Characterization of the Na⁺-transporting NADH:ubiquinone oxidoreductase (NQR) in Vibrio cholerae

Abstract

We previously reported that inhibition of the Na⁺ translocating NADH:ubiquinone oxidoreductase (NQR), either by chemical inhibition or mutation, increased toxT transcription in Vibrio cholerae. In this study, we revealed that the nqr mutant strain showed similar phenotypes as the Escherichia coli NADH dehydrogenase I (nuo) mutant strain (e.g. growth defect after the mid log growth phase and higher acetic acid production). The increased growth and toxT expression in the nqr mutant relative to the wild type strain appears to be growth phase dependent. However, after longer growth, nqr showed lower amounts of cholera toxin production compared to the parent strain. Interestingly, the nqr mutant strain showed a similar level of toxT expression in the presence of L-lactate, which is known to stimulate respiration. Through Biolog® Phenotype Microarray (PM) analysis, we found that the V. cholerae nqr mutant strain had defects in a broad spectrum of metabolism functions, including amino acid, carboxylic acid, phosphorus, and sulfur utilization, indicating an important role of NQR in V. cholerae metabolism. In addition, nqr mutation increased osmotic sensitivity in V. cholerae. Some of the defects identified by PM analysis, including NaCl sensitivity, were restored by the addition of L-lactate.