Selenium (Se) exists in various chemical forms, including inorganic Se, organic Se, and Se nanoparticles (SeNPs). However, the mechanisms underlying the interaction between Se and gut microbiota remain unclear. This study systematically evaluated the effects of different polysaccharide‐stabilized Se nanoparticles (PS‐SeNPs) using an in vitro colonic fermentation model. The results indicate that the molecular properties of polysaccharides (PS) are key factors influencing the gut microbiota‐modulating effects of PS‐SeNPs. Specifically, high molecular weight and positively charged PS enhance the microbial utilization of SeNPs. Chitosan‐based Se nanoparticles (CS‐Se) and chitosan quaternary ammonium salt‐based Se nanoparticles (HACC‐Se) can specifically enrich beneficial bacterial communities, such as Lactobacillus and Bacteroidales , which possess both acid production and Se metabolism capabilities. This enrichment significantly promotes the accumulation of short‐chain fatty acids and the generation of selenocystine (SeCys ₂ ) and Se‐Methylselenocysteine (MeSeCys). Metabolomics analysis further showed significant activation of amino acid biosynthetic pathways. Chitosan oligosaccharide‐based Se nanoparticles (COS‐Se) and carboxymethyl cellulose‐based Se nanoparticles (CMC9‐Se) can enrich beneficial microorganisms. However, their bioavailability and microbial assimilation efficiency remain relatively limited. The H ₂ SeO ₃ group significantly promoted the proliferation of microorganisms such as Enterobacteriaceae, Escherichia‐Shigella, and Klebsiella . Our findings could improve understanding of the interaction between Se and gut microbiota.

In order to efficiently treat the biogas slurry through energy-conserving and carbon neutral biological process, consortiums were constructed by bacteria and microalgae isolated from biogas slurry that can tolerate high concentrations of pollutants. The biomass productivity, SOD, photosynthetic activity, nutrient removal and value-added products' production were monitored. The enhancement rate was introduced to quantify the interaction between bacteria and microalgae. Coculture of the obtained microalgae and bacteria could significantly improve the tolerance of symbiosis to pollutants, increase lipid and FAME production, promote nutrients removal, and reduce carbon emissions compared to monoculture. The coculture of Chlorella sp. GZQ001 and Lysinibacillus sp. SJX05 performed best, biomass productivity was 113.25 mg·L-1·d-1, nutrient removal efficiencies for NH4+-N, TN, TOC and TP were 83.17%, 82.07%, 34.03% and 76.60%, lipid, protein and FAME productions were 192.29, 409.51 and 36.48 mg·L-1. And it has been proved a symbiotic system with the potential to treat enhanced biogas slurry.