No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Bioremediation of a polymetallic, arsenic‐dominated reverse osmosis reject stream
Abstract
The treatment of metal‐laden industrial effluents by reverse osmosis is gaining in popularity worldwide due to its high performance. However, this process generates a polymetallic concentrate (retentate) stream in need of efficient post‐treatment prior to environmental discharge. This paper presents results on the bioremediation (in batch mode) of a metal‐laden, arsenic‐dominated retentate using Shewanella sp. O23S as inoculum. The incubation of the retentate for 14 days under anoxic conditions resulted in the following removal yields: As (8%), Co (11%), Mo (3%), Se (62%), Sb (30%), and Zn (40%). The addition of 1 mM cysteine increased the removal rate as follows: As (27%), Co (80%), Mo (78%), Se (88%), Sb (83%), and Zn (90%). The contribution of cysteine as a source of H2S to enhancing the removal yield was confirmed by its addition after seven days of incubations initially lacking it. Additionally, the cysteine‐sourced H2S was confirmed by its capture onto headspace‐mounted Pb‐acetate test strips that were analyzed by X‐ray diffraction. We show that real metal‐laden industrial effluents can be treated to medium‐to‐high efficiency using a biological system (naturally‐sourced inocula) and inexpensive reagents (yeast extract, lactate and cysteine).
Historically, sulfate-reducing bacteria (SRB) have been considered to be strict anaerobes, but reports in the past couple of decades indicate that SRB tolerate exposure to O2 and can even grow in aerophilic environments. With the transition from anaerobic to microaerophilic conditions, the uptake of Fe(III) from the environment by SRB would become important. In evaluating the metabolic capability for the uptake of iron, the genomes of 26 SRB, representing eight families, were examined. All SRB reviewed carry genes (feoA and feoB) for the ferrous uptake system to transport Fe(II) across the plasma membrane into the cytoplasm. In addition, all of the SRB genomes examined have putative genes for a canonical ABC transporter that may transport ferric siderophore or ferric chelated species from the environment. Gram-negative SRB have additional machinery to import ferric siderophores and ferric chelated species since they have the TonB system that can work alongside any of the outer membrane porins annotated in the genome. Included in this review is the discussion that SRB may use the putative siderophore uptake system to import metals other than iron.
Bacteria play crucial roles in the biogeochemical cycle of arsenic (As) and selenium (Se) as these elements are metabolized via detoxification, energy generation (anaerobic respiration) and biosynthesis (e.g. selenocysteine) strategies. To date, arsenic and selenium biomineralization in bacteria were studied separately. In this study, the anaerobic metabolism of As and Se in Shewanella sp. O23S was investigated separately and mixed, with an emphasis put on the biomineralization products of this process. Multiple analytical techniques including ICP-MS, TEM-EDS, XRD, Micro-Raman, spectrophotometry and surface charge (zeta potential) were employed. Shewanella sp. O23S is capable of reducing selenate (SeO42-) and selenite (SeO32-) to red Se(-S)0, and arsenate (AsO43-) to arsenite (AsO33-). The release of H2S from cysteine led to the precipitation of AsS minerals: nanorod AsS and granular As2S3. When As and Se oxyanions were mixed, both As-S and Se(-S)0 biominerals were synthesized. All biominerals were extracellular, amorphous and presented a negative surface charge (-24 to -38 mV). Kinetic analysis indicated the following reduction yields: SeO32- (90%), AsO43- (60%), and SeO42- (<10%). The mix of SeO32- with AsO43- led to a decrease in As removal to 30%, while Se reduction yield was unaffected (88%). Interestingly, SeO42- incubated with AsO43- boosted the Se removal (71%). The exclusive extracellular formation of As and Se biominerals might indicate an extracellular respiratory process characteristic of various Shewanella species and strains. This is the first study documenting a complex interplay between As and Se oxyanions: selenite decreased arsenate reduction, whereas arsenate stimulated selenate reduction. Further investigation needs to clarify whether Shewanella sp. O23S employs multi-substrate respiratory enzymes or separate, high affinity enzymes for As and Se oxyanion respiration.
Microbes form biominerals via biologically-controlled mineralization (BCM) and biologically-induced mineralization (BIM) (Konhauser and Riding, 2012). BCM is commonly an intracellular process, where microbes employ genetic determinants and enzymes to induce mineralization. The end product (the biomineral) of BCM serves a biological function for its host. Some notable examples include magnetotactic bacteria (the magnetite chain helps target microaerophilic environments) and bacteria that biomineralize carbonates (intracellular carbonate contributes to buoyant density) (Uebe and Schüler, 2016; Görgen et al., 2021). Conversely, mineral formation in BIM does not have a regulatory control and the biomineralization product is generally located outside the cell. Numerous minerals are being formed via this process such as BaSO4, PbS or iron minerals. BIM-produced biominerals do not often have a clear biological function. For instance, respiratory-sourced biogenic Se0 may contribute to the buoyant density of sludge granules in upflow bioreactors (Staicu and Barton, 2021). However, with the renewed interest in microbial biominerals new biological functions may be acknowledged in the future.
