A review on the biosynthesis of metal and metal salt nanoparticles by microbes

Abstract

Metal nanoparticles have received great attention from researchers across the world because of a plethora of applications in agriculture and the biomedical field as antioxidants and antimicrobial compounds. Over the past few years, green nanotechnology has emerged as a significant approach for the synthesis and fabrication of metal nanoparticles. This green route employs various reducing and stabilizing agents from biological resources for the synthesis of nanoparticles. The present article aims to review the progress made in recent years on nanoparticle biosynthesis by microbes. These microbial resources include bacteria, fungi, yeast, algae and viruses. This review mainly focuses on the biosynthesis of the most commonly studied metal and metal salt nanoparticles such as silver, gold, platinum, palladium, copper, cadmium, titanium oxide, zinc oxide and cadmium sulphide. These nanoparticles can be used in pharmaceutical products as antimicrobial and anti-biofilm agents, targeted delivery of anticancer drugs, water electrolysis, waste water treatment, biosensors, biocatalysis, crop protection against pathogens, degradation of dyes etc. This review will discuss in detail various microbial modes of nanoparticles synthesis and the mechanism of their synthesis by various bioreducing agents such as enzymes, peptides, proteins, electron shuttle quinones and exopolysaccharides. A thorough understanding of the molecular mechanism of biosynthesis is the need of the hour to develop a technology for large scale production of bio-mediated nanoparticles. The present review also discusses the advantages of various microbial approaches in nanoparticles synthesis and lacuna involved in such processes. This review also highlights the recent milestones achieved on large scale production and future perspectives of nanoparticles.

Fig. 1. A mechanistic scheme with graphical representation about the synthesis of metal nanoparticles from microbes [this figure has been adapted from ref. 163 with permission from Royal Society of Chemistry].

Fig. 2. Proposed mechanistic scheme of the bioreduction and stabilization of nanoscale particles by nitrate reductase enzyme.

Fig. 3. Synthesis of silver nanoparticles (AgNPs) by electron transfer in peptides. Scheme (1) Inhibited synthesis of AgNPs by photoinduced electron transfer in tetrapeptide 1/Ag⁺ solution. Scheme (2) AgNPs synthesis in tetrapeptide 2A–E/Ag⁺ solution by photoinduced electron transfer [this figure has been adapted from ref. 122 with permission from Wiley].

Fig. 4. (A) The proposed Metal-reducing (Mtr) extracellular electron transfer pathway of S. oneidensis MR-1 which is similar to bacterial metal nanoparticles synthesis outside the bacterial cell surface. CymA, MtrA, MtrC and OmcA are multiheme c-type cytochromes, while MtrB is a porin-like trans-outer membrane protein [this figure has been adapted from ref. 124 with permission from Frontiers]; (B) proposed mechanistic scheme of the biomineralization of gold ions by pullulan exopolysaccharide [this figure has been adapted from ref. 135 with permission from Elsevier].

Fig. 5. (A) Continuous reduction of toxic tellurite (Te^IV) oxyanions into recoverable tellurium nanoparticles using anaerobic sludge reactor [this figure has been adapted from ref. 153 with permission from Elsevier]; (B) parameters for producing monodispersed, stable, and high-yield biological nanoparticles [this figure has been adapted from ref. 16 with permission from Elsevier].