Biosynthesis of Selenium Nanoparticles by a Heavy Metal-Resistant Bacterium Stenotrophomonas sp. EGS12

Production of selenium nanoparticles (SeNPs) by chemical approaches is costly and environmentally hazardous, whereas biological methods, especially those using bacteria, can avoid these disadvantages. In this study, rapid biogenic synthesis of SeNPs by a heavy metal-resistant bacterium Stenotrophomonas sp., strain EGS12 was investigated. SeNPs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). TEM and SEM analysis showed that the SeNPs were spherical and ranged from 100 to 200 nm in size. EDX demonstrated that the SeNPs contained C, Se, O, P, and S, and the content of Se was 32.64%. The mechanism of SeNPs biogenic synthesis by this strain was also investigated. The results documented that the biogenic synthesis of SeNPs, consisting of reduction of selenite to elemental selenium, was conducted synergistically by two reductases: nitrite reductase and thiol-mediated reductase. Thus, a novel pathway of efficient SeNP biosynthesis by a heavy metal-resistant Stenotrophomonas genus strain was identified.