Acid mine drainage (AMD) still represents a huge environmental problem. Technical and scientific breakthroughs are still needed to decrease environmental damages, treatment cost, and waste production associated with AMD. The feasibility of combining continuously fed anaerobic sulfate-reducing bioreactor with downstream iron oxidation step was tested, at a laboratory scale, with two types of real arsenic-rich AMD waters from the site of Carnoulès (France), that differed in acidity (pH 3.3 and 4.0), arsenic (As, 18 and 174 mg.L⁻¹), and metal concentrations. Iron remained in solution, while up to 99% of As was precipitated as amorphous orpiment in the anaerobic sulfate-reducing bioreactor. Zinc (Zn) precipitation was also observed, up to 99%; however, the efficiency of Zn precipitation was less stable than that of As. The anaerobic bioreactor presented a stable bacterial community including a Desulfosporosinus-related sulfate reducer. When the effluents from the anaerobic process step were treated in a laboratory aerobic bioreactor, iron was oxidized efficiently. The feasibility of efficient orpiment bio-precipitation coupled with downstream iron oxidation was shown, thus opening the perspective of a low-cost combination of treatment steps for the removal of arsenic, zinc, and iron in As-rich AMDs.
Removal of heavy metal ions from wastewater is of prime importance for a clean environment and human health. Different reported methods were devoted to heavy metal ions removal from various wastewater sources. These methods could be classified into adsorption-, membrane-, chemical-, electric-, and photocatalytic-based treatments. This paper comprehensively and critically reviews and discusses these methods in terms of used agents/adsorbents, removal efficiency, operating conditions, and the pros and cons of each method. Besides, the key findings of the previous studies reported in the literature are summarized. Generally, it is noticed that most of the recent studies have focused on adsorption techniques. The major obstacles of the adsorption methods are the ability to remove different ion types concurrently, high retention time, and cycling stability of adsorbents. Even though the chemical and membrane methods are practical, the large-volume sludge formation and post-treatment requirements are vital issues that need to be solved for chemical techniques. Fouling and scaling inhibition could lead to further improvement in membrane separation. However, pre-treatment and periodic cleaning of membranes incur additional costs. Electrical-based methods were also reported to be efficient; however, industrial-scale separation is needed in addition to tackling the issue of large volume sludge formation. Electric- and photocatalytic-based methods are still less mature. More attention should be drawn to using real wastewaters rather than synthetic ones when investigating heavy metals removal. Future research studies should focus on ecofriendly, cost-effective, and sustainable materials and methods.
Microbes and metals are intricately linked in a complex relationship. Many microbial pathways rely on metals for functionality, including enzymatic machinery (co-factors in key enzymes), dissimilatory reduction in energy generation (as alternative electron acceptors in anaerobic respiration) and biomineralization. Some metals share very close physical–chemical properties, thus sensing and incorporating the right metal in enzymes can be a finely-tuned, tightly regulated process (Waldron and Robinson 2009). In environments where essential metals have limited bioavailability microbes have developed high-affinity chelators (metallophores) or are capable of changing the redox conditions at the microscale level to solubilize them. The production of cellular energy using the redox-state transformations of metals/metalloids is an ancient strategy some bacteria and archaea use to sustain growth under nutrient-poor and sometimes extreme conditions (Stolz and Oremland 1999; Gescher and Kappler 2012; Staicu and Barton 2017; Wells et al. 2020). Biominerals are synthesized by microbes to alleviate metal stress and to serve diverse ecological functions (e.g. magnetotactic bacteria synthesize particles of single-domain magnetite de novo, providing them the ability to sense and orient in the ambient geomagnetic field). Metals can be toxic and microbes have developed sophisticated resistance mechanisms to counteract this type of stress. Strategies include ion specific efflux pumps, sequestration in poorly soluble minerals and redox change reactions (Nies 1999; Ni et al. 2015).
Metals are also key to human health, culture and industrialization. The typical multivitamin supplements contain a host of metals including selenium, copper, nickel, zinc, manganese and molybdenum, again a reflection of the presence of metalloenzymes and their co-factors. Metals have played a crucial role in human history (e.g. iron age and bronze age), and today more than ever, our daily life cannot be sustained without metals, from energy production and storage, transport, building and maintaining infrastructure or to technology. Mobile phones, which have revolutionized how people communicate, contain iron, nickel, gold, silver, platinum, palladium, aluminum, tin and copper (Sullivan 2006). While some metals are still abundant, the projected demand for others will outstrip supply in the foreseeable future, thus being listed as critical raw materials (CRMs) by various agencies and by the European Commission (https://ec.europa.eu/). In contrast to the renewable energy, metals are not at a practical time scale, therefore their use should be sustainable. Further, there is growing concern over the proliferation of ‘e-waste’ (i.e. discarded electronic devices, computers and cell phones). This means new strategies have to be implemented for efficient recovery, reuse and for metal extraction from low-grade resources (e.g. metalliferous soils, metallurgical slags and mine waste; Vidal et al. 2017; Kisser et al. 2020). Microbes and their capacity to transport metals can be of great use in such a context as this approach offers a less energy-intensive and also a less environmentally-degrading alternative to processes such as hydro- and pyrometallurgy. Biomining and bioleaching, the recovery of metals using microbial metabolism, are successfully used in industrial operations for the extraction of copper, gold and uranium (Jerez 2017). This strategy can be applied to both metal-rich deposits as well as to low-grade metal wastes/slags resulted from past industrial activities and discarded in the environment (Potysz and Kierczak 2019). Another unexploited source is the metal-rich wastewater generated by numerous industrial activities. Such sources, in the framework of the growing circular economy paradigm shift, started to be regarded as a resource rather than a waste material. These industrial streams can be treated using a microbially-mediated bioremediation approach, coupled with metal recovery (Puyol et al. 2016). It may also be possible to recover metals from printed circuit boards of computers and cell phones (Argumedo-Delira, Diaz-Martinez and Gomez-Martinez 2020). Thus, we thought it timely to have a themed issue ‘Microbes vs Metals: Harvest and Recycle’.
