Stress Tolerance and Virulence-Related Roles of Lipopolysaccharide in .

The lipopolysaccharide (LPS) composed of lipid A, core, and O-antigen is the fundamental constituent of the outer membrane in gram-negative bacteria. This study was conducted to investigate the roles of LPS in , the phytopathogen causing bacterial panicle blight and seedling rot in rice. To study the roles of the core oligosaccharide (OS) and the O-antigen region, mutant strains targeting the and the genes were generated. The LPS profile was greatly affected by disruption of the gene and slight reductions were observed in the O-antigen region following deletions. The results indicated that disruption in the core OS biosynthesis-related gene, , was associated with increased sensitivity to environmental stress conditions including acidic, osmotic, saline, and detergent stress, and to polymyxin B. Moreover, significant impairment in the swimming and swarming motility and attenuation of bacterial virulence to rice were also observed in the -defective mutant. The motility and virulence of O-antigen mutants defective in any gene of the operon, were not significantly different from the wild-type except in slight decrease in swimming and swarming motility with deletion. Altogether, the results of present study indicated that the LPS, particularly the core OS region, is required for tolerance to environmental stress and full virulence in . To our knowledge, this is the first functional study of LPS in a plant pathogenic sp. and presents a step forward toward full understanding of pathogenesis.