Genomic insights into multidrug and heavy metal resistance in Chryseobacterium sp. BI5 isolated from sewage sludge

• vanT in vanG cluster links vancomycin resistance to biofilm formation. • Pan genomic insights reveals dual resistance to antibiotics and heavy metals. • Mobilome analysis highlights genomic islands driving resistance gene transfer. • Findings underscore AMR risks in sewage sludge-based agricultural practices. Multidrug-resistant (MDR) bacteria in environmental reservoirs pose significant threats to public health. In this study, Chryseobacterium sp. BI5, an MDR strain, was isolated from dried sewage sludge used as fertilizer. Whole-genome sequencing (WGS) revealed a 4.79 Mb genome with 305 antimicrobial resistance genes (ARGs), including blaNDM, vanT , and EmrA , alongside heavy metal resistance determinants such as czcABC and mntH . Phylogenetic and digital DNA-DNA hybridization (dDDH) analysis confirmed BI5 as a novel species, with the highest dDDH value (51.5 %) to Chryseobacterium paridis YIM B02567. Comparative pangenome analysis identified 24 unique gene clusters, including two linked to drug metabolism. Phenotypically, BI5 exhibited strong biofilm formation, high hydrophobicity (>70 % for multiple solvents), and significant survival under simulated gastrointestinal conditions. Growth kinetics under heavy metal stress showed enhanced tolerance up to 5 mM Zn²⁺ and Cd²⁺. Mobilome analysis identified insertion sequences (IS) and genomic islands (GIs) harboring genes linked to virulence, resistance, and environmental resilience, suggesting horizontal gene transfer (HGT). The potential of dried sewage sludge to disseminate these resistance traits through agricultural application necessitates urgent monitoring and regulatory measures. These findings contribute to the limited knowledge of Chryseobacterium species, emphasizing the uniqueness of this isolate and shedding light on its role in the global AMR landscape.