We have assembled a group of papers with a range of topics covering various chemical elements such as antimony, arsenic, copper, gold, iron, lead, manganese, selenium, tellurium, thallium and alloys (steel). They include contributions on metal resistance (Cyriaque et al. 2020; Sanyal, Reith and Shuster 2020; Yasir et al. 2020; Butz et al. 2021; Xu et al. 2020), biomineralization (Staicu et al. 2020), microbial ecology (Sjöberg et al. 2020; Taleski et al. 2020; Garrison and Field 2021; Zhang et al. 2021), as well as several review articles (Oremland 2020; Wells and Stolz 2020; Giachino et al. 2021; Mergeay and van Houdt 2021). Overall, the above-mentioned contributions demonstrate the complex relationship microbes have with chemically-diverse elements from the periodic table, from transition and precious metals to metalloids and alloys. Either as pure cultures or as mixed microbial communities, microbes are able to colonize and modify diverse environments, thus impacting the mobility and biogeochemical cycles of the elements in nature. From a technological perspective, microbes act as cleaning agents in industrially-polluted environments, being exploited in approaches that are less aggressive than the conventional treatment systems.
This themed issue is also dedicated to one of the pioneers of geomicrobiology, Professor Henry L. Ehrlich, whom we lost in 2020. Professor Ehrlich was known not only as an expert in microbial manganese metabolism, but also a great mentor, teacher and source of inspiration (Ghiorse 2020).
Nanoscale Zero-Valent Iron (nZVI) is a cost-effective nanomaterial that is widely used to remove a broad range of metal(loid)s and organic contaminants from soil and groundwater. In some cases, this material alters the taxonomic and functional composition of the bacterial communities present in these matrices; however, there is no conclusive data that can be generalized to all scenarios. Here we studied the effect of nZVI application in situ on groundwater from the site of an abandoned fertilizer factory in Asturias, Spain, mainly polluted with arsenic (As). The geochemical characteristics of the water correspond to a microaerophilic and oligotrophic environment. Physico-chemical and microbiological (cultured and total bacterial diversity) parameters were monitored before and after nZVI application over six months. nZVI treatment led to a marked increase in Fe(II) concentration and a notable fall in the oxidation-reduction potential during the first month of treatment. A substantial decrease in the concentration of As during the first days of treatment was observed, although strong fluctuations were subsequently detected in most of the wells throughout the six-month experiment. The possible toxic effects of nZVI on groundwater bacteria could not be clearly determined from direct observation of those bacteria after staining with viability dyes. The number of cultured bacteria increased during the first two weeks of the treatment, although this was followed by a continuous decrease for the following two weeks, reaching levels moderately below the initial number at the end of sampling, and by changes in their taxonomic composition. Most bacteria were tolerant to high As(V) concentrations and showed the presence of diverse As resistance genes. A more complete study of the structure and diversity of the bacterial community in the groundwater using automated ribosomal intergenic spacer analysis (ARISA) and sequencing of the 16S rRNA amplicons by Illumina confirmed significant alterations in its composition, with a reduction in richness and diversity (the latter evidenced by Illumina data) after treatment with nZVI. The anaerobic conditions stimulated by treatment favored the development of sulfate-reducing bacteria, thereby opening up the possibility to achieve more efficient removal of As.
The repurposing of by-products and the reduction of waste from food processing streams is an ever-increasing area of interest. Brewer’s spent yeast (BSY) is a prevalent by-product of the brewing industry. The spent yeast cells are removed at the end of the bulk fermentation. A small amount of it is used to start the next batch of fermentation; however, the majority of the spent yeast is discarded. This discarded yeast is high in nutrients, in particular proteins, vitamins and minerals, as well as containing functional and biologically active compounds such as polyphenols, antioxidants, β-glucans and mannoproteins. At present, BSY is mainly used in animal feed as a cheap and readily available source of protein. This review explores alternative, value-added applications for brewer’s spent yeast including nutritional ingredients, functional food additives as well as non-food applications. A major challenge in the utilization of BSY in food for human consumption is the high level of RNA. An excess of RNA in the diet can lead to an increase in uric acid in the bloodstream, potentially causing painful health conditions like gout. This issue can be overcome by RNA degradation and removal via additional treatment, namely heat treatment and enzymatic treatment. There is potential for the use of BSY ingredients in various food applications, including meat substitutes, bakery products and savory snacks.
