as Thiobacillus ferrooxidans and T. thiooxidans, can bioaccumulate silver during the leaching of sulphide ore minerals. It is also known that silver resistance is plasmid encoded in certain bacterial isolates. However, the exact mechanism of resistance is not known as very little information is available on silver uptake, possible silver efflux mechanisms or binding to specific cellular components. The paucity of knowledge on silver resistance and accumulation indicates that this area of research deserves further study.
Aspergillus niger, Penicillium spinulosum, Verticillium psalliotae and Porta placenta cause the formation of copper oxalate crystals when grown in a copper containing medium. Results are discussed in relation to the copper tolerance mechanisms of those fungi.
PAN(1-(2-pyridylazo)-2-naphthol) is proposed for the solvent extraction and spectrophotometric determination of manganese, iron, cadmium, mercury, gallium, and yttrium. The reagent, which is highly specific for iron, has been applied to the determination of iron in clay and anorthosite. The separation of yttrium from lanthanum and the separation of manganese from nickel were successful.RésuméLe 1-(2-pyridylazo)-2-naphtol est proposé pour l'extraction dans solvant et le dosage spectrophotométrique du manganèse, du fer, du cadmium, du mercure, du gallium et de l'yttrium. Les séparations yttrium-lanthane et manganèse-nickel sont décrites.ZusammenfassungFür die Extraktion durch Lösungsmittel und zur spektrophotometrischen Bestimmung von Mn, Fe, Cd, Hg, Ga und Y wird PAN (1-(2-Pyridylazo)-2-naphthol) als Reagenz vorgeschlagen. Es werden die Trennungen des Yttriums von Lanthan und des Mangans von Nickel beschrieben.
Aspergillus niger oxidized the sulphides of copper, lead and zinc, but not cadmium, to sulphate. With the exception of cadmium sulphide, the sulphide particles in the medium were adsorbed on to the surface of the mycelium, a process which is apparently associated with sulphide oxidation. Traces of thiosulphate and tetrathionate were also produced, and the medium was acidified. Smaller amounts of sulphate were found in sulphide-amended media in which Trichoderma harzianum grew compared with media supporting A. niger, although thiosulphate and tetrathionate were produced more consistently. As the amounts of sulphate taken up by the two fungi could not be accurately determined, it is unclear whether these differences in sulphate concentration in the media indicate differences in rates of sulphide oxidation, or merely reflect differing rates of sulphate assimilation. Again, with the exception of cadmium the concentration of free metal in the medium did not generally increase, presumably because any metal released from the sulphides on oxidation was taken up by the fungi, or adsorbed on to their surface. It is unlikely therefore that these fungi could be effectively employed to leach metals from their sulphide ores.
From a solfataric field in Italy three isolates of spherical thermoacidophilic metal-mobilizing archaebacteria were obtained. They are facultative autotrophs. From sulfidic ores they extract metal ions with very high efficiency. They are also vigorous S°-oxidizers. Alternatively, they are able to use heterogeneous organic material such as yeast extract. The isolates grow within a temperature ränge from 50 to 80 °C. The
GC-content of their DNA is 45 mol %. No significant D N A homology is detectable between the isolates and the type strains of the members of the genera Acidianus and Sulfolobus. The DNA-dependent RNA Polymerase of isolate TH2 shows incomplete serological cross-reaction with antibodies against the enzyme of Sulfolobus acidocaldarius. On the basis of the distinct physiological and molecular properties we describe the new strains as members of the new genus Metallosphaera. Type species and type strain is Metallosphaera sedula (TH2, DSM5348).
From the shallow geothermally heated seafloor at the beach of Porto di Levante (Vulcano, Italy) 8 strains of long, tiny rods were isolated, which represent the first marine metal-mobilizing bacteria. Cells are Gram negative. They grow in a temperature range between 23 and 41°C with an optimum around 37°C at a salt concentration of up to 6.0% NaCl. The isolates are obligately chemolithotrophic, acidophilic aerobes which use sulfidic ores, elemental sulfur or ferrous iron as energy sources and procedure sulfuric acid. They show an upper pH-limit of growth at around 4.5. The G+C content of their DNA is around 64 mol%. Based on the results of the DNA-DNA hybridization they represent a new group within the genus Thiobacillus. Isolate LM3 is described as the type strain of the new species Thiobacillus prosperus.
