<i>Lactobacillus plantarum</i> WCFS1 Electron Transport Chains

<jats:title>ABSTRACT</jats:title> <jats:p> <jats:italic>Lactobacillus plantarum</jats:italic> WCFS1 requires both heme and menaquinone to induce respiration-like behavior under aerobic conditions. The addition of these compounds enhanced both biomass production, without progressive acidification, and the oxygen consumption rate. When both heme and menaquinone were present, <jats:italic>L. plantarum</jats:italic> WCFS1 was also able to reduce nitrate. The ability to reduce nitrate was severely inhibited by the glucose levels that are typically found in <jats:italic>L. plantarum</jats:italic> growth media (1 to 2% [vol/vol] glucose). In contrast, comparable mannitol levels did not inhibit the reduction of nitrate. <jats:italic>L. plantarum</jats:italic> reduced nitrate with concomitant formation of nitrite and ammonia. Genes that encode a <jats:italic>bd</jats:italic> -type cytochrome ( <jats:italic>cydABCD</jats:italic> ) and a nitrate reductase ( <jats:italic>narGHJI</jats:italic> ) were identified in the genome of <jats:italic>L. plantarum</jats:italic> . The <jats:italic>narGHJI</jats:italic> operon is part of a cluster of genes that includes the molybdopterin cofactor biosynthesis genes and <jats:italic>narK</jats:italic> . Besides a menaquinone source, isogenic mutants revealed that <jats:italic>cydA</jats:italic> and <jats:italic>ndh1</jats:italic> are required for the aerobic-respiration-like response and <jats:italic>narG</jats:italic> for nitrate reduction. The <jats:italic>ndh1</jats:italic> mutant was still able to reduce nitrate. The existence of a nonredundant branched electron transport chain in <jats:italic>L. plantarum</jats:italic> WCFS1 that is capable of using oxygen or nitrate as a terminal electron acceptor is proposed. </jats:p>