Roles of the chemotaxis and the motility by flagella on environmental response of Vibio cells

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Vibrio cholerae has 3 sets of general chemotactic signaling proteins (Che proteins) and 45 chemoreceptor-like proteins (referred to as MLPs). Systems I cluster and III cluster in the chromosome have 4 mlp genes and 2 mlp genes, respectively, and we speculated that those genes were coupled CheAl and CheA3. System II cluster does not have mlp genes. To estimate the mlp genes coupled to any of the three Che systems, the primary sequences were analyzed and 19 MLPs have a similarity to MLPs of V. parahemolyticas which have only one CheA homologous to CheA2 of V. *cholerae. The 19 MLPs are candidates to couple with CheA2. To evaluate the assumption, the methylation of MLP by the homologous product of the methyl transfer enzyme CheR was examined. The similar motif as the CheR binding sequence of E. coli MCP was found in the C terminal region of M1p01 and M1p45, and CheR3 has the highest similarity to E. coli CheR among the three of the CheR homologs. This motif might give a binding site of CheR2 and is important for metylation of MLP coupled to the putative CheA2. Next, we examined the localization of Che system components by using their GFP fusion constructs. We detected that the Che proteins and MLPs of system II localize to the flagellated pole and some of the components of systems I were also shown to localize to the flagellated pole. During these observations, we noticed that the system I components were diffused under some conditions. When cells were grown to late logarithmic phase with vigorous shaking, CheAl and CheY2 did not localize but further incubation without shaking induced their polar localization. Moreover, when the air was replaced with nitrogen gas, shaking allowed their polar localization. Inhibitors of respiration also induced their polar localization. These results indicate that certain state of energy metabolism induces polar localization of CheAl and CheY2, raising the possibility that system I may work under microanaerobic conditions.