Characterization, antioxidant properties and transcriptome analysis of selenium nanoparticles biosynthesized by the high selenite tolerance strain Halomonas sp. SF2000

Microbial synthesis of selenium nanoparticles (SeNPs) has garnered significant attention in recent years due to its eco-friendly and sustainable nature. Numerous microorganisms possess the capability to reduce ionic selenium into SeNPs, a process often associated with microbial detoxification mechanisms. In this study, a strain exhibiting exceptionally high selenite tolerance (up to 1200 mM) was isolated from selenium-enriched organic fertilizers, representing the highest tolerance level reported to date. The strain was identified as Halomonas sp. SF2000. Furthermore, the selenite reduction capability of SF2000 was systematically investigated. The strain reduced 10 mM selenite completely within 60 h. Electron microscopy revealed that the synthesized SeNPs were spherical and predominantly localized extracellularly. Characterization showed that the nanoparticles had a zeta potential of −47.8 mV, confirming the stability of the system. Fourier transform infrared (FTIR) spectroscopy analysis provided insights into the surface functional groups of the nanoparticles. Additionally, the SeNPs exhibited significant antimicrobial activity, free radical scavenging ability, and antioxidant capacity, confirmed by in vitro assays. Transcriptomic analysis revealed that low selenite concentrations primarily upregulated genes associated with reduction activity, while high concentrations also induced the expression of resistance-related genes. This dual regulatory mechanism underpins the exceptional selenite tolerance of SF2000. Notably, this study provides the first report on selenite reduction capability by Halomonas sp., establishing a theoretical foundation for the potential application of SF2000 in environmental remediation, advanced materials, and functional health products.