4.2 Article

Identification and characterization of chemosensors for D-malate, unnatural enantiomer of malate, in Ralstonia pseudosolanacearum

Journal

MICROBIOLOGY-SGM
Volume 163, Issue 2, Pages 233-242

Publisher

MICROBIOLOGY SOC
DOI: 10.1099/mic.0.000408

Keywords

chemotaxis; D-malate; Ralstonia pseudosolanacearum; methyl-accepting chemotaxis protein; plant infection; bacterial wilt disease

Categories

Funding

  1. Japan Society for Promotion of Science
  2. Grants-in-Aid for Scientific Research [15H04478] Funding Source: KAKEN

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Ralstonia pseudosolanacearum Ps29 is attracted by nonmetabolizable D-malate, an unnatural enantiomer. Screening of a complete collection of single-mcp-gene deletion mutants of Ps29 revealed that the RSc1156 homologue is a chemosensor for D-malate. An RSc1156 homologue deletion mutant of Ps29 showed decreased but significant responses to D-malate, suggesting the existence of another D-malate chemosensor. McpM previously had been identified as a chemosensor for L-malate. We constructed an RSc1156 homologue mcpM double deletion mutant and noted that this mutant failed to respond to D-malate; thus, the RSc1156 homologue and McpM are the major chemosensors for D-malate in this organism. To further characterize the ligand specificities of the RSc1156 homologue and McpM, we constructed a Ps29 derivative (designated K18) harbouring deletions in 18 individual mcp genes, including mcpM and RSc1156. K18 harbouring the RSc1156 homologue responded strongly to L-tartrate and D-malate and moderately to D-tartrate, but not to L-malate or succinate. K18 harbouring mcpM responded strongly to L-malate and D-tartrate and moderately to succinate, fumarate and D-malate. Ps29 utilizes L-malate and L-tartrate, but not D-malate. We therefore concluded that L-tartrate and L-malate are natural ligands of the RSc1156 homologue and McpM, respectively, and that chemotaxis toward D-malate is a fortuitous response by the RSc1156 homologue and McpM in Ps29. We propose re-designation of the RSc1156 homologue as McpT. In tomato plant infection assays, the mcpT deletion mutant of highly virulent R. pseudosolanacearum MAFF106611 was as infectious as wildtype MAFF106611, suggesting that McpT-mediated chemotaxis does not play an important role in tomato plant infection.

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