A stable community of bacteria that had unusually high tolerance of soluble silver was isolated from soil by chemostat enrichment. The community consisted of three bacteria: Pseudomonas maltophilia, Staphylococcus aureus and a coryneform organism. The pseudomonas was primarly responsible for the silver resistance. The tolerance of high silver concentrations, up to 100 mM Ag+, was greatly reduced when the community was grown in the absence of silver. Pseudomonas maltophilia comprised approximately 50% by numbers of the community when grown in chemostats in the presence or absence of Ag+ but large fluctuations occurred in population sizes of the other two bacteria; the S. aureus population was small (less than 1%) in the presence of Ag+ but comparised a third of the total numbers when Ag+ was omitted from the medium. Silver-resistant respiration of the silveradapted community was significant even when it was confronted with high concentrations of Ag+. In contrast the respiration of the coryneform organism and particularly S. aureus was highly sensitive to silver. The inhibition constants for silver-sensitive respiration were 0.78 mM and 0.04 mM for silver acclimatized and nonacclimatized communities respectively.
The community had great capacity for silver bioaccumulation. Maximum concentrations of over 300 mg silver per g dry weight of biomass were recorded at an accumulation rate of 21 mg Ag+ h-1 (g biomass)-1. The extent of silver removal from solution was a function of initial concentration of silver; at low external concentrations (ca. 1 mM) all the silver was rapidly removed from solution, at high concentrations (ca. 12 mM) 84% removal occurred in 15 h.
The relative affinities of various cations for anionic sites in isolated, bacterial cell walls were assessed by means of a technique involving displacement of one cation by another. The affinity series determined was H+ greater than La3+ greater than Cd2+ greater than Sr2+ greater than Ca2+ greater than Mg2+ greater than K+ greater than Na+ greater than Li+. High affinity was correlated with low mobility of the bound ions in an electric field. The net cation-exchange capacities of walls isolated from a variety of bacteria were estimated by preparing the magnesium forms of the walls, washing them well with deionized water to remove supernumerary ions, and then completely displacing the magnesium with Na+ or H+. Total amounts of magnesium displaced varied from 73 mumol per gram dry weight, for walls of the teichoic acid-deficient 52A5 strain of Staphylococcus aureus to about 520 mumol per gram for Bacillus megaterium KM walls....
Mechanistic studies of the protonolytic carbon-mercury bond cleavage by organomercurial lyase from Escherichia coli (R831) suggest that the reaction proceeds via an SE2 pathway. Studies with stereochemically defined substrates cis-2-butenyl-2-mercuric chloride (1) and endo-norbornyl-2-mercuric bromide (2) reveal that a high degree of configurational retention occurs during the bond cleavage, while studies with exo-3-acetoxynortricyclyl-5-mercuric bromide (3) and cis-exo-2-acetoxy-bicyclo[2.2.1]hept-5-enyl-3-mercuric bromide (4) show that the protonolysis proceeds without accompanying skeletal rearrangement. Kinetic data for the enzymatic reactions of cis-2-butenyl-2-mercuric chloride (1) and trans-1-propenyl-1-mercuric chloride (6) indicate that these substrates show enhanced reaction rates of ca. 10-200-fold over alkylvinylmercurials and unsubstituted vinylmercurials, suggesting that the olefinic methyl substituent may stabilize an intermediate bearing some positive charge. Enzymatic reaction of 2-butenyl-1-mercuric bromide (5) yields a 72/23/5 mixture of 1-butene/trans-2-butene/cis-2-butene, indicative of intervening SE2' cleavage. The observation of significant solvent deuterium isotope effects at pH 7.4 of Vmax (H2O)/Vmax(D2O) = 2.1 for cis-2-butenyl-2-mercuric chloride (1) turnover and Vmax(H2O)/Vmax(D2O) = 4.9 for ethylmercuric chloride turnover provides additional support for a kinetically important proton delivery. Finally, the stoichiometric formation of butene and Hg(II) from 1 and methane and Hg(II) from methylmercuric chloride eliminates the possibility of an SN1 solvolytic mechanism. As the first well-characterized enzymatic reaction of an organometallic substrate and the first example of an enzyme-mediated SE2 reaction the organomercurial lyase catalyzed carbon-mercury bond cleavage provides an arena for investigating novel enzyme structure-function relationships.
