Genomic and structural insights into cazymes & novel AA10 lytic polysaccharide mono-oxygenase from Serratia marcescens CRi_33 for efficient lignocellulosic biomass deconstruction

Abstract

Lignocellulosic biomass (LCB) saccharification remains a key challenge for cost-effective value-added products due to structural intricacy. Lytic polysaccharide mono-oxygenase (LPMOs) catalyses the glycosidic bonds cleavage oxidatively in crystalline polysaccharides, facilitating synergistic action with glycoside hydrolases (GHs). While fungal and actinobacterial LPMOs are well studied, bacterial LPMOs, especially in Gram-negative Serratia, are underexplored. The study investigates Serratia marcescens CRi_33 for its LCB deconstruction potential through enzymatic and genomic analyses. The strain exhibited elevated β-glucuronidase activity of 0.54 U/mL, endo-1,4-β-xylanase of 0.41 U/mL, and arabinosidase of 0.48 U/mL, reflecting strong hemicellulolytic potential. CRi_33-derived enzyme concentrate with biotin and cellobiose supplementation, released 152.04 mg/g of reducing sugars from pre-treated wheat straw (WS). FeCl₃ supplementation further enhanced saccharification to 165.04 ± 3.44 mg/g, resulting in an 8.55% increase. Genome analysis revealed 239 CAZymes, including 120 GHs and 11 auxiliary activity enzymes like laccases (AA1), lignin peroxidases (AA2), and benzoquinone reductases (AA6). Notably, a unique AA10 family LPMO, SmrLPMO10A, possessing a GlcNAc-binding domain, was structurally characterized. Structural modeling confirmed a conserved histidine brace, and docking studies showed strong binding affinity of -5.1 kcal/mol to hemicellulosic sugars, particularly galactose and mannose. This suggests dual specificity for chitin and hemicellulose, which is limited and less explored previously in Serratia LPMOs. These findings fill a critical gap in bacterial LPMO knowledge and highlights S. marcescens CRi_33’s efficiency for sustainable waste valorization and biorefinery applications.