Bacillus sp. Abq, belonging to Bacillus cereus sensu lato, was isolated from an aquifer in New Mexico, USA and phylogenetically classified. The isolate possesses the unusual property of precipitating Pb(II) by using cysteine, which is degraded intracellularly to hydrogen sulfide (H2S). H2S is then exported to the extracellular environment to react with Pb(II), yielding PbS (galena). Biochemical and growth tests showed that other sulfur sources tested (sulfate, thiosulfate, and methionine) were not reduced to hydrogen sulfide. Using equimolar concentration of cysteine, 1 mM of soluble Pb(II) was removed from Lysogeny Broth (LB) medium within 120 h of aerobic incubation forming black, solid PbS, with a removal rate of 2.03 µg L-1 h-1 (∼8.7 µM L-1 h-1). The mineralogy of biogenic PbS was characterized and confirmed by XRD, HRTEM, and EDX. Electron microscopy and electron diffraction identified crystalline PbS nanoparticles with a diameter <10 nm, localized in the extracellular matrix and on the surface of the cells. This is the first study demonstrating the use of cysteine in Pb(II) precipitation as insoluble PbS and it may pave the way to PbS recovery from secondary resources, such as Pb-laden industrial effluents.
Coal-fired power facilities generate a polymetallic effluent (Flue Gas Desulfurization-FGD) rich in sulfate. FGD effluents may be considered an important secondary resource. This paper investigates the recovery of sulfate as barite (BaSO4), a mineral with high commercial value and a critical raw material. Using equimolar BaCl2, >99% desulfurization of an FGD effluent produced by a coal-fired power plant operating in central Poland was achieved, yielding up to 16.5 kg high purity barite m−3. The recovered barite was characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TGA), scanning electron microscopy analysis (SEM), surface properties (PZC), density, and chemical stability (TCLP), and was compared with a commercial reference material. Barite recovery also led to the reduction in concentration of Al (86%), Cu (52%), K (69%), Mo (62%), Se (40%), Sr (91%), and U (75%) initially present in the FGD effluent. TCLP results indicate the entrapment and the stabilization of ~70% Se and ~90% Al in the barite structure. Based on this dataset, an in-depth characterization of the recovered barite is presented, and the removal mechanism of the elements is discussed. The study also provides a preliminary cost benefit analysis of the process. To our best knowledge, this is the first work showing barite recovery and metal removal from FGD effluents using a one-step process.
In contrast to aerobic organisms, strictly anaerobic microorganisms require the absence of oxygen and usually a low redox potential to initiate growth. As oxygen is ubiquitous in air, retaining O2-free conditions during all steps of cultivation is challenging but a prerequisite for anaerobic culturing. The protocol presented here demonstrates the successful cultivation of an anaerobic mixed culture derived from a biogas plant using a simple and inexpensive method. A precise description of the entire anoxic culturing process is given including media preparation, filling of cultivation flasks, supplementation with redox indicator and reducing agents to provide low redox potentials as well as exchanging the headspace to keep media free from oxygen. Furthermore, a detailed overview of aseptically inoculating gas tight serum flasks (by using sterile syringes and needles) and suitable incubation conditions is provided. The present protocol further deals with gas and liquid sampling for subsequent analyses regarding gas composition and volatile fatty acid concentrations using gas chromatography (GC) and high performance liquid chromatography (HPLC), respectively, and the calculation of biogas and methane yield considering the ideal gas law.
Shewanella sp. O23S is a dissimilatory arsenate reducing bacterial strain involved in arsenic transformations within the abandoned gold mine in Zloty Stok (SW Poland). Previous physiological studies revealed that O23S may not only release arsenic from minerals, but also facilitate its immobilization through co-precipitation with reduced sulfur species. Given these uncommon, complementary characteristics and the application potential of the strain in arsenic-removal technologies, its genome (~5.3 Mbp), consisting of a single chromosome, two large plasmids (pSheA and pSheB) and three small plasmid-like phages (pSheC-E) was sequenced and annotated. Genes encoding putative proteins involved in heavy metal transformations, antibiotic resistance and other phenotypic traits were identified. An in-depth comparative analysis of arsenic respiration (arr) and resistance (ars) genes and their genetic context was also performed, revealing that pSheB carries the only copy of the arr genes, and a complete ars operon. The plasmid pSheB is therefore a unique natural vector of these genes, providing the host cells arsenic respiration and resistance abilities. The functionality of the identified genes was determined based on the results of the previous and additional physiological studies, including: the assessment of heavy metal and antibiotic resistance under various conditions, adhesion-biofilm formation assay and BiologTM metabolic preferences test. This combined genetic and physiological approach shed a new light on the capabilities of O23S and their molecular basis, and helped to confirm the biosafety of the strain in relation to its application in bioremediation technologies.
Background:Megasphaera elsdenii is an ecologically important rumen bacterium that metabolizes lactate and relieves rumen acidosis (RA) induced by a high-grain-diet. Understanding the regulatory mechanisms of the lactate metabolism of this species in RA conditions might contribute to developing dietary strategies to alleviate RA.
Methods:Megasphaera elsdenii was co-cultured with four lactate producers (Streptococcus bovis, Lactobacilli fermentum, Butyrivibrio fibrisolvens, and Selenomonas ruminantium) and a series of substrate starch doses (1, 3, and 9 g/L) were used to induce one normal and two RA models (subacute rumen acidosis, SARA and acute rumen acidosis, ARA) under batch conditions. The associations between bacterial competition and the shift of organic acids’ (OA) accumulation patterns in both statics and dynamics manners were investigated in RA models. Furthermore, we examined the effects of substrate lactate concentration and pH on Megasphaera elsdenii’s lactate degradation pattern and genes related to the lactate utilizing pathways in the continuous culture.
