A Dual Role of Amino Acids from Seed Exudates in the Chemotaxis Response of ORS571.

ORS571 can induce nodule formation on the roots and the stems of its host legume, . Plant exudates are essential in the dialogue between microbes and their host plant and, in particular, amino acids can play an important role in the chemotactic response of bacteria. Histidine, arginine, and aspartate, which are the three most abundant amino acids present in seed exudates, behave as chemoattractants toward . A position-specific-iterated BLAST analysis of the methyl-accepting chemotaxis proteins (MCPs) (chemoreceptors) in the genome of was performed. Among the 43 MCP homologs, two MCPs harboring a dCache domain were selected as possible cognate amino acid MCPs. After analysis of relative gene expression levels and construction of a gene-deleted mutant strain, one of them, AZC_0821 designed as TlpH, was confirmed to be responsible for the chemotactic response to the three amino acids. In addition, it was found that these three amino acids can also influence chemotaxis of independently of the chemosensory receptors, by being involved in the increase of the expression level of several and genes involved in the chemotaxis pathway and flagella synthesis. Thus, the contribution of amino acids present in seed exudates is directly related to the role as chemoattractants and indirectly related to the role in the regulation of expression of key genes involved in chemotaxis and motility. This "dual role" is likely to influence the formation of biofilms by and the host root colonization properties of this bacterium.