Identification and characterization of a methyl-accepting chemotaxis protein in Ralstonia pseudosolanacearum using chemically undefined materials.

Ralstonia pseudosolanacearum is a plant-pathogenic bacterium that causes bacterial wilt in economically important crops. Chemotaxis is required for full virulence in R. pseudosolanacearum. R. pseudosolanacearum Ps29 possesses 20 methyl-accepting chemotaxis proteins (MCPs) and 2 MCP-like chemoreceptors. To understand the role of chemotaxis in plant infection, we are characterizing the functions of these 20 MCPs. Out of 20 MCPs, 8 MCPs have been characterized. To characterize the remaining MCPs, we deleted the 8 genes encoding characterized MCPs in R. pseudosolanacearum Ps29 to construct R. pseudosolanacearum D8. R. pseudosolanacearum D8 was examined for chemotactic responses to several chemically undefined materials including vegetable juices and tryptic soy broth (TSB) to find attractants. R. pseudosolanacearum D8 showed strong responses to green pepper and carrot juices and TSB. We constructed a mutant library of R. pseudosolanacearum D8 by deleting each of the MCP genes. Chemotaxis assays to TSB revealed that an MCP which we named McpD was responsible for sensing an attractant(s) in TSB. Because amino acids are the major constituents of TSB, we measured chemotactic responses of R. pseudosolanacearum D8 to 20 proteinogenic amino acids and found Asp and Glu as the major attractants of McpD and Cys as the minor attractant. R. pseudosolanacearum Ps29 can utilize Asp and Glu as sole carbon and nitrogen sources, suggesting that the role of McpD-mediated chemotaxis is finding growth substrates.