Results and Conclusion: The positive growth of M. elsdenii and B. fibrisolvens caused OA accumulation in the SARA model to shift from lactate to butyrate and resulted in pH recovery. Furthermore, both the quantities of substrate lactate and pH had remarkable effects on M. elsdenii lactate utilization due to the transcriptional regulation of metabolic genes, and the lactate utilization in M. elsdenii was more sensitive to pH changes than to the substrate lactate level. In addition, compared with associations based on statics data, associations discovered from dynamics data showed greater significance and gave additional explanations regarding the relationships between bacterial competition and OA accumulation.
The use of yeast extracts as a natural and valuable additive ingredient intended for the production of functional food and dietary supplements were demonstrated. Te chemical composition, amino acid analysis, determination of protein molecular weights, antioxidant properties, and sensory evaluation were carried out for two yeast extracts. It was found that the tested extracts are characterised by high essential amino acid content, exceeding the levels of reference protein developed by the FAO/WHO, and high antioxidant activity. Sensory characteristics of tested extracts may favourably influence the quality of the proposed functional foods and dietary supplements. Te obtained results indicate that the tested extracts can be utilised as a source of free amino acids and peptides in the design of functional foods and dietary supplements.
The purpose of this study was a detailed characterization of Shewanella sp. O23S, a strain involved in arsenic transformation in ancient gold mine waters contaminated with arsenic and other heavy metals. Physiological analysis of Shewanella sp. O23S showed that it is a facultative anaerobe, capable of growth using arsenate, thiosulfate, nitrate, iron or manganite as a terminal electron acceptor, and lactate or citrate as an electron donor. The strain can grow under anaerobic conditions and utilize arsenate in the respiratory process in a broad range of temperatures (10-37 °C), pH (4-8), salinity (0%-2%), and the presence of heavy metals (Cd, Co, Cr, Cu, Mn, Mo, Se, V and Zn). Under reductive conditions this strain can simultaneously use arsenate and thiosulfate as electron acceptors and produce yellow arsenic (III) sulfide (As2S3) precipitate. Simulation of As-removal from water containing arsenate (2.5 mM) and thiosulfate (5 mM) showed 82.5% efficiency after 21 days of incubation at room temperature. Based on the obtained results, we have proposed a model of a microbially mediated system for self-cleaning of mine waters contaminated with arsenic, in which Shewanella sp. O23S is the main driving agent.
Raman, depolarization, and infrared spectra of the glass, liquid, and
gaseous disordered phases of As2O3 have been
studied at temperatures between 4.5 and 1200 K. Spectra recorded at
temperatures in the range of the glass-liquid transition indicate that
the microstructures of the glass and liquid are quite similar near
Tg and can best be characterized as distorted layerlike
remnants of the monoclinic crystalline phase, claudetite. Our results
have been contrasted to corresponding results for
As2S3 and As2Se3 and have
been compared with the predictions of current models of the structure of
As2X3-type glasses. The observed spectra are most
compatible with the composite model which combines aspects of the layer
and molecular models. No evidence is found to support the conjecture of
Taylor, Bishop, and Mitchell that for layer-type
As2X3 glasses a characteristic temperature
Ts exists such that Ts>Tg and the
layers catastrophically disintegrate at temperatures T>Ts.
The temperature dependence of the Raman shift, full width at
half-maximum (Γ12), and integrated intensity of the
376-cm-1 band associated with the symmetric stretching mode
of the As-O-As linkage have been studied as have the shifts with
temperature of other prominent spectral features. We find that the glass
transition temperature can be accurately determined from a plot of
lnΓ12 vs ln(1000T) and that above Tg
Γ12(376 cm-1)~T12. The
temperature dependence of the ν1 and ν3
modes of the AsO3 pyramidal unit indicates that the apex
angle decreases with increasing temperature. The low-frequency (8-30
cm-1) region of the Raman spectrum of vitreous
As2O3 has been carefully studied at 11.4 K. From
the reduced Raman spectrum of the low-frequency region it is found that
the product of the frequency-dependent coupling coefficient C(ω)
and the density of vibrational states g(ω) varies as
ω2.5.
DOI:https://doi.org/10.1103/PhysRevB.14.1781
Cysteine desulfurase is a pyridoxal 5'-phosphate (PLP)-dependent homodimeric enzyme that catalyzes the conversion of L-cysteine to L-alanine and sulfane sulfur via the formation of a protein-bound cysteine persulfide intermediate on a conserved cysteine residue. Increased evidence for the functions of cysteine desulfurases has revealed their important roles in the biosyntheses of Fe-S clusters, thiamine, thionucleosides in tRNA, biotin, lipoic acid, molybdopterin, and NAD. The enzymes are also proposed to be involved in cellular iron homeostasis and in the biosynthesis of selenoproteins. The mechanisms for sulfur mobilization mediated by cysteine desulfurases are as yet unknown, but enzymes capable of providing a variety of biosynthetic pathways for sulfur/selenium-containing biomolecules are probably applicable to the production of cofactors and the bioconversion of useful compounds.
