The effect of nitrogen availability and forms on the degradation pathway of lignocellulose by Bacillus subtilis

Nitrogen availability and forms significantly influence the efficiency of microbial lignocellulose degradation. Using Bacillus subtilis LP-10, a strain with strong lignocellulose-degrading capacity, as a model, we evaluated the effects of three concentration gradients inorganic nitrogen sources (NaNO₃, NH₄Cl, NH₄NO₃) on lignocellulose degradation pathway. By conducting a 30-day microcosm experiment simulating the decomposition of Larch needle litter and measured litter mass-loss rate, the activities of cellulolytic and ligninolytic enzymes, and the residual lignocellulose components. Under low nitrogen conditions (N1), transcriptome sequencing was performed for all three nitrogen sources and the control to identify differentially expressed CAZyme genes; Key targets were validated by RT-qPCR. The results indicate that low nitrogen concentrations promote lignocellulose degradation, whereas higher concentrations exert the opposite effect. NH₄Cl-N1 was most effective, yielding the highest mass-loss rate (9.823%), significant increases in six key lignocellulose-degrading enzymes, and the greatest reductions in residual lignocellulose. Transcriptomics showed that NH₄Cl triggered 1,101 differentially expressed genes, with enrichment in two-component systems, glycolysis/gluconeogenesis, and ABC transporters. Within CAZymes, GH1 genes (bglC, bglA, bglH, GYO_RS25640) and AA genes (cotA, glcD) were significantly upregulated under NH₄Cl-N1; RT-qPCR corroborated these trends. Correlation analysis further demonstrated significant positive associations between the expression of bglH and GYO_RS25640 correlated positively with β-glucosidase, filter paperase, and lignin peroxidase activities, and negatively with hemicellulose and lignin contents. Overall, this study revealed the regulatory mechanisms by which nitrogen form and concentration modulate lignocellulose degradation pathways in Bacillus subtilis LP-10, providing important references for the microbial-mediated utilization of lignocellulosic biomass resources in forest litter.