Weiming Li

Sustainable bioprocesses for selenite [Se(IV)] remediation and selenium (Se) recovery are constrained by the limited tolerance of most reported microorganisms for elevated Se(IV) concentrations. Here, we identified Paenibacillus polymyxa 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. IMPORTANCE: Selenite [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.

Marine microalgae, as the primary producers in ocean ecosystems, play a critical role in global carbon cycling and are efficient accumulators of arsenic (As) from seawater, raising concerns about its trophic transfer through marine food webs. Rising terrestrial nutrient inputs, particularly excess nitrogen, have elevated nitrogen-to-phosphorus (N/P) ratios, representing a widespread ecological concern that alters marine biogeochemical cycles and threatens the survival of marine microalgae. A deeper understanding of how arsenic uptake and transformation biogeochemistry in marine microalgae respond to intensifying N/P ratios is thus crucial to predict the response of marine ecosystems and their contribution to global climate change. Despite these concurrent trends, the impact of altered nutrient dynamics on the arsenic biogeochemistry in marine microalgae remains largely unexplored. Here, we show that appropriately increased N/P ratios markedly enhance arsenic accumulation and promote the intracellular conversion of inorganic As to organic species. Transcriptome data further demonstrate that marine microalgae could significantly upregulate gene expressions associated with arsenic transport-related genes to cope with increased N/P ratios. Metabolomic flux analysis revealed that elevated N/P ratios promoted photosynthetic carbon fixation, ATP synthesis, and carbohydrate metabolism, while the amino acid metabolism was suppressed in marine microalgae, and the redirected energy flow may facilitate arsenic metabolism. Collectively, the reallocation of metabolic energy under high N/P conditions contributed to increased arsenic uptake and biotransformation in marine microalgae. An analysis of the Tara Oceans database confirmed these patterns and showed that arsenic metabolism-related genes are widely distributed across global surface oceans. Continuous nitrogen inputs and rising N/P ratios may alter arsenic speciation and mobility, benefiting cellular detoxification in the short term but potentially increasing organic arsenic accumulation, trophic transfer, and associated ecological and human health risks over longer time scales.

The BM composite, with biochar as a long-range electron-conducting scaffold and immobilized methyl viologen as a redox mediator, transfers electrons from Cac to Clj , driving the latter to assimilate CO ₂ released by the former.