[Show abstract][Hide abstract] ABSTRACT: Recently, nanoscience has become one of the most promising fields of research with greater impact on economy and environment health. The research on nanomaterials: materials of 100 nm in at least one dimension, is likely to result in the production of huge number of new nano-products in the coming years. Considering the importance of nanotechnology, a greater attention has been paid on this industry which is expected to reach a market size of approximately 2.6 trillion dollars by 2015 . In addition, nanotechnology is also likely to influence agricultural research especially in (i) the conversion of agricultural and food wastes to energy and other useful by-products through enzymatic nano-bio-processing (ii) disease prevention and treatment of plants using various nanomaterials  and (iii) reproductive science and technology. Despite these benefits, the increasing numbers of commercial products, from cosmetics to medicine and fertilizers to crop products are adding sufficient amounts of nanomaterials ultimately to soils. Such nanoparticles have however, been found highly resistant to degradation and persist in soil or water bodies. Nanomaterials for example carbon nanotubes [3, 4], graphene-based nanomaterials , iron-based nanoparticles , silver  and copper, zinc and titanium oxide nanoparticles [8, 9] have been reported to cause biologically undesirable toxic effects on both deleterious and beneficial rhizosphere microorganisms [10-12] including Escherichia coli, Bacillus subtilis, and Streptococcus aureus , Pseudomonas chlororaphis [14-18], Pseudomonas putida  and Campylobacter jejuni . However, the reports on the effect of nanoparticles on secondary metabolites of microbes are conflicting. For example, Dimkpa et al.  in a recent study found that sub-lethal levels of CuONPs reduced the secretion of plant growth promoting substance siderophore in P. chlororaphis O6 whereas ZnO NPs increased the production of the fluorescent siderophore pyoverdine. Similarly, a contrasting effect of CuO and ZnO NPs on siderophores and IAA has also been reported by Dimpka et al.  suggesting that the effect of NPs on secondary metabolite production by bacterial populations cannot be generalized rather it is highly metabolite/nano specific and may vary from Symbiotic nitrogen fixing rhizobia besides fixing atmospheric nitrogen also produces plant growth promoting substances such as indole acetic acids, siderophores, and cyanogenic compounds etc. However, the effects of nanomaterials on plant growth regulating substances synthesized by these bacteria are not reported. In this paper we have examined the impact of varying concentration of three metal oxide nanoparticles (MONPs) namely copper oxide (CuO), iron oxide (Fe2O3) and zinc oxide (ZnO) on growth behaviour and plant growth promoting activities of nodule forming bacterium Rhizobium sp. strain OS1. The three MONPs tested in this study differentially affected the levels of plant growth regulating substances in a dose dependent manner which varied with species of each nanoparticle. A maximum reduction in indole acetic acid, hydrogen cyanide, ammonia and siderophores, expressed by Rhizobium sp. OS1 was observed at 150 µgml-1 each of CuO, Fe2O3 and ZnO. Iron oxide did not show any toxicity to siderophores. At 50 µgml
[Show abstract][Hide abstract] ABSTRACT: Phosphate-solubilizing microorganisms (PSM) including bacteria, fungi, and actinomycetes dwelling in soil or other environment, for example, rhizosphere, do play some vital roles in facilitating growth and development of legumes and cereal plants via one or simultaneous mechanisms. Phosphate-solubilizing microbes when applied in agricultural practices provide one of the major plant nutrients, phosphorus, to plants by transforming insoluble P into soluble and plant available forms. This practice of applying PSM for enhancing legumes and cereal production has been found inexpensive and in many cases a successful strategy of reducing fertilizer input in intensive agricultural practices. The advent of such an eco-friendly option in farming system holds greater promise for increasing the productivity of legumes and cereal crops. Here, an attempt is made in this chapter to highlight the role of PSM involving different microbial groups, used either alone or in combination, in the promotion of growth and yield of legumes and cereal crops in different production systems.
