Role of the Na + -translocating NADH:quinone oxidoreductase in voltage generation and Na + extrusion in Vibrio cholerae

Abstract

For Vibrio cholerae, the coordinated import and export of Na(+) is crucial for adaptation to habitats with different osmolarities. We investigated the Na(+)-extruding branch of the sodium cycle in this human pathogen by in vivo (23)Na-NMR spectroscopy. The Na(+) extrusion activity of cells was monitored after adding glucose which stimulated respiration via the Na(+)-translocating NADH:quinone oxidoreductase (Na(+)-NQR). In a V. cholerae deletion mutant devoid of the Na(+)-NQR encoding genes (nqrA-F), rates of respiratory Na(+) extrusion were decreased by a factor of four, but the cytoplasmic Na(+) concentration was essentially unchanged. Furthermore, the mutant was impaired in formation of transmembrane voltage (ΔΨ, inside negative) and did not grow under hypoosmotic conditions at pH8.2 or above. This growth defect could be complemented by transformation with the plasmid encoded nqr operon. In an alkaline environment, Na(+)/H(+) antiporters acidify the cytoplasm at the expense of the transmembrane voltage. It is proposed that, at alkaline pH and limiting Na(+) concentrations, the Na(+)-NQR is crucial for generation of a transmembrane voltage to drive the import of H(+) by electrogenic Na(+)/H(+) antiporters. Our study provides the basis to understand the role of the Na(+)-NQR in pathogenicity of V. cholerae and other pathogens relying on this primary Na(+) pump for respiration.

Metabolic Reprogramming of Vibrio cholerae Impaired in Respiratory NADH Oxidation Is Accompanied by Increased Copper Sensitivity

“…Comparison of the growth behavior of V. cholerae with that of the corresponding nqr deletion strain on mixed amino acids at high salt concentrations revealed that lack of the NQR did not affect initial growth rates but diminished final growth yield (6,13). However, the NQR was mandatory for growth under alkaline, hypoosmotic conditions, and it was demonstrated that the in vivo function of NQR is to maintain the transmembrane voltage rather than to establish a chemical Na ϩ gradient (13). In a suckling mouse