Green Synthesis of Antibacterial Silver Nanoparticles using Yeast Isolates and its Characterization

The present study had investigated the role of yeasts, isolated from soil and food samples for its ability to synthesize silver nanoparticles. Serial dilution method followed by spread plate technique was used for isolation of yeasts on YEPD agar medium and the morphological characterization was done by simple staining technique. Primary screening was done by visual colour change followed by UV spectrophotometric analysis. Significant color change and prominent peaks around 420-450 nm were noted through UV spectrophotometric analysis in the cell free extract of Isolate 5, Isolate 8 and Isolate 13, revealed the synthesis of Ag-NPs. Optimization of growth parameters for the enhancement of Ag-NPs production was evaluated for each of the potent yeast isolates. Isolate 5 and 13 had showed highest Ag-NPs production after 24 h of incubation period, supplemented by fructose in the production medium of pH 9 along with 5mM substrate concentration of AgNO₃, at 45˚C, whereas in case of isolate 8, highest production was observed with 3mM concentration of Ag NO₃ at pH 8. FTIR analysis revealed the presence of significant peaks around 3441-3255, 2922-2964, 1576-1579, 1384-1415, 1276, 1153 and 1076cm^-1 of Ag-NPs synthesized by isolate 5,8 and 13 respectively, were corresponding to the functional groups produced during the synthesis of Ag-NPs. XRD results showed peaks at 2 theta values 27.29°, 31.76°, 45.91°, 54.26-56.77° and 75.56-75.99°, were corresponding to (111), (200), (222), (311), and (331) lattice of silver nanoparticles. Distinct surface topology of the AgNPs synthesised by the potent yeast isolates were observed by AFM analysis. Positive anti-oxidant and anti-bacterial activity were elucidated by AgNPs synthesised by the potent yeast isolates, wherein AgNPs were found to be bacteriostatic at low concentration (5ug/ml) and bactericidal at high concentrations (100ug/ml).