Mohammad Oves

Size-dependent antimicrobial properties of CuO nanoparticles against Gram-positive and -negative bacterial strains

Background CuO is one of the most important transition metal oxides due to its captivating properties. It is used in various technological applications such as high critical temperature superconductors, gas sensors, in photoconductive applications, and so on. Recently, it has been used as an antimicrobial agent against various bacterial species. Here we synthesized different sized CuO nanoparticles and explored the size-dependent antibacterial activity of each CuO nanoparticles preparation. Methods CuO nanoparticles were synthesized using a gel combustion method. In this approach, cupric nitrate trihydrate and citric acid were dissolved in distilled water with a molar ratio of 1:1. The resulting solution was stirred at 100°C, until gel was formed. The gel was allowed to burn at 200°C to obtain amorphous powder, which was further annealed at different temperatures to obtain different size CuO nanoparticles. We then tested the antibacterial properties using well diffusion, minimum inhibitory concentration, and minimum bactericidal concentration methods. Results XRD spectra confirmed the formation of single phase CuO nanoparticles. Crystallite size was found to increase with an increase in annealing temperature due to atomic diffusion. A minimum crystallite size of 20 nm was observed in the case of CuO nanoparticles annealed at 400°C. Transmission electron microscopy results corroborate well with XRD results. All CuO nanoparticles exhibited inhibitory effects against both Gram-positive and -negative bacteria. The size of the particles was correlated with its antibacterial activity. Conclusion The antibacterial activity of CuO nanoparticles was found to be size-dependent. In addition, the highly stable minimum-sized monodispersed copper oxide nanoparticles synthesized during this study demonstrated a significant increase in antibacterial activities against both Gram-positive and -negative bacterial strains.

Plant growth promotion by phosphate solubilizing fungi – current perspective

Phosphorus is abundant in soils in both organic and inorganic forms; nevertheless, it is unavailable to plants. Accordingly, soil becomes phosphorus (P)-deficient, making P one of the most important nutrient elements limiting crop productivity. To circumvent the P deficiency, phosphate-solubilizing microorganisms could play an important role in making P available for plants by dissolving insoluble P. The dissolution of inorganic P by microbial communities including fungi is though common under in vitro conditions; the performance of phosphate-solubilizing microbes in situ has been contradictory. Fungi exhibit traits such as mineral solubilization, biological control, and production of secondary metabolites. As such, their potential to enhance plant growth when present in association with the roots is clear. The challenge is how to make use of such biological resources to maintain soil health while increasing the crop productivity by providing P to plants through the application of phosphate-solubilizing fungi. The present review focuses on the mechanisms of phosphate solubilization, development and mode of fungal inoculants application and mechanisms of growth promotion by phosphate-solubilizing fungi for crop productivity under a wide range of agro-ecosystems, and the understanding and management of P nutrition of plants through the application of phosphate-solubilizing fungi will be addressed and discussed.

Biosorption of heavy metals by Bacillus thuringiensis strain OSM29 originating from industrial effluent contaminated north Indian soil

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 (25-150xa0mgl(-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 30xa0min. for each metal at 32xa0±xa02xa0°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 25xa0mgl(-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.

Antibacterial and Cytotoxic Efficacy of Extracellular Silver Nanoparticles Biofabricated from Chromium Reducing Novel OS4 Strain of Stenotrophomonas maltophilia

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.

Soil Contamination, Nutritive Value, and Human Health Risk Assessment of Heavy Metals: An Overview

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.

Functional Diversity Among Plant Growth-Promoting Rhizobacteria: Current Status

Root-colonizing bacteria (rhizobacteria) that exert beneficial effects on plant development via direct or indirect mechanisms have been defined as plant growth-promoting rhizobacteria (PGPR). These natural bioresources provide essential nutrients to plants and improve growth, competitiveness, and responses to external stress factors by an array of mechanisms under different agro-ecosystems. The PGPR facilitate plant growth by synthesizing or altering: the concentration of phytohormones: asymbiotic and symbiotic N2 fixation, antagonism against phytopathogenic microorganisms by producing siderophores, antibiotics and cyanide; solubilization of mineral phosphates and other nutrients; and by synthesizing 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which helps to reduce the inhibitory effects of ethylene on plants. And hence, use of such PGPR may be a viable alternative to chemical fertilizers for increasing the productivity of various crops. However, despite their proven ability of growth promotion, PGPR have yet to fulfil their promise and potential as commercial bioinoculants. Understanding functional diversity of PGPR is vital for low-input sustainable production. Recent progress focusing on the principles and mechanisms of action of PGPR is reviewed and discussed.

Heavy Metal Toxicity to Symbiotic Nitrogen-Fixing Microorganism and Host Legumes

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.

Functional Aspect of Phosphate-Solubilizing Bacteria: Importance in Crop Production

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.

Role of Phosphate-Solubilizing Bacteria in Legume Improvement

Heterogeneously distributed microbial communities belonging to different genera enhance the growth and development of many crop plants including legumes. Among the various microbial populations inhabiting different habitats, the heterotrophic organisms endowed with natural phosphate-solubilizing activity and quite often called as phosphate-solubilizing microorganisms (PSM) supply one of the major plant nutrients, phosphorus, to plants and facilitate the growth of legumes. Phosphate-solubilizing microorganisms convert the complex or locked insoluble phosphorus to soluble phosphates by various mechanisms such as acidification, chelation, exchange reactions and polymeric substances formation and make it available to plants. Apart from supplying P to legumes, PSM also promote the growth of legumes by other mechanisms. Therefore, the widespread use of PSM in legume production helps both to reduce the spiralling cost of phosphatic fertilizers and to make soil free from chemical hazards. Considering these, the application of PSM endowed with multiple growth-promoting activities holds greater promise for increasing the productivity of legumes. Symbiotic/associative nitrogen-fixing bacteria are yet another important group of beneficial microbiota which is known to supply exclusively nitrogen to legumes, but they can also promote legume growth by other direct or indirect mechanisms. The co-inoculation of functionally different microflora such as N2-fixers, phosphate solubilizers and mycorrhizal fungi has, however, been found more effective than single inoculation of either organism for legume plants under nutrient-deficient soils. Basic and advance aspect of phosphate solubilization, mechanism of plant growth promotion and impact of single or synergistic association of phosphate solubilizers with other beneficial microflora on legumes growing in different regions are reviewed and discussed. The literatures surveyed in this chapter are likely to help better understand the functional role of PSM in sustainable production of legumes while reducing dependence on use of phosphatic fertilizers in legume production systems.

Factors Affecting the Variation of Microbial Communities in Different Agro-Ecosystems

Soil microbial communities play an important role in supplying essential nutrients to plants by decomposing various organic matters. Composition, structure and functions of microbial communities in soil are, however, under the constant control of the environment including various agricultural management practices. Due to scarcity of convenient methods for exploration, our understanding of the different degrees and dynamics of microbial community variations are limited. An attempt will be made to understand such structural and functional variations employing molecular tools. Earlier it was believed that it is the plant community that exerts control over the microbial community, but recently, some findings have suggested that it is actually the microbial community that acts as a driver of plant community structure and dynamics. Attention will therefore be paid to highlight some of these issues, and the effect of various farm management practices on the composition and functions of microbial communities This is likely to lead to the development of best management practices for improving soil fertility and, consequently, agricultural productivity to improve the sustainability of agro-ecosystems.