Identification of the mcpA and mcpM Genes, Encoding Methyl-Accepting Proteins Involved in Amino Acid and l -Malate Chemotaxis, and Involvement of McpM-Mediated Chemotaxis in Plant Infection by Ralstonia pseudosolanacearum (Formerly Ralstonia solanacearum Phylotypes I and III)

Sequence analysis has revealed the presence of 22 putative methyl-accepting chemotaxis protein (mcp ) genes in theRalstonia pseudosolanacearum GMI1000 genome. PCR analysis and DNA sequencing showed that the highly motileR. pseudosolanacearum strain Ps29 possesses homologs of all 22R. pseudosolanacearum GMI1000mcp genes. We constructed a complete collection of singlemcp gene deletion mutants ofR. pseudosolanacearum Ps29 by unmarked gene deletion. Screening of the mutant collection revealed thatR. pseudosolanacearum Ps29 mutants of RSp0507 and RSc0606 homologs were defective in chemotaxis tol -malate and amino acids, respectively. RSp0507 and RSc0606 homologs were designatedmcpM andmcpA . While wild-typeR. pseudosolanacearum strain Ps29 displayed attraction to 16 amino acids, themcpA mutant showed no response to 12 of these amino acids and decreased responses to 4 amino acids. We constructedmcpA andmcpM deletion mutants of highly virulentR. pseudosolanacearum strain MAFF106611 to investigate the contribution of chemotaxis tol -malate and amino acids to tomato plant infection. Neither single mutant exhibited altered virulence for tomato plants when tested by root dip inoculation assays. In contrast, themcpM mutant (but not themcpA mutant) was significantly less infectious than the wild type when tested by a sand soak inoculation assay, which requires bacteria to locate and invade host roots from sand. Thus, McpM-mediated chemotaxis, possibly reflecting chemotaxis tol -malate, facilitatesR. pseudosolanacearum motility to tomato roots in sand.