Comparative Genomics of a Hemolymph-Derived Pseudomonas boreofloridensis Strain RAC1 Reveals Metabolic Versatility and Multidrug Resistance

Abstract

Flacherie is a major bacterial disease compromising silkworm health and cocoon productivity; however, the diversity and genomic features of larva-associated pathogens remain poorly characterized. In the present study, we isolated and characterized a Gram-negative bacterium, designated as Pseudomonas boreofloridensis strain RAC1, from the hemolymph of silkworm larvae with flacherie symptoms. The isolate exhibited clear swimming motility, indicating an active flagellar system. Biochemical profiling using the VITEK-2 platform revealed broad metabolic capabilities, including utilization of multiple organic acids and amino-acids, related enzymatic activities, highlighting its adaptability under nutrient-variable host conditions. Chemotaxonomic analysis using fatty acid methyl ester (FAME) profiling further supported its identity within the genus Pseudomonas. Whole-genome sequencing showed a 4.49 Mb GC-rich genome encoding diverse functional pathways related to central metabolism, aromatic compound degradation, and carbohydrate-active enzymes, suggesting strong ecological flexibility. Importantly, genomic screening identified virulence-associated gene and multiple antimicrobial resistance determinants, dominated by efflux pumps and outer membrane permeability factors. In addition, strain RAC1 contained several mobile genetic elements and three prophage regions, reflecting a highly plastic genome. Pangenome analysis across related Pseudomonas strains indicated an open pangenome, driven largely by accessory and cloud genes. Overall, P. boreofloridensis RAC1 represents a multidrug-resistant and genomically dynamic strain encoding virulence-associated genes and resistance genes. These genomic features suggest adaptive potential in host-associated environments and require further experimental investigation to evaluate its role in silkworm larval disease.