Journal
APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Volume 72, Issue 1, Pages 695-701Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/AEM.72.1.695-701.2006
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Two transmembrane proteins were tentatively classified as NarK1 and NarK2 in the Pseudomonas genome project and hypothesized to play an important physiological role in nitrate/nitrite transport in Pseudomonas aeruginosa. The narK1 and narK2 genes are located in a cluster along with the structural genes for the nitrate reductase complex. Our studies indicate that the transcription of all these genes is initiated from a single promoter and that the gene complex narK1K2GHJI constitutes an operon. Utilizing an isogenic narK1 mutant, a narK2 mutant, and a narK1K2 double mutant, we explored their effect on growth under denitrifying conditions. While the Delta narK1::Gm mutant was only slightly affected in its ability to grow under denitrification conditions, both the Delta narK2::Gm and Delta narK1K2::Gm mutants were found to be severely restricted in nitrate-dependent, anaerobic growth. All three strains demonstrated wild-type levels of nitrate reductase activity. Nitrate uptake by whole-cell suspensions demonstrated both the Delta narK2::Gm and Delta narK1K2::Gm mutants to have very low yet different nitrate uptake rates, while the Delta narK1::Gm mutant exhibited wild-type levels of nitrate uptake. Finally, Escherichia coli narK rescued both the Delta narK2::Gm and Delta narK1K2::Gm mutants with respect to anaerobic respiratory growth. Our results indicate that only the NarK2 protein is required as a nitrate/nitrite transporter by Pseudomonas aeruginosa under denitrifying conditions.
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