Table 2_Multiomics profiling of transcriptional and metabolic responses of Bacillus siamensis LSZ23 to corn straw.xls

Although Bacillus siamensis is valued for plant growth promotion and biocontrol, its lignocellulose-degrading capacity and regulation remain largely unexplored. B. siamensis LSZ23, isolated from humic soil in Inner Mongolia, China, produced a balanced cellulolytic system (CMCase 0.321, β-glucosidase 0.275, avicelase 0.240 and FPase 0.209 U/mL in 24 h LB culture) and reduced sterilised corn straw dry mass by 19.5% within 20 d in solid-state culture (10⁹ CFU/g), with scanning electron microscopy revealing extensive fibre-bundle disruption.

Its 4.12 Mb genome (46% GC, 4,120 protein-coding genes) encodes 570 predicted carbohydrate-active enzyme (CAZyme) genes, with marked expansion of glycoside hydrolase family GH1, and harbours 31 orthogroups absent from four reference genomes, notably oligosaccharide ATP-binding cassette transporters and starch-processing enzymes. Upon straw exposure, transcriptomics (173 differentially expressed genes) and metabolomics (1,094 differentially abundant metabolites) indicated coordinated reprogramming rather than simple enzyme amplification: motility and chemotaxis genes were repressed, the biofilm-matrix gene tapA was induced, carbon uptake shifted transcriptionally towards a phosphotransferase system-mediated cellobiose route, and the glutamine synthetase-glutamate synthase pathway and de novo purine biosynthesis were downregulated, consistent with reduced high-cost anabolism.