Bacteria: A Prospective Source of Metallic Nanoparticles
Research & Reviews: Research Journal of Biology
The rapid expansion of nanotechnology opens up new opportunities in antimicrobial research. According to the reports, biogenic metal and metal oxide nanoparticles represent a group of materials which investigated in respect to their antimicrobial effects. The antimicrobial activity of metals such as silver (Ag), copper (Cu), gold (Au), titanium (Ti), platinum (pt) and zinc (Zn), each having various properties, potencies and spectra of activity, has been known and functional for centuries. The
... or centuries. The emergence of resistance of pathogens towards antibiotics has been caused serious health problems. From this background, the metal based nanoparticles with excellent antibacterial activity have been the most broadly explored and are presently being used in a number of commercial products. In this study, we focused on the recent research works on the topic of antimicrobial activity of metal and metal oxide nanoparticles collectively with their synthesis from bacteria. Bacteria are favorite for the study due to their abundance in the surroundings and their capability to become accustomed to extreme conditions, to reproduce fast, inexpensive to cultivate and easy to control. Growth conditions such as temperature, oxygenation and incubation time can be easily controlled. During study changing the pH of the growth medium during incubation results in the production of nanoparticles of differing size and shape, He et al., reveals that  it is important to control such properties, because varying sizes of nanoparticles are necessary for diverse applications such as optics, catalysts or antimicrobials. Johnston et al., elaborates that pure gold nanoparticles can be manufactured by the bacterium Delftia acidovorans . The delftibactin production was associated with the help of resistance mechanism of D. acidovorans to toxic gold ions. By producing inert gold nanoparticles bound to delftibactin, the gold did not pose any toxicity for exposed cells. The mechanism responsible for the formation of metallic nanoparticles and how it can vary in different bacteria first reported by The Johnston group. Alternative methods had also been suggested by another group for gold nanoparticle synthesis by bacteria. He et al.,  experientially observed the extracellular formation of gold nanoparticles of 10-20 nm by the bacterium Rhodopseudomonas capsulate. These nanoparticles were synthesized via an NADH-Dependant Reductase suggested by the said group [1,3]. Palladium (Pd) is a metal that currently being primarily used as catalysts for dehalogenation and hydrogenation reactions, is member of the Platinum Group Metals (PGM) which posses a collection of highly catalytically active metals . Palladium (Pd), zero valent nanoparticles can be synthesised by means of bacteria found at Alpine sites heavily contaminated with heavy metals . Pseudomonas cells were involved in boosting catalytically active nanoparticles which were effectively used in reductive deha-logenation of tri and tetra-chlorinated dioxin congeners, among all the variety of heavy metal resistant bacteria, they have found in that environment, they found that . Escherichia coli, is also able to synthesize Pd nanoparticles with the help of hydrogenases found in the bacterium . In both studies, the Pd nanoparticles were establishing the cell envelope of the bacteria which makes them attractive because they are easily accessible. Bacillus licheniformis can produce intracellular AgNPs . After addition of silver ions, the colour of the culture turned a dark brown represents the presence of AgNPs . The nanoparticles were indeed made of Ag and also that they were quite dispersed in solution according to Kalimuthu and group. Pugazhenthiran et al. observed that intracellular AgNPs were produced when members of the Bacillus sp. were sub-cultured into media containing AgNO. The reaction need incubation time for 7 days, hence it is slow  .