Glutathione (GSH) and its derivative phytochelatin are important binding factors in transition-metal homeostasis in many eukaryotes.
Here, we demonstrate that GSH is also involved in chromate, Zn(II), Cd(II), and Cu(II) homeostasis and resistance in Escherichia coli. While the loss of the ability to synthesize GSH influenced metal tolerance in wild-type cells only slightly, GSH was important
for residual metal resistance in cells without metal efflux systems. In mutant cells without the P-type ATPase ZntA, the additional
deletion of the GSH biosynthesis system led to a strong decrease in resistance to Cd(II) and Zn(II). Likewise, in mutant cells
without the P-type ATPase CopA, the removal of GSH led to a strong decrease of Cu(II) resistance. The precursor of GSH, γ-glutamylcysteine
(γEC), was not able to compensate for a lack of GSH. On the contrary, γEC-containing cells were less copper and cadmium tolerant
than cells that contained neither γEC nor GSH. Thus, GSH may play an important role in trace-element metabolism not only in
higher organisms but also in bacteria.
Selenium (Se) respiration in bacteria was revealed for the first time at the end of 1980s. Although thermodynamically-favorable, energy-dense and documented in phylogenetically-diverse bacteria, this metabolic process appears to be accompanied by a number of challenges and numerous unanswered questions. Selenium oxyanions, SeO4²⁻ and SeO3²⁻, are reduced to elemental Se (Se⁰) through anaerobic respiration, the end product being solid and displaying a considerable size (up to 500 nm) at the bacterial scale. Compared to other electron acceptors used in anaerobic respiration (e.g. N, S, Fe, Mn, and As), Se is one of the few elements whose end product is solid. Furthermore, unlike other known bacterial intracellular accumulations such as volutin (inorganic polyphosphate), S⁰, glycogen or magnetite, Se⁰ has not been shown to play a nutritional or ecological role for its host. In the context of anaerobic respiration of Se oxyanions, biogenic Se⁰ appears to be a by-product, a waste that needs proper handling, and this raises the question of the evolutionary implications of this process. Why would bacteria use a respiratory substrate that is useful, in the first place, and then highly detrimental? Interestingly, in certain artificial ecosystems (e.g. upflow bioreactors) Se⁰ might help bacterial cells to increase their density and buoyancy and thus avoid biomass wash-out, ensuring survival. This review article provides an in-depth analysis of selenium respiration (model selenium respiring bacteria, thermodynamics, respiratory enzymes, and genetic determinants), complemented by an extensive discussion about the evolutionary implications and the properties of biogenic Se⁰ using published and original/unpublished results.
Here, we show that high permeability and good fouling resistance can save substantial energy and maximize freshwater output for reverse osmosis (RO) desalination of low-salinity wastewater, via both theoretical and experimental demonstrations. First, module-scale modelling revealed that at reasonably low feed salinity, the specific energy consumption (SEC) drops by > 60% when water permeability is increased from 2 to 7 L m⁻² hr⁻¹ bar⁻¹. Optimization of different operating parameters was further performed to maximize the energy efficiency and process capacity, and suitable salt rejection to maintain permeate quality was evaluated. Next, we synthesized zwitterionic copolymers of different molecular weight and fabricated hollow fiber membranes with a pure water permeability of 8.6 L m⁻² hr⁻¹ bar⁻¹, 98.5% rejection to NaCl, and excellent fouling resistance. 85% water recovery, 56% energy saving and 25% reduction of membrane area were demonstrated for treating membrane bioreactor (MBR) filtrate from a local water reclamation plant.
Dowsing for danger
Arsenic is a metabolic poison that is present in minute quantities in most rock materials and, under certain natural conditions, can accumulate in aquifers and cause adverse health effects. Podgorski and Berg used measurements of arsenic in groundwater from ∼80 previous studies to train a machine-learning model with globally continuous predictor variables, including climate, soil, and topography (see the Perspective by Zheng). The output global map reveals the potential for hazard from arsenic contamination in groundwater, even in many places where there are sparse or no reported measurements. The highest-risk regions include areas of southern and central Asia and South America. Understanding arsenic hazard is especially essential in areas facing current or future water insecurity.
