Genome-and structure-guided mechanism of carboxymethyl cellulose and straw degradation by a marine sediment bacterium Mycobacterium sp. CBM1

Straw is an abundant renewable biomass resource, yet its microbial valorization remains constrained by lignocellulose recalcitrance and the limited characterization of cellulolytic bacteria from coastal and marine environments. Here, we isolated a novel cellulolytic strain, Mycobacterium sp. CBM1, from nearshore sediment in Liaodong Bay (China) using sodium carboxymethyl cellulose (CMC Na) as the sole carbon source. Congo red staining and 16S rRNA sequencing confirmed its cellulolytic phenotype and taxonomic identity. Enzyme assays demonstrated endoglucanase, exoglucanase, and β-glucosidase activities, with optimal production at pH 7, 2% salinity, NH 4 Cl as the nitrogen source, and CMC-Na (300–600 mPa·s) at 0.5 g/L. When cultivated with straw as the sole carbon source (5 g/L), CBM1 converted ∼20% of the substrate within 30 days, accompanied by a decrease in crystallinity index from 46.63% to 37.12%. Whole-genome sequencing revealed a CAZyme repertoire of 230 genes, including 76 glycoside hydrolases, supporting reconstruction of a putative cellulose degradation route. Structural modeling and molecular docking provided supportive hypotheses for substrate recognition by key cellulases. Collectively, these results provide a phenotype-genome-structure basis for developing bacterial candidates for sustainable straw bioconversion.