Identification chemoreceptor for D-malic acid, an unnatural occurred form, in Ralstonia solanacearum
1Hiroshima Univ., Grad. Sch. Adv. Sci. Matt.
Ralstonia solanacearum, a soil-borne gram-negative bacterium, causes bacterial wilt disease in many economically important corps worldwide including tomato, potato, tobacco etc. Chemotaxis allows R. solanacearum to locate the host root and efficiently migrate to it which is considered as critical early step for both invasion and colonization. Due to this fact, our laboratory attempt to functionally annotate and characterize chemoreceptors in this pathogen. From the genome sequence database, R. solanacearum has a complex chemosensory system with 22 methyl-accepting chemotaxis proteins (MCPs). The pathogen exhibit capability to move toward various organic acids and amino acids. Here, we report highly positive chemotaxis response of R. solanacearum toward D-malic acid which is very unique, since D-malic acid is unnatural occurred form and cannot support the growth of this pathogen. Moreover, bacterial chemotaxis toward D-malic acid has never been described. By screening single chemoreceptor mutant library and complementation analysis, we were able to identify one chemoreceptor for D-malic acid, which is Mcp3. Besides, Mcp3 was also the sole receptor distinguishing taxis toward L-tartaric acid, which has similar chemical structure and three-dimensional orientation with D-malic acid. To further identify the other chemoreceptors for D-malic acid, double mutants were constructed. A double mutant of mcp3 and mcpM, which is identified as L-malic acid chemoreceptor, showed nearly no response toward D-malic acid. Therefore, at least two chemoreceptors, Mcp3 and McpM, are responsible for sensing D-malic acid in R. solanacearum.