EPS-mediated biosynthesis of nanoparticles by Bacillus stratosphericus A07, their characterization and potential application in azo dye degradation.

Microbial exopolysaccharides (EPS) are biocompatible, biodegradable, and less toxic substances secreted outside the cell. They adsorb metal cations to its surface, making it another captivating property, which helps in stabilizing and biosynthesizing metal nanoparticles. Owing to these properties, we adopted bacterial EPS toward the green synthesis of nanoparticles and its application in the removal of azo dyes. Extracted EPS weighed 2.6 mg/mL from the most potential isolate A07 with 385 μg/mg of the carbohydrate content. The top three isolates were subjected to nanoparticle synthesis via the intracellular method and, by their extracted EPS, silver nanoparticles (AgNP) with the size around 87 nm were successfully produced by both methods mediated by the most potent isolate. The nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction studies, atomic force microscopy, and FT-IR analysis. The nanoparticles were employed for dye degradation of azo dyes, namely, Methyl Orange (MO) and Congo Red (CO). EPS-Ag NPs showed fair degradation capability determined by UV-Vis kinetic studies. The work suggests electron transfer from reducing agent to dye molecule mediated by nanoparticles, destroying the dye chromophore. This makes EPS-Ag NPs a suitable, cheap, and environment-friendly candidate for biodegradation of harmful azo dyes. The most potential isolate was identified as Bacillus stratosphericus by 16S rRNA sequencing and submitted to GenBank under the accession id MK968439.