seminar on Fabrication of Biogenic Antimicrobial Silver Nanoparticles by Streptomyces aegyptia NEAE 102 as Eco-Friendly Nanofactory.

1. INTRODUCTION


Nanomaterials have a long list of applicability in improving human life and its environment. An important area of research in nanotechnology is the biosynthesis of nanoparticles such as nanosilver. The extremely small size and large surface area relative to their volume makes them useful for applications in various fields, such as antibacterials (Souza et al., 2004), therapeutics (Wang et al., 2011), high-sensitivity bio molecular detection and diagnostics, silver-nano coated medical devices (Tomsmic et al., 2009), optical receptors (Schult et al., 2000),  nonlinear optics, spectrally selective coating for solar energy absorption, bio-labelling, intercalation materials for electrical batteries, catalysis in chemical reactions. (Kowshik et al., 2003), cosmetics, microelectronics, and conductive inks and adhesives Silver nanoparticles (AgNPs) are currently commonly synthesized by chemical reduction 
(Peterson et al., 2007), thermal treatment (Sun et al., 2005), irradiation (Shao et al., 2006) and laser ablation (Tsuji et al., 2002) which are low yield, energy-intensive, difficult to scale up, often producing high levels of hazardous wastes, and may require the use of organic solvents and toxic reducing agents like sodium borohydride and N,N-dimethylformamide. Thus, these techniques yield extremely expensive materials. In addition, produced nanoparticles exhibit undesirable aggregation with time. Hence, a green synthesis method has been developed to obtain biocompatible, cost-effective, clean, nontoxic, easily scaled up for large-scale synthesis, and eco-friendly size-controlled nanoparticles. Microbial properties of bioaccumulation, biosorption, bio-detoxification, and bio-mineralization have been regarded as opportunities to use them as nano factories for mining nano materials (Narayanan et al., One of the major issues to be considered during synthesis of nanoparticles is their size, depending on which the applications may vary (Gurunathan et al., 2009). Biosynthetic methods can be categorized into intracellular and extracellular synthesis according to the place where nanoparticles are formed (Tang et al., 2011). For extracellular synthesis, it is reported that a reductase enzyme is released into solution, which reduces a salt to its metallic solid nanoparticles through the catalytic effect (Souza et al., 2004). Extracellular secretion of enzymes offers the advantage of obtaining large quantities in a relatively pure state, free from other cellular proteins associated with the organism, and can be easily processed by filtering of the cells and isolating the enzyme for nanoparticles synthesis from cell free filtrate.                                                                     

Fabrication of Biogenic Antimicrobial Silver Nanoparticles by Streptomyces aegyptia NEAE 102 as Eco-Friendly Nanofactory Various microorganisms (bacteria, yeast, fungi) are known to synthesize silver nanoparticles. The produced nanoparticles have different sizes and shapes.The shape of AgNPs, predominantly spherical, is common to microbial-mediated synthesis (Shivaji et al., 2011). Nanoparticles resulting from some microbial processes are composite materials and consist of an inorganic component and a special organic matrix (proteins, lipids, or polysaccharides) and they have unique chemical and physical properties different from the properties of conventionally produced nanoparticles and of other microorganisms even when they are incubated in the same medium under the same conditions (Nelly et al., Traditionally, fermentation processes have been optimized by changing one independent variable or factor at a time while keeping the others at some fixed values. The disadvantages of such a classical method are that it is time consuming, laborious, and expensive; in addition, it ignores the combined interactions among different variables employed (Gao et al., 2009). Consequently, statistical methods are increasingly preferred for fermentation optimization because they reduce the total number of experiments needed and provide a better understanding of the interactions among factors on the outcome of the fermentation (Revankar et al., 2006). Response surface methodology (RSM) is a statistical technique based on the fundamental principles of statistics, randomization, replication, and duplication, which simplifies the optimization by studying the mutual interactions among the variables over a range of values in a statistically valid manner. It is an efficient statistical technique for optimization of multiple variables in order to predict the best performance conditions with a minimum number of experiments and explain the individual and interactive effects of test variables on the response (Panwal et al., 2011).

In this study, for the first time, a novel actinomycete strain, S. aegyptia NEAE 102, is utilized for the synthesis of silver nanoparticles. A statistical approach (central composite design) has been employed in the present study to optimize the extracellular biosynthesis of silver nanoparticles by the novel S. aegyptia NEAE 102. The biosynthesized nanoparticles were characterized for their surface properties using FTIR, in addition to antimicrobial properties using gram-positive, and gram-negative bacterial strains and yeast.


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