Halomonas Venusta Mediated Detoxification and Biotransformation of Selenite Into Selenium Nanoparticles Exhibiting Various Biomedical Applications

Abstract

Marine environment is in constant threat due to anthropogenic activities which are involved in disturbing the aquatic flora and fauna due to accumulation of toxic metals and metalloids. The current study involves the use of microbial remediation strategy for reduction of toxic sodium selenite (Na2SeO3) into less toxic elemental Se (Se0) with concurrent synthesis of Se nanoparticles (SeNPs) possessing several biomedical potential. Selenite reducing bacterial strain isolated from Mandovi estuary of Goa, India was identified as Halomonas venusta based on 16S rRNA gene sequence analysis and designated as strain GUSDM4. It's maximum tolerance level for Na2SeO3 was 100 mM. The 2, 3-diaminonaphthalene based spectroscopic analysis clearly demonstrated 93% reduction of 4 mM Na2SeO3 to Se0 during late stationary growth phase of Halomonas venusta. Biosynthesis of SeNPs commenced within 4 h during log phase which was clearly evident from red colour in the growth medium and a characteristic peak at 265 nm revealed by UV-Vis spectrophotometry. The intracellular synthesis of SeNPs was confirmed by transmission electron microscopy (TEM) of these bacterial cells. Characterization of SeNPs by X-ray crystallography, TEM and energy dispersive X-ray analysis clearly demonstrated spherical SeNPs of 20-80 nm diameter with hexagonal crystal lattice. These SeNPs at 50 µg/mL exhibited 90% free radical scavenging activity and also demonstrated anti-biofilm activity at 20 µg/mL against common human pathogens which was evident by SEM analysis. These SeNPs interestingly revealed excellent dose-dependent and selective anti-proliferative activity against A549 cancer cell line and mosquito larvicidal activity against Aedes aegypti, Culex quinquefasciatus and Anopheles stephensi. Therefore, these studies have demonstrated amazing potential of marine bacterium, Halomonas venusta in bioremediation along with biosynthesis of SeNPs and their applications as free radical scavenger, anti-biofilm, chemo-therapeutic and larvicidal agents which is the first report of its kind.