Organomercurial lyase mediates the first of two steps in the microbial detoxification of organomercurial salts. This enzyme encoded on the plasmid R831 obtained from Escherichia coli J53-1 has been overproduced to the level of 3% of the soluble cell protein in E. coli by a construction using the T7 promoter. The enzyme has been purified to homogeneity in quantity in three steps. It is a monomer of Mr 22,400 with no detectable cofactors or metal ions. It catalyzes the protonolysis of the C-Hg bond in a wide range of organomercurial salts (primary, secondary, tertiary, alkyl, vinyl, allyl, and aryl) to the hydrocarbon and mercuric ion with turnover rates in the range of 1-240 min-1.
The compounds formed by the reaction of selenious acid with glutathione were studied with regard to the effects of pH and glutathione:selenious acid ratio. At ratios of 4:1 or less, and a pH below 2 and above 4, the first stable product is the selenotrisulfide derivative of glutathione (GSSeSG) plus an equimolar quantity of GSSG: 4GSH + H2SeO3 → GSSeSG + GSSG + 3H2O GSSeSG free of GSSG was prepared by separating the two compounds on a Dowex 50 column equilibrated with 0.01 M NiCl2 in 0.1 M sodium acetate (pH 4.7) followed by adsorption of the GSSeSG fraction to Dowex 50 Na+ at pH 3 and elution with ammonium acetate at pH 5.5. In order to determine the type of selenium compound formed under conditions more nearly simulating physiological conditions of pH and reactant concentrations, 75Se-labeled selenite (1 × 10-8 M) was treated with 4 × 10-3 M GSH at pH 7,25 °, followed by 50 mM iodoacetate. The major selenium compound thus formed was the Se-carboxymethyl derivative of glutathione selenopersulfide (GSSeH); this persulfide is believed to be formed by reduction of the initial selenotrisulfide product with excess GSH. Glutathione and elemental selenium were rapidly liberated from GSSeSG at pH 7 by 0.1 μg or less of highly purified glutathione reductase from yeast. The reduction of GSSeSG was not catalyzed by lipoyl dehydrogenase, nor was glutathione reductase active when DPNH or selenodicysteine (CySSeSCy) was substituted for TPNH or selenodiglutathione. The velocity of GSSeSG reduction was similar to that for GSSG reduction. Evidence was obtained that the initial reaction products were GSH and the selenopersulfide (GSSeH): GSSeSG + TPNH + H+ →glutathione reductase GSH + GSSeH + TPN+ The selenopersulfide rapidly decomposed to GSH and elemental selenium but could be trapped in the presence of 50 mM iodoacetate as the carboxymethylated derivative, which was identified by thin-layer electrophoresis, thin-layer chromatography, and gel filtration. It is believed that this work provides the first evidence for the selenopersulfide class of compounds. These reactions may have important applications to selenium metabolism and the mechanism of action of selenium as an essential nutrient.
A low-viscosity embedding medium based on ERL-4206 is recommended for use in electron microscopy. The composition is: ERL-4206 (vinyl cyclohexene dioxide) 10 g, D.E.R. 736 (diglycidyl ether of polypropylene glycol) 6 g, NSA (nonenyl succinic anhydride) 26 g, and S-1 (dimethylaminoethanol or DMAE) 0.4 g. The medium is easily and rapidly prepared by dispensing the components, in turn by weight, into a single flask. The relatively low viscosity of the medium (60 cP) permits rapid mixing by shaking and swirling. The medium is infiltrated into specimens after the use of any one of several dehydrating fluids, such as ethanol, acetone, dioxan, hexylene glycol, isopropyl alcohol, propylene oxide, and tert.-butyl alcohol. It is compatible with each of these in all proportions. After infiltration the castings are polymerized at 70°C in 8 hours. Longer curing does not adversely affect the physical properties of the castings. Curing time can be reduced by increasing the temperature or the accelerator, S-1, or both; and the hardness of the castings is controlled by changes in the D.E.R. 736 flexibilizer. The medium has a long pot life of several days and infiltrates readily because of its low viscosity. The castings have good trimming and sectioning qualities. The embedding matrix of the sections is very resistant to oxidation by KMnO4 and Ba(MnO4)2, compared with resins containing NADIC methyl anhydride. Sections are tough under the electron beam and may be used without a supporting membrane on the grids. The background plastic in the sections shows no perceptible substructure at magnifications commonly used for biological materials. The medium has been used successfully with a wide range of specimens, including endosperms with a high lipid content, tissues with hard, lignified cell walls, and highly vacuolated parenchymatous tissues of ripe fruits.