Science , this issue p. 845 ; see also p. 818
Severe effects of selenium (Se) occurred among birds feeding and nesting at Kesterson Reservoir (San Joaquin Valley, California) in 1983‐1985. This paper describes the integration of site monitoring, risk assessment, and management actions conducted after the effects of Se were discovered. Selenium contamination of the site occurred over just a few years, but actions to resolve the contamination issues required >20 years. The Reservoir, a series of 12 ponds totaling about 1,280 acres (518 hectares), served for storage and evaporation of subsurface agricultural drainage. Selenium concentrations in Reservoir inflow in 1983 were about 300 µg/L, primarily as selenate; within the ponds it was biogeochemically reduced to other inorganic and organic forms and bioaccumulated by biota or deposited to sediments. An estimated 9000 kg of Se were delivered to Kesterson in 1981‐1986. A 1985 order required cleanup and abatement of the Reservoir, so Reclamation and the US Department of the Interior undertook actions and studies to reduce hazards to birds. In 1988, about one million cubic yards (764,500 cubic meters) of soil were used to fill portions of the Reservoir, transforming it into terrestrial habitat. Intensive monitoring began in 1989 to assess the impact of the Reservoir on wildlife, provide a basis for adjusting site management, verify the effectiveness of cleanup actions, and provide a basis for modifying future monitoring. Monitoring continued until 2014, with modifications and management actions based on results of two risk assessments (1993 and 2000). Monitoring results in 2013‐2014 showed that Se concentrations were relatively stable over time and risks to wildlife were low. From the initial problem discovery to the conclusion of actions taken to remediate the site, combining responsive, reactive, and adaptive monitoring; modeling; risk assessment, and mitigation actions proved effective in solving the problem so that risks to wildlife were reduced to minimal levels. This article is protected by copyright. All rights reserved. Because severe effects of selenium (Se) occurred in birds at Kesterson Reservoir, portions of the Reservoir were filled with soil, transforming it into terrestrial habitat; we describe the integration of subsequent site monitoring, ecological risk assessment, and management actions. Monitoring in 1989-2014 and two risk assessments (1993 and 2000) assessed impacts on wildlife and provided a basis for adjusting site management and modifying future monitoring; final results showed that Se concentrations were relatively stable over time and risks to wildlife were low. From the initial problem discovery to the conclusion of actions taken to remediate the site, combining responsive, reactive, and adaptive monitoring; modeling; and mitigation actions proved effective in solving the problem so that risks to wildlife were reduced to minimal levels. Selenium contamination of the site occurred over just a few years, but actions to resolve the contamination issues required more than 20 years.
A significant amount of antimony (Sb) enters into the environment every year because of the wide use of Sb compounds in industry and agriculture. The exposure to Sb, either direct consumption of Sb or indirectly, may be fatal to the human health because both antimony and antimonide are toxic. Firstly, the introduction of Sb chemistry, distribution and health threats are presented in this review, which is essential to the removal techniques. Then, we provide the recent and common techniques to remove Sb, including adsorption, coagulation/flocculation, membrane separation, electrochemical methods, ion exchange and extraction. Removal techniques concentrate on the advantages, drawbacks, economical efficiency and the recent achievements of each technique. We also take an overall consideration of experimental conditions, comparison criteria, and economic aspects.
Oxyanions of arsenic and selenium call be used in microbial anaerobic respiration as terminal electron accepters. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram-positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used Varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated.
The chapter considers basic aspects of chemical thermodynamics as relevant for understanding microbial metabolisms in nature and for defining the chemical environments of the microbial world. The chapter describes enthalpy, entropy, and Gibbs free energy. All thermodynamically favorable chemical reactions proceed, barring kinetic barriers, until the distribution of reacting components in the system reaches equilibrium. The chapter discusses influence of temperature on thermodynamic properties, activity coefficient calculations, gas solubility and Henry's law, oxidation-reduction reactions. Cellular architecture and its relationship to show how organisms gain energy for their growth and metabolism are discussed. The chapter examines how catabolic (also called dissimilatory) processes and light provide the energy for the anabolic (also called assimilatory) synthesis of cellular material. It discusses some of the basic aspects of cellular metabolism and explains how different metabolisms are named. A vast array of different energy-providing metabolisms exist in nature, and a common nomenclature is adopted whereby these metabolisms are named based on their (1) energy source, (2) electron source, and (3) carbon source.
Infrared absorption and polarized Raman spectra of monoclinic As2O3 at 300K and 7K have been recorded. A vibrational analysis of the AsO bond stretching. OAsO angle deformation and of the rigid layer modes is reported. A complete valence force field calculation states precisely the assignments. The values of some force constants in crystalline and disordered phases of AS2O3 are compared.
The molecular species of As(III) in aqueous solution have been studied by the Raman effect. Utilizing the Job method of continuous variation, solutions with [OH-]/[As(III)] between 3.5 and 15 have been shown to contain the four species As(OH)3, AsO(OH)2-, AsO2(OH)2-, and AsO33-. The Raman spectra are consistent with a C3v point group assignment for both As(OH)3 and AsO33-. Cs symmetry has been shown for AsO(OH)2- and probably for AsO2(OH)2-, although experimental data on the latter species were most difficult to obtain, since the spectra of all species are overlapped to a large extent. The As-O stretching vibrations, insensitive to D2O, are between 790 and 750 cm-1, whereas the symmetric As-OH stretching modes, all exhibiting an isotope effect, are at 710 cm-1 for As(OH)3 and 570 cm-1 for AsO(OH)2-. The species As(OH)3 is also identified from its Raman spectrum as the only major component in acidic aqueous solutions of As4O6(s). The existence of HAsO2 is ruled out. Furthermore, there is no evidence for polymerization in basic solutions within an [As(III)] range of 0.6-5.0 M.
