The nanomaterials synthesis is an intensifying research field due to their wide applications. The high surface-to-volume ratio of nanoparticles and quick interaction capacity with different particles make them as an attractive tool in different areas. Conventional physical and chemical procedures for development of metal nanoparticles become outmoded due to extensive production method, energy expenditure and generation of toxic by-products which causes significant risks to the human health and environment. Hence, there is a growing requirement to search substitute, non-expensive, reliable, biocompatible and environmental friendly methods for development of nanoparticles. The nanoparticles synthesis by microorganisms has gained significant interest due to their potential to synthesize nanoparticles in various sizes, shape and composition with different physico-chemical properties. Microbes can be widely applied for nanoparticles production due to easy handling and processing, requirement of low-cost medium such as agro-wastes, simple scaling up, economic viability with the ability of adsorbing and reducing metal ions into nanoparticles through metabolic processes. Biogenic synthesis of nanoparticles offers clean, non-toxic, environmentally benign and sustainable approach in which renewable materials can be used for metal reduction and nanoparticle stabilization. Nanomaterials synthesized through microbes can be used as a pollution abatement tool as they also contain multiple functional groups that can easily target pollutants for efficient bioremediation and promotes environmental cleanup. The objective of the present review is to highlight the significance of micro-organisms like bacteria, actinomycetes, filamentous fungi, yeast, algae and viruses for nanoparticles synthesis and advantages of microbial approaches for elimination of heavy metals, dyes and wastewater treatment.

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Evolutionary relationships of 120 root-nodulating bacteria isolated from the nodules of Pisum sativum cultivated at 22 different locations of the trans-Himalayan valleys of Lahaul and Spiti in the state of Himachal Pradesh of India were studied using 16S rRNA gene PCR-RFLP, ERIC-PCR, sequencing of 16S rRNA, atpD, recA, nodC and nifH genes, carbon-source utilization pattern (BIOLOG™), and whole-cell fatty acid profiling. The results demonstrated that all isolates belonged to Rhizobium leguminosarum symbiovar viciae (Rlv). Isolates from the two valleys were clearly separated on the basis of ERIC fingerprints, carbon-source utilization pattern, and whole-cell fatty acid methyl esters. Phylogenetic analysis of atpD, recA, nodC and nifH genes revealed a common Rlv sublineage in Spiti valley. Lahaul valley isolates were represented by three sequence types of atpD and recA genes, and four sequence types of nodC and nifH genes. Genotypes from the two valleys were completely distinct, except for two Lahaul isolates that shared nodC and nifH sequences with Spiti isolates but were otherwise more similar to other Lahaul isolates. Isolates from the two highest Spiti valley sites (above 4000 m) had a distinctive whole-cell fatty acid profile. Spiti valley isolates are closely related to Rlv sublineages from Xinjiang and Shanxi provinces in China, while Lahaul valley isolates resemble cosmopolitan strains of the western world. The high mountain pass between these valleys represents a boundary between two distinct microbial populations.

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