Molecular mechanism of selenite reduction by Bacillus amyloliquefaciens BB61 based on transcriptome analysis

The microbial conversion of selenite represents an effective detoxification and assimilation process, although the underlying mechanisms remain incompletely understood. In this study, strain BB61 was a probiotic isolated from piglet feces and identified as Bacillus amyloliquefaciens, which could almost completely reduce 0.1 g/L Na₂SeO₃ to SeNPs within 48h. We investigated the potential mechanisms of selenite reduction in this strain through transcriptome sequencing and qPCR. The transcriptome analysis revealed the up-regulation of 829 genes and the down-regulation of 892 genes in response to 1 g/L Se treatment (padj <0.05) in Bacillus amyloliquefaciens BB61. GO (Gene Ontology) enrichment analysis indicated that DEGs (Differentially expressed genes) were predominantly associated with transmembrane transporters, ion transmembrane transport, cytoplasmic and cell membrane composition, cell movement and localization, and carbon metabolism. Additionally, the KEGG (Encyclopedia of Genes and Genomes) pathway annotation analysis revealed that the DEGs were primarily involved in the pentose phosphate pathway, pyruvate metabolism, pyrimidine metabolism, cofactor biosynthesis, and other pathways (P < 0.05). Among the highly expressed reductases, thioredoxin reductase (TrxA/B), nitrite reductase (NfsA), and selenite reductase (NamA) were all found to be up-regulated. Consequently, this study established a reduction pathway model for Se (IV), offering new insights into the molecular mechanisms underlying the bioreduction of selenite to form SeNPs.