Campylobacter jejuniis a leading cause of diarrheal disease in humans and an intestinal commensal in poultry and other agriculturally important animals. These zoonotic infections result in significant amounts ofC. jejunipresent in the food supply to contribute to disease in humans. We previously found that a transposon insertion inCjj81176_1038, encoding a homolog of theEscherichia coliLivJ periplasmic binding protein of the leucine, isoleucine, and valine (LIV) branched-chain amino acid transport system, reduced the commensal colonization capacity ofC. jejuni81-176 in chicks.Cjj81176_1038is the first gene of a six-gene locus that encodes homologous components of theE. coliLIV system. By analyzing mutants with in-frame deletions of individual genes or pairs of genes, we found that this system constitutes a LIV transport system inC. jejuniresponsible for a high level of leucine acquisition and, to a lesser extent, isoleucine and valine acquisition. Despite each LIV protein being required for branched-chain amino acid transport, only the LivJ and LivK periplasmic binding proteins were required for wild-type levels of commensal colonization of chicks. All LIV permease and ATPase components were dispensable forin vivogrowth. These results suggest that the biological functions of LivJ and LivK for colonization are more complex than previously hypothesized and extend beyond a role for binding and acquiring branched-chain amino acids during commensalism. In contrast to other studies indicating a requirement and utilization of other specific amino acids for colonization, acquisition of branched-chain amino acids does not appear to be a determinant forC. jejuniduring commensalism.
Isolation of the braZ gene encoding the carrier for a novel branched-chain amino acid transport system in Pseudomonas aeruginosa PAO.
