Bacterial biosynthesis of nanoparticle

Research has focused strongly on prokaryotes as a means of synthesizing metallic nanoparticles. Due to their great number in the environment and their ability to adapt to extreme conditions, bacteria considered as a great choice for study. Bacteria characterized as fast growing, inexpensive to cultivate and easy to manipulate. Growth conditions such as incubation period, temperature and oxygenation can be easily controlled (Pantidos and Horsfall, 2014). The changing the pH of the growth medium during incubation period leads to the production of nanoparticles of differing size and shape. Controlling such properties is important, due to varying sizes of nanoparticles are required for various applications such as optics, catalysts or antimicrobials (He et al.,2007).

Bacteria play a critical role in metal biogeochemical cycling and mineral formation in subsurface and surface environments (Southam and Saunders 2005). The use of microbial cells for the biosynthesis of nanosized materials has considered as a new approach for the synthesis of metal nanoparticles. Although the pains directed recently towards the biosynthesis of nanomaterials, the interactions between metal and microorganisms have been well documented and the ability of them to extract or/and accumulate metals is employed in commercial biotechnological processes as bioleaching and bioremediation (Gericke and Pinches, 2006). Bacteria have ability to produce inorganic materials either intracellularly or extracellularly. Microorganisms are considered as a potential bio-factory for the synthesis of nanoparticles such as gold, silver and cadmium sulfide.

Bacteria always synthesize inorganic materials, using extracellular or intracellular mechanisms. Microorganisms are considered as a possible biofactory for the synthesizing of nanoparticles as Au, Ag and CdS. Such as known bacteria Escherichia coli, Pseudomonas stutzeri, Pseudomonas aeruginosa, Plectonema boryanum, Salmonella typhi, Staphylococcus currens and Vibrio choleraehave attracted much attention for the biosynthesis of metallic nanoparticles through extracellular and intracellular mechanisms (Klaus et al., 1999). Moreover, some bacteria for the synthesis of inorganic nanoparticles have been recognized, as S-layer bacteria for producing gypsum and calcium carbonate layers and magnetotactic bacteria which are employed for magnetic nanoparticles (Shankar et al., 2004). A number of microorganisms have ability to live and grow at the high concentrations of metal ions, due to their resistance to the metal. The mechanisms involve: bioaccumulation, biosorption, efflux systems, solubility alteration and toxicity, the lack of particular metal transport systems and an extracellular complex at the precipitation of metals (Husseiny et al., 2007).