BIOSYNTHESIS OF GOLD NANOPARTICLES BY BACTERIA FROM HYPERALKALINE SPRING AND EVALUATION OF THEIR INHIBITORY ACTIVITY AGAINST PYOCYANIN PRODUCTION

Nanoparticles are used in wide range of applications given their unique optical, chemical and electronic properties. Microbial biosynthesis of nanoparticles has offered a milder and eco-friendly alternative to physical and chemical methods of synthesis. One potential use of nanoparticles is for the inhibition of quorum sensing-mediated processes by microorganisms during pathogenic colonization and infection. In this study, bacteria from hyperalkaline spring (pH 11) were isolated using various enrichment media. The isolates, phylogenetically related to Lysinibacillus sp. and Pseudomonas stutzeri, were investigated for their ability to biosynthesize gold nanoparticles (AuNPs) via reduction of chloroauric acid (HAuCl4) at pH 9. Extracellular synthesis of gold nanoparticles was confirmed by UV-Vis absorption analysis which showed a peak at 500-600 nm wavelength range corresponding to the surface plasmon resonance of AuNPs. The AuNPs synthesized were of spherical and irregular shapes as revealed by SEM analysis. The presence of elemental gold was further confirmed by EDX analysis. FTIR results showed that various functional groups are possibly involved in the reduction of HAuCl4 and stabilization of synthesized gold nanoparticles. The inhibitory effect of biosynthesized AuNPs was tested on the growth and pyocyanin production of Pseudomonas aeruginosa PA01 during a 72-hour incubation period. Although the biosynthesized AuNPs showed no toxicity to the test organism, an increasing inhibition level of pyocyanin production was observed with increasing volumes of nanoparticles used. The levels of pyocyanin in setups treated with biosynthesized gold nanoparticles at 10, 30 and 50 L were significantly lower compared to the untreated setups (P ≤ 0.05). Our findings demonstrate that bacteria adapted to alkaline conditions can be used for efficient biosynthesis of AuNPs, which exhibited potential biomedical application in inhibiting pyocyanin production.