IDENTIFICATION AND CHARACTERIZATION OF A NOVEL TRANSDUCER AND SOLUBLE RECEPTORS FOR AMINO ACID CHEMOTAXIS OF VIBRIO ALGINOLYTICUS

Vibrio alginolyticusv has two types of flagella, the polar flagellum (Pof) and the lateral flagella (Laf). In liquid, a rod-shaped swimmer cell is propelled by Pof, whereas on a surface, the cell differentiates into an elongated swarmer cell with numerous Laf. These cells respond differentially to cysteine: the former is attracted well but the latter is not. These flagella are regulated by a common Che system that involves at least 25 homologs of methyl-accepting chemotaxis proteins (MCPs) , which we name MCP-like protein (MLPs). VaMlp9 was found to mediate attractant responses to amino acids, including cysteine. The expression of vamlp9 in swarmer cells did not enhance their cysteine responses, suggesting the involvement of additional factor(s), such as a periplasmic binding protein, in cysteine taxis. The genome sequence of V. alginolyticus was therefore surveyed to find candidates of periplasmic amino acid binding proteins. These genes encoding putative amino acid binding proteins (VMC_08300, VMC_31200, VMC_35490 VMC_42120), when expressed in the V. alginolyticus swarmer cell, enhanced attractant responses to serine and cysteine, suggesting that these proteins serve as soluble chemoreceptors for serine and cysteine. Furthermore, co-overexpression of the VMC_42120 gene and vamlp9 gene showed that increase dramatically to attractant responses to cysteine. These results suggest that VaMlp9 is a transducer that requires this periplasmic cysteine-binding protein encoded by the VMC_42120 gene for cysteine taxis