Chemoreceptor VfcA Mediates Amino Acid Chemotaxis in Vibrio fischeri

Abstract

ABSTRACTFlagellar motility and chemotaxis byVibrio fischeriare important behaviors mediating the colonization of its mutualistic host, the Hawaiian bobtail squid. However, none of the 43 putative methyl-accepting chemotaxis proteins (MCPs) encoded in theV. fischerigenome has been previously characterized. Using both an available transposon mutant collection and directed mutagenesis, we isolated mutants for 19 of these genes, and screened them for altered chemotaxis to six previously identified chemoattractants. Only one mutant was defective in responding to any of the tested compounds; the disrupted gene was thus namedvfcA(VibriofischerichemoreceptorA; locus tag VF_0777). In soft-agar plates, mutants disrupted invfcAdid not exhibit the serine-sensing chemotactic ring, and the pattern of migration in the mutant was not affected by the addition of exogenous serine. Using a capillary chemotaxis assay, we showed that, unlike wild-typeV. fischeri, thevfcAmutant did not undergo chemotaxis toward serine and that expression ofvfcAon a plasmid in the mutant was sufficient to restore the behavior. In addition to serine, we demonstrated that alanine, cysteine, and threonine are strong attractants for wild-typeV. fischeriand that the attraction is also mediated by VfcA. This study thus provides the first insights into howV. fischeriintegrates information from one of its 43 MCPs to respond to environmental stimuli.