Bioconversion of selenite to selenium nanoparticles by <i>Paenibacillus polymyxa</i> P10: metabolic basis and potential for wastewater treatment

P10, isolated from estuarine sediment, as a highly tolerant and efficient Se(IV)-reducing bacterium. Strain P10 completely reduced 5 mM Se(IV) to Se nanoparticles (SeNPs) within 48 h and retained measurable Se(IV)-reducing activity up to 1,000 mM Se(IV). It also maintained activity over a wide range of pH (5-10), temperature (20-45°C), and salinity (1%-3.5%) conditions. In addition, P10 maintained high Se(IV) reduction performance over five repeated-batch cycles. Transcriptomic and enzymatic analyses showed that Se(IV) exposure triggered coordinated metabolic responses, including carbohydrate metabolism, oxidative phosphorylation, and nitrogen metabolism, which together supported energy generation and reductive transformation. Nitrite reductase-associated activity was linked to Se(IV) reduction. These findings establish strain P10 as a robust biocatalyst for Se(IV) detoxification and SeNP recovery, and provide mechanistic insight into microbial selenite reduction relevant to the development of scalable Se-containing wastewater treatment processes.IMPORTANCESelenite [Se(IV)] is among the most problematic selenium (Se) species in wastewater due to its high toxicity and mobility. Although microbial Se(IV) reduction is an attractive strategy for Se detoxification and recovery, its practical use is limited by the poor tolerance and weak environmental robustness of most known microorganisms. This study identifies a highly tolerant Se(IV)-reducing bacterium with broad adaptability to pH, temperature, and salinity stress, extending the known ecological and functional potential of microbial Se reducers. These findings strengthen the basis for developing more reliable bioprocesses for Se-contaminated wastewater treatment and Se resource recovery.