Selenious acid combines with cysteine, 2-mercaptoethanol, glutathione, or coenzyme A to form moderately stable derivatives having an enhanced absorption in the 260-380-mμ region. The combining ratio for the thiols and selenious acid was found to be 4:1 by spectrophotometric analysis. The over-all stoichiometry thus conforms to the reaction proposed by Painter (Painter, E. P. (1941), Chem. Rev. 28, 179), 4RSH + H2SeO3 → RSSeSR + RSSR + 3H2O. The reaction mixtures were resolved by thin-layer chromatography into two spots corresponding to the disulfide and the selenotrisulfide (RSSeSR). A column chromatographic procedure based on chelated copper as a stationary phase was developed which permitted the isolation of selenodicysteine and selenodimercaptoethanol. Selenodicysteine was identified by elemental analysis and by amino acid analysis. These results establish the above reaction as a plausible means of incorporating inorganic selenite into a stable organic moiety. The chemistry and possible biological significance of selenotrisulfides are under further investigation.
This chapter describes the ultrastructure, chemistry and function of the bacterial wall. Cell walls are dynamic and change to fulfill functions dictated by the cell in response to the environment. Most bacteria respond unequivocally to the Gram reaction; that is, some retain the large crystal violet-iodine complex (Gram-positive), whereas others are decolorized by the alcohol treatment (Gram-negative) and can be counterstained. Cell age, autolysin levels, and growth conditions can affect the Gram reaction. Unlike Gram-positive bacteria, freeze-cleaved and -etched Gram-negative cells present a number of cleavage sites within the wall that is an indication of multilayering. This wall is chemically and structurally more complex than its Gram-positive counterpart. Each of the layers of capsule, slime layers, and surface arrays reside above the wall and may be singular or in combination with one another. Each presents unique problems for preservation and visualization by electron microscopy. The chapter also discusses the functional aspects of walls that include (1) interaction with metals; (2) β-lactam drugs and low-level antibiotic resistance; and (3) functional discontinuities in the wall fabric.
The reaction of the FAD-containing enzyme, mercuric reductase, with NADPH has been studied by stopped-flow kinetic methods at 25 degrees C, pH 7.3. The results suggest that the reaction involves at least three steps. The first step is very rapid and is essentially complete within the dead time of the stopped-flow apparatus. This step is associated with decreasing absorbances at 340 nm (NADPH) and 455 nm (FAD), whereas there is little formation of the absorbance at 530 nm characterizing 2-electron-reduced enzyme subunits (EH2). The second step involves an increase of the absorbance at 530 nm. The third step results in an increase of the intensity of the long-wavelength band and a change of its shape. A second equivalent of NADPH per FAD is required for this step. It is proposed that the product is an EH2-NADPH complex. In addition to these rapid steps, slow absorbance changes are also observed.
A silver-resistant strain of Pseudomonas stutzeri was isolated from a silver mine. It harbored three plasmids, the largest of which (pKK1; molecular weight, 49.4 X 10(6)) specified silver resistance. Plasmid pKK1 was apparently nonconjugative but could be transferred to Pseudomonas putida by mobilization with plasmid R68.45.
The use of equilibrium dialysis techniques established that isolated cell walls of Bacillus subtilis possess selective affinities for several cations. The binding of these cations to the cell wall was influenced by the presence of various functional groups in the peptidoglycan matrix. Selective chemical modification of the free carboxyl and amino groups showed that when amino groups were replaced by neutral, bulky, or negatively charged groups, the sites available for cation complexing generally increased. Introduction of positive charges into the wall resulted in a marked decrease in the numbers of metal binding sites and usually a decrease in the apparent association constants. Both teichoic acid and peptidoglycan contribute to the sites available for interaction with metals. Hill plots of equilibrium dialysis data suggest that metal binding to cell walls involves negative cooperativity. Competition between various metals for binding sites suggested that the cations complex with identical sites on the cell walls. When the hydrogen ion concentration was increased, the affinity of the walls for metals decreased, but the numbers of metal binding sites remained constant, suggesting that cations and protons also compete for the same sites.