A 600 ml continuously stirred tank reactor was used to assess the performance of a zinc sulfide precipitation process using a biogenic sulfide solution (the effluent of a sulfate-reducing bioreactor) as sulfide source. In all experiments, a proportional-integral (PI) control algorithm was used to control the pH and the sulfide (S2-) concentration at the desired level in the precipitator. The pS (defined as: -log [S2-]) and pH were optimised using a chemical Na2S solution as sulfide source. A S2- concentration of 10(-15) M (i.e. pS 15) was found to be optimal for zinc sulfide precipitation, resulting in a residual zinc concentration of 0.07 mg/l from a 3 g/l Zn2+ influent, for both chemical Na2S and biogenic sulfide solutions. The mean particle size of the ZnS precipitates at pS 15 and pH 6.3 was 7.5 and 10.2 mu m when using biogenic sulfide and chemical Na2S, respectively, indicating that both sulfide sources are adequate for solid-liquid separation by sedimentation. When biogenic sulfide instead of chemical Na2S was used, the efficiency of the ZnS precipitation process slightly decreased both in terms of zinc effluent concentration (at pS 10 and 20) and particle size of the precipitate (at pS 10, 15 and 20). This was shown to be attributed to the presence of various substances (phosphate, micro-nutrients, acetate, EDTA) present in the sulfate-reducing reactor effluent. (C) 2006 Elsevier B.V. All rights reserved.
Copper was continuously and selectively precipitated with Na(2)S to concentrations below 0.3 ppb from water containing around 600 ppm of both Cu and Zn in a Continuously Stirred Tank Reactor. The pH was controlled at 3 and the pS at 25 (pS=-log(S(2-))) by means of an Ag(2)S sulfide selective electrode. Copper's recovery and purity were about 100%, whereas the total soluble sulfide concentration was below 0.02 ppm. X-ray diffraction (XRD) analysis showed that copper precipitated as hexagonal CuS (covellite). The mode of the particle size distribution (PSD) of the CuS precipitates was around 36 microm. The PSD increased by high pS values and by the presence of Zn. Depending on the turbulence, the CuS precipitates can grow up to 200 microm or fragment in particles smaller than 3 microm in a few seconds. Zn precipitation with Na(2)S at pH 3 and 4, in batch, always lead to Zn concentrations above 1 ppm. Zn precipitated as cubic ZnS (spharelite).
A newly discovered arsenate-reducing bacterium, strain OREX-4, differed significantly from strains MIT-13 and SES-3, the previously described arsenate-reducing isolates, which grew on nitrate but not on sulfate. In contrast, strain OREX-4 did not respire nitrate but grew on lactate, with either arsenate or sulfate serving as the electron acceptor, and even preferred arsenate. Both arsenate and sulfate reduction were inhibited by molybdate. Strain OREX-4, a gram-positive bacterium with a hexagonal S-layer on its cell wall, metabolized compounds commonly used by sulfate reducers. Scorodite (FeAsO42. H2O) an arsenate-containing mineral, provided micromolar concentrations of arsenate that supported cell growth. Physiologically and phylogenetically, strain OREX-4 was far-removed from strains MIT-13 and SES-3: strain OREX-4 grew on different electron donors and electron acceptors, and fell within the gram-positive group of the Bacteria, whereas MIT-13 and SES-3 fell together in the epsilon-subdivision of the Proteobacteria. Together, these results suggest that organisms spread among diverse bacterial phyla can use arsenate as a terminal electron acceptor, and that dissimilatory arsenate reduction might occur in the sulfidogenic zone at arsenate concentrations of environmental interest. 16S rRNA sequence analysis indicated that strain OREX-4 is a new species of the genus Desulfotomaculum, and accordingly, the name Desulfotomaculum auripigmentum is proposed.
Oxyanions of arsenic and selenium can be used in microbial anaerobic respiration as terminal electron acceptors. The detection of arsenate and selenate respiring bacteria in numerous pristine and contaminated environments and their rapid appearance in enrichment culture suggest that they are widespread and metabolically active in nature. Although the bacterial species that have been isolated and characterized are still few in number, they are scattered throughout the bacterial domain and include Gram-positive bacteria, beta, gamma and epsilon Proteobacteria and the sole member of a deeply branching lineage of the bacteria, Chrysiogenes arsenatus. The oxidation of a number of organic substrates (i.e. acetate, lactate, pyruvate, glycerol, ethanol) or hydrogen can be coupled to the reduction of arsenate and selenate, but the actual donor used varies from species to species. Both periplasmic and membrane-associated arsenate and selenate reductases have been characterized. Although the number of subunits and molecular masses differs, they all contain molybdenum. The extent of the environmental impact on the transformation and mobilization of arsenic and selenium by microbial dissimilatory processes is only now being fully appreciated.
Selenium pollution is a worldwide phenomenon and is associated with a broad spectrum of human activities, ranging from the most basic agricultural practices to the most high-tech industrial processes. Consequently, selenium contamination of aquatic habitats can take place in urban, suburban, and rural settings alike--from mountains to plains, from deserts to rainforests, and from the Arctic to the tropics. Human activities that increase waterborne concentrations of selenium are on the rise and the threat of widespread impacts to aquatic life is greater than ever before. Important sources of selenium contamination in aquatic habitats are often overlooked by environmental biologists and ecological risk assessors due to preoccupation with other, higher priority pollutants, yet selenium may pose the most serious long-term risk to aquatic habitats and fishery resources. Failure to include selenium in the list of constituents measured in contaminant screening/monitoring programs is a major mistake, both from the hazard assessment aspect and from the pollution control aspect. Once selenium contamination begins, a cascade of bioaccumulation events is set into motion which makes meaningful intervention nearly impossible. However, this cascade of events need not happen if adequate foresight and planning are exercised. Early evaluation and action are key. Prudent risk management based on environmentally sound hazard assessment and water quality goals can prevent biological impacts.