Lipopolysaccharide Biosynthesis-Related Genes, galU, ugd, waaC, waaG and waaL Are Required for Full Virulence of Pantoea ananatis.

Pantoea ananatis is a plant pathogen that causes center rot disease in onion. Lipopolysaccharide (LPS), a fundamental constituent of the outer membrane of Gram-negative bacteria, is instrumental in bacterial virulence. This study investigated the role of LPS in P. ananatis by analyzing the LPS biosynthesis-related genes, galU, ugd, waaC, waaG, and waaL. Deletion of each gene impaired LPS biosynthesis and reduced virulence. To understand the basis of this reduced virulence, we examined the deletion mutant phenotypes. Deletion of galU, ugd, waaC, or waaG reduced resistance to polymyxin B and sodium dodecyl sulfate, whereas deletion of waaL reduced resistance only to polymyxin B. All deletion mutants exhibited suppressed flagellar formation, decreased motility, and increased stress-response regulator gene rpoE expression. Furthermore, deletion of galU or waaC reduced pantaphos biosynthesis, a major pathogenicity factor in P. ananatis, and decreased the expression of the pantaphos biosynthetic gene hvrA. These findings indicate that galU, ugd, waaC, waaG, and waaL, through their roles in LPS formation, are required for the virulence of P. ananatis by influencing drug resistance, flagellar motility, and, in part, pantaphos biosynthesis.