[Show abstract][Hide abstract] ABSTRACT: Plant growth promoting rhizobacteria affects the overall performance of plants by one or combination of mechanisms. However, little information is available on how ACC deaminase secreting bacteria enhance crop production. The present study aimed at identifying ACC deaminase producing and phosphate solubilizing bacterial strains and to assess their plant growth promoting activities. Additionally, the effect of two ACC deaminase positive bacterial strains Pseudomonas putida and Rhizobium leguminosarum on pea plants was determined to find a novel and compatible bacterial pairing for developing efficient inoculants for enhancing legume production and reducing dependence on chemical fertilizers. The isolated bacterial cultures were characterized biochemically and by 16S rRNA sequence analysis. The plant growth promoting activities was determined using standard microbiological methods. The impact of P. putida and R. leguminosarum, on pea plants was determined both in pots and in field environments. Of the total 40 bacterial strains, strain PSE3 isolated from Mentha arvenss rhizosphere and RP2 strain from pea nodules produced ACC deaminase, solubilized insoluble phosphate, synthesized indole acetic acid, ammonia, cyanogenic compounds, exopolysaccharides and had antifungal activity. The dual inoculation of P. putida strain PSE3 and R. leguminosarum strain RP2 had largest positive effect and markedly increased the growth, symbiotic characteristics, nutrient pool and quantity and quality of pea seeds. The measured parameters were further augmented when inoculated pea plants were grown in soils treated with urea or DAP. A significant variation in the measured parameters of pea plants was observed under both pot and field trials following microbial inoculation but the bacterial cultures did not differ significantly in growth promoting activities. The results suggest that ACC deaminase positive bacterial cultures endowed with multiple potential can be targeted to develop mixed inoculants for enhancing pea production and hence, to reduce dependence on synthetic fertilizers.
[Show abstract][Hide abstract] ABSTRACT: Pseudomonas aeruginosa strain OSG41, isolated from the heavy metal contaminated water irrigated to rhizospheric soil of mustard crop, tolerated chromium up to the concentration of 1800 μg ml−1 and reduced it by 100% at pH 6–8 after 120 h incubation at 30–40 °C. P. aeruginosa produced plant growth-promoting substances, both in the presence and absence of chromium; it produced 32 μg ml−1 indole acetic acid ml−1, in Luria Bertani broth with 100 mg tryptophan ml−1, solubilized tri-calcium phosphate (417 μg ml−1) and secreted 20.8 μg ml−1 exopolysaccharides (EPS) which decreased with increasing concentration of chromium added to growth medium. While investigating the impact of hexavalent chromium on chickpea, chromium application to soil had a phytotoxic effect. The application of P. aeruginosa strain OSG41 even with three times concentration of chromium increased the dry matter accumulation, symbiotic attributes (like nodule formation), grain yield and protein of chickpea compared to non-inoculated plants. The bio-inoculant decreased the uptake of chromium by 36, 38 and 40% in roots, shoots and grains, respectively. The present finding suggests that the bioinoculant effectively reduced the toxicity of hexavalent chromium to chickpea plants and concurrently enhanced the biological and chemical characteristics of chickpea, when grown in chromium treated soils.
European Journal of Soil Biology 05/2013; 56. DOI:10.1016/j.ejsobi.2013.02.002 · 2.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The study was navigated to examine the metal biosorbing ability of bacterial strain OSM29 recovered from rhizosphere of cauliflower grown in soil irrigated consistently with industrial effluents. The metal tolerant bacterial strain OSM29 was identified as Bacillus thuringiensis following 16S rRNA gene sequence analysis. In the presence of the varying concentrations (25-150 mgl(-1)) of heavy metals, such as cadmium, chromium, copper, lead and nickel, the B. thuringiensis strain OSM29 showed an obvious metal removing potential. The effect of certain physico-chemical factors such as pH, initial metal concentration, and contact time on biosorption was also assessed. The optimum pH for nickel and chromium removal was 7, while for cadmium, copper and lead, it was 6. The optimal contact time was 30 min. for each metal at 32 ± 2 °C by strain OSM29. The biosorption capacity of the strain OSM29 for the metallic ions was highest for Ni (94%) which was followed by Cu (91.8%), while the lowest sorption by bacterial biomass was recorded for Cd (87%) at 25 mgl(-1) initial metal ion concentration. The regression coefficients obtained for heavy metals from the Freundlich and Langmuir models were significant. The surface chemical functional groups of B. thuringiensis biomass identified by Fourier transform infrared (FTIR) were amino, carboxyl, hydroxyl, and carbonyl groups, which may be involved in the biosorption of heavy metals. The biosorption ability of B. thuringiensis OSM29 varied with metals and was pH and metal concentration dependent. The biosorption of each metal was fairly rapid which could be an advantage for large scale treatment of contaminated sites.
Saudi Journal of Biological Sciences 04/2013; 20(2):121-129. DOI:10.1016/j.sjbs.2012.11.006 · 0.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Biofabricated metal nanoparticles are generally biocompatible, inexpensive, and ecofriendly, therefore, are used preferably in industries, medical and material science research. Considering the importance of biofabricated materials, we isolated, characterized and identified a novel bacterial strain OS4 of Stenotrophomonas maltophilia (GenBank: JN247637.1). At neutral pH, this Gram negative bacterial strain significantly reduced hexavalent chromium, an important heavy metal contaminant found in the tannery effluents and minings. Subsequently, even at room temperature the supernatant of log phase grown culture of strain OS4 also reduced silver nitrate (AgNO3) to generate nanoparticles (AgNPs). These AgNPs were further characterized by UV-visible, Nanophox particle size analyzer, XRD, SEM and FTIR. As evident from the FTIR data, plausibly the protein components of supernatant caused the reduction of AgNO3. The cuboid and homogenous AgNPs showed a characteristic UV-visible peak at 428 nm with average size of ∼93 nm. The XRD spectra exhibited the characteristic Bragg peaks of 111, 200, 220 and 311 facets of the face centred cubic symmetry of nanoparticles suggesting that these nanoparticles were crystalline in nature. From the nanoparticle release kinetics data, the rapid release of AgNPs was correlated with the particle size and increasing surface area of the nanoparticles. A highly significant antimicrobial activity against medically important bacteria by the biofabricated AgNPs was also revealed as decline in growth of Staphylococcus aureus (91%), Escherichia coli (69%) and Serratia marcescens (66%) substantially. Additionally, different cytotoxic assays showed no toxicity of AgNPs to liver function, RBCs, splenocytes and HeLa cells, hence these particles were safe to use. Therefore, this novel bacterial strain OS4 is likely to provide broad spectrum benefits for curing chromium polluted sites, for biofabrication of AgNPs and ultimately in the nanoparticle based drug formulation for the treatment of infectious diseases.
PLoS ONE 03/2013; 8(3):e59140. DOI:10.1371/journal.pone.0059140 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Phosphorus (P) is one of the major plant nutrients whose deficiency results
in severe losses to crop yields. To achieve optimum crop production, P is,
therefore, consistently required. The use of chemical fertilizers in contrast
is discouraged for two basic reasons: one, the repeated and injudicious
application may alter soil fertility by adversely affecting microbial composition
and functions and, second, it is expensive. To address these problems, scientists
have identified soil-borne microorganisms belonging to a specific functional
group generally referred to as phosphate-solubilizing microorganisms (PSM)
which play many ecophysiological roles, especially in providing plants with
P. They can be found in any environment from conventional to contaminated
ones and are able to express their activity both in vitro and under field
conditions. The solubilization of P by bacteria including even some of the strict
nitrogen fixers, for example, rhizobia (symbiotic) or Azotobacter (asymbiotic),
is a multifactor process. The ability to release bound P from both organic
(enzymatic) and inorganic (acidification) sources by this functionally diverse
group of organisms and to provide growth regulators (phytohormones) to plants
or protecting plants from various diseases through other mechanisms (such as
synthesizing antibiotics, siderophores, cyanogenic compounds, etc.) is indeed
some of the most fascinating biological traits that have resulted in increased
crop yields. Here, we highlight the functional aspects of PS bacteria especially
their role in crop improvement particularly legumes and cereals grown in varied
agro-ecological regions. The discussion attempted here is likely to serve as
a low-cost prospective option for sustainable agriculture and also to solve
economic constraint to considerable extent faced by the farming communities.
01/2013: chapter Functional Aspect of Phosphate-Solubilizing Bacteria: Importance in Crop Production; Springer-Verlag Berlin Heidelberg.
[Show abstract][Hide abstract] ABSTRACT: Legume species of the flowering family Fabaceae are well known for their ability to fix atmospheric nitrogen and enhance nitrogen pool of soil, leading to increase in crop especially legumes both in conventional or derelict soils. The interaction between Rhizobia and legumes provides nutrients to plants, increases soil fertility, facilitates plant growth and restores deranged/damaged ecosystem. These characteristics together make legume extremely interesting crop for evaluating the effect of heavy metals. Environmental pollutants like heavy metals at lower concentrations are required for various metabolic activities of microbes including Rhizobia and legume crops. The excessive metal concentrations on the other hand cause undeniable damage to Rhizobia, legumes and their symbiosis. Currently, little is, however, known about how free-living Rhizobia or the legume–Rhizobium symbiosis is affected by varying metal concentration. We focus here that how the nitrogen-fixing root nodule bacteria, the “rhizobia,” increase plant growth and highlight gaps in existing knowledge to understand the mechanistic basis of how different metals affect rhizobia–legume symbiosis which is likely to help to manage legume cultivation in metal contaminated locations.
Toxicity of Heavy Metals to Legumes and Bioremediation, 01/2012: pages 29-44; , ISBN: 978-3-7091-0729-4
[Show abstract][Hide abstract] ABSTRACT: Globally, rapidly increasing industrialization and urbanization have resulted in the accumulation of higher concentrations of heavy metals in soils. The highly contaminated soil has therefore become unsuitable for cultivation probably because of the deleterious metal effects on the fertility of soils among various other soil characteristics. In addition, the uptake of heavy metals by agronomic crops and later on consumption of contaminated agri-foods have caused a serious threat to vulnerable human health. Considering these, a genuine attempt is made to address various aspects of metal contamination of soils. In addition, the nutritive value of some metals for bacteria and plants is briefly discussed. Here, we have also tried to understand how heavy metals risk to human health could be identified. These pertinent and highly demanding discussions are likely help to strategize the management options by policy makers/public for metal toxicity caused to various agro-ecosystems and for human health program.
Toxicity of Heavy Metals to Legumes and Bioremediation., 01/2012: chapter Soil Contamination, Nutritive Value and Human Health Risk Assessment of Heavy Metals: An Overview: pages 1-28;
Toxicity of Heavy Metals to Legumes and Bioremediation, 01/2012: chapter Heavy Metal Toxicity to Symbiotic Nitrogen-Fixing Microorganism and Host Legumes. In: Toxicity of Heavy Metals to Legumes: pages 29-44; Springer-Verlag/Wien.
[Show abstract][Hide abstract] ABSTRACT: Pollution of the environment by toxic metals in recent years has accelerated dramatically due to rapid industrial progress. Heavy metals when taken up in amounts in excess of the normal concentration produce lethal effects on plants, on microbes, and directly or indirectly on the human health. Deleterious impact of metals on plants includes the reduction in germinability of seeds, inactivation of enzymes, damage to cells by acting as antimetabolites, or formation of precipitates or chelates with essential metabolites. Heavy metals also show unconstructive effects on other physiological processes like photosynthesis, gaseous exchange, water relations, and mineral/nutrient absorption by plants. These adverse effects may be due to the generation of reactive oxygen species which may cause oxidative stress. The impact of heavy metals on germination of legume seeds and different physiological events of plants with special reference to leguminous plants grown in distinct agroecological niches is highlighted.
Toxicity of Heavy Metals to Legumes and Bioremediation, 01/2012: pages 45-66; , ISBN: 978-3-7091-0729-4
[Show abstract][Hide abstract] ABSTRACT: Heavy metal contamination resulting from rapid industrialization and other sources is a growing problem worldwide. Increasing pollution of soils with heavy metals disturbs the microbial biodiversity, soil fertility, and plant production and may cause significant human health problems. The excessive accumulation of heavy metals within plant tissues can modify protein structure or replace an essential element causing chlorosis, growth impairment, browning of roots, and photosystems dysfunction. To circumvent metal toxicity, bioremediation, a process that involves the use of biological materials to detoxify the contaminated sites and brings the environment to its contaminant free (original) state, has emerged as a promising alternative to widely practiced physicochemical methods used to clean up contaminated lands. Biological materials used to remediate contaminated sites are inexpensive, are easy to operate, do not produce hazardous by-products, and can be effective even if metals are present in low concentrations. Here, we integrate the knowledge obtained so far on the removal of metals and metalloids employing bioremediation strategies for contaminated soils. The information regarding different types of bioremediation and the challenges facing bioremediation are highlighted. The role and impacts of plant-growth-promoting rhizobacteria on bioremediation efficiency are addressed.
Toxicity of Heavy Metals to Legumes and Bioremediation, First Edition edited by Almas Zaidi, Parvaze Ahmad Wani, Mohammad Saghir Khan, 01/2012: chapter Bioremediation: A Natural Method for the Management of Polluted Environment: pages 101-114; SPRINGER-VERLAG., ISBN: 978-3-7091-0730-0
Biomanagement of Metal Contaminated Soil., 01/2011: chapter Importance of free living fungi in heavy metal remediation. In: Biomanagement of Metal Contaminated Soil.: pages 479-494; Springer The Netherlands.
[Show abstract][Hide abstract] ABSTRACT: The soil environment is a major sink for multitude of chemicals and heavy metals, which inevitably leads to environmental contamination problems. Indeed, a plethora of different types of heavy metals are used and emanated through various industrial activities. Millions of tonnes of trace elements are produced every year from the mines in demands for newer materials. On being discharged into soil, the heavy metals get accumulated and may disturb the soil ecosystem, plant productivity, and also pose threat to human health and environment. Therefore, the establishment of efficient and inexpensive methodology and techniques for identifying and limiting or preventing metal pollution, causing threats to the agricultural production systems and human health, is earnestly required. The possible genotoxic effects of heavy metals on plants and other organisms have been extensively investigated worldwide and sufficiently discussed in this chapter. Also, the development and applications of new biomonitoring methodologies for assessment of soil genotoxicity have been emphasized. The molecular techniques being employed either alone or in combination for detecting the DNA damage induced by heavy metal–contaminated soils and other potentially genotoxic compounds are adequately elaborated. Indeed, the combination of two techniques leads to the precise and efficient detection and quantification of the sublethal genotoxic effects induced in the plant bioindicators by contaminated soil. Thus, the application of biomonitoring protocols in conjunction with the genotoxic assessment of contaminated soil will be advantageous in effective management of heavy metal–polluted soils.
[Show abstract][Hide abstract] ABSTRACT: Discharge of heavy metals from various human activities including agricultural practices and metal processing industries is known to cause adverse effects on the environment. Even though conventional technologies adopted for removal of heavy metals from polluted environment tend to be efficient, they are generally expensive and produce huge quantity of toxic chemical products. The use of biological materials including fungal biomass offers an economical, effective, and safe option for removing heavy metals and, therefore, has emerged as a potential alternative method to conventional treatment techniques. Among the various remediation strategies, biosorption of heavy metals by metabolically active or inactive nonliving (dead) biomass of fungal origin is an innovative and alternative technology for removal of metals from contaminated sites. Due to unique chemical composition, fungal biomass sequesters metal ions by forming metal complexes with certain reactive groups on their cell surface and does not require growth-supporting conditions. Biomass of numerous fungi like Aspergillus, Penicillium, Mucor, Rhizopus, etc., has been found to have highest metal adsorption capacities. Biomass generated as a by-product of fermentative processes offers great potential for adopting an economical metal-recovery system. The purpose of this chapter is to gather state of the art information on the use of fungal biomass and explores the possibility of exploiting them for heavy metal remediation.
[Show abstract][Hide abstract] ABSTRACT: Soils contaminated with heavy metals present a major threat to nodule-forming rhizobia, legumes, and symbiosis formed by the
interacting symbionts. The symbiotic relation, as it occurs generally in economically important legumes, has deep impact on
human interest. However, in legume–Rhizobium symbiosis, maximum yield is possible only when there is suitable condition for both symbiotic partners. Thus, understanding
the effects of heavy metals on rhizobia–legume symbiosis will be useful. Although mechanical and chemical processes have been
used to clean up metal-contaminated soils, most traditional remediation technologies do not provide acceptable solutions for
the removal of metal from soils. The use of metal tolerant/detoxifying microbes offers a viable and inexpensive alternative
technology to clean up polluted soils. Metal-tolerant microbes not only help to remediate the contaminated soils, but also
provide elements essential to the growing legumes. Given the importance of legumes in animal and human consumption and their
role in maintaining soil fertility, attention is paid to understand how rhizobia develops resistance to various heavy metals.
Possible role of symbiotic nitrogen fixers in the metal-contaminated soils and how these microbes influence the productivity
of various legumes in metal-contaminated soils across different geographical regions are discussed.