Investigation of a hot-spring extremophilic Ureibacillus thermosphaericus strain thermo-BF for extracellular biosynthesis of functionalized gold nanoparticles

A systematic optimization process for simple and eco-friendly extracellular biosynthesis of gold nanoparticles by a native thermophilic Ureibacillus thermosphaericus strain thermo-BF isolated from geothermal hot springs has been presented. Biosynthesis reactions were conducted using the culture supernatant at different temperatures (60–80 °C) and pH (6–9) with gold ion concentration ranging from 0.001 to 0.1 M. The results obtained showed that pure spherical nanoparticles in the range of 35–75 nm were produced, and the maximum nanoparticle production was achieved using 0.001 M HAuCl₄ at 80 °C, pH 9. Genome mining and profiling of the genes encoding bioreducing enzymes in U. hermosphaericus strain thermo-BF revealed evidences indicating sulfur reduction capability of this bacterium. Overall, the findings of this study confirmed the great biocatalyzing potential of the extermophilic U. thermosphaericus strain thermo-BF supernatant for intensified biosynthesis of gold nanoparticle under extreme conditions.