Identification, heterologous expression of a PL8 family polysaccharide lyase Pmply8 from Bacillus mucilaginosus SM-01 and its specific degradation of BMPS

Polysaccharide lyases enable the highly specific and environmentally benign conversion of natural polysaccharides into high-value products, representing a pivotal sustainable biotechnology for biomass valorization. However, the screening and characterization of functional polysaccharide lyases from Bacillus mucilaginosus remain insufficient. In this study, four candidate genes were screened from the genome of B. mucilaginosus SM-01 based on the information of polysaccharide lyase family genes in NCBI database and sequence alignment. Phylogenetic analysis revealed that these enzymes cluster belong to the PL8, PL11, PL4, and PL11 families, respectively. Through cloning, expression, and enzymatic screening, PmPly8 (a PL8 family member) was identified as the sole enzyme capable of degrading the exopolysaccharide BMPS. Following purification via Ni‑NTA affinity chromatography, SDS‑PAGE confirmed its molecular weight of approximately 88 kDa with high purity. Biochemical characterization revealed an optimal activity at 55°C and pH 8.5. Enzyme activity was slightly enhanced by Na⁺ and Li⁺ but strongly inhibited by Cu²⁺, Zn²⁺, and Mg²⁺. The release of reducing sugars reached saturation within 4 h. Critically, LC‑MS/MS, FT‑IR, AFM, and TGA analyses collectively demonstrated that PmPLY8 efficiently cleaves Bacillus mucilaginosus polymeric substance (BMPS) into oligosaccharides, confirming its functional role in polysaccharide degradation. This study provides a theoretical basis and technical support for the industrial application of Pmply8 in the resource utilization of polysaccharides.