Contribution of the Gene Encoding Glutamate Racemase in the Motility and Virulence of .

Bacterial traits for virulence of causing lethal wilt in plants were extensively studied but are not yet fully understood. Other than the known virulence factors of , this study aimed to identify the novel gene(s) contributing to bacterial virulence of . Among the transposon-inserted mutants that were previously generated, we selected mutant SL341F12 strain produced exopolysaccharide equivalent to wild type strain but showed reduced virulence compared to wild type. In this mutant, a transposon was found to disrupt the gene encoding glutamate racemase which converts L-glutamate to D-glutamate. SL341F12 lost its motility, and its virulence in the tomato plant was markedly diminished compared to that of the wild type. The altered phenotypes of SL341F12 were restored by introducing a full-length gene. The expression of genes required for flagella assembly was significantly reduced in SL341F12 compared to that of the wild type or complemented strain, indicating that the loss of bacterial motility in the mutant was due to reduced flagella assembly. A dramatic reduction of the mutant population compared to its wild type was apparent (, root) than its wild type but not in soil and rhizosphere. This may contribute to the impaired virulence in the mutant strain. Accordingly, we concluded that in may be involved in controlling flagella assembly and consequently, the mutation affects bacterial motility and virulence.