Efficient Microbial Production of Selenium Nanoparticles by Selenium-Tolerant Alcaligenes sp. HZ-9-3-3.

Selenium (Se) is a crucial trace element for human and animal health, contributing significantly in various physiological processes. However, its uneven global distribution leads to widespread deficiencies. Nano-selenium (selenium nanoparticles, SeNPs), with low toxicity and high bioavailability, emerges as a promising alternative, and microbial synthesis is the preferred method for its production. In this study, we collected samples from the selenium-rich region of Enshi, Hubei Province, China, and used sodium selenite (NaSeO) gradient screening to isolate microorganisms capable of tolerating high selenium concentrations and efficiently producing SeNPs. We identified nine selenium-tolerant strains that withstand over 0.115 M of sodium selenite. Among these, strain HZ-9-3-3, identified as Alcaligenes sp., tolerated up to 0.231 M and effectively converted selenite to elemental selenium. Optimization using single-factor experiments and central composite design (CCD) established optimal conditions: inoculum size of 12.7% (±0.1%), pH 7, temperature 28 °C, and sodium selenite concentration of 0.0289 M, achieving a conversion rate of 69.7% (±0.1%). The produced SeNPs exhibited moderate antioxidant activity, with IC values of 1.5 mg/mL for DPPH radicals and 1.7 mg/mL for hydroxyl radicals, and a reducing power equivalent to 0.842 mg/mL of vitamin C. These findings highlight the potential of strain HZ-9-3-3 for efficient bioconversion of selenium and production of SeNPs with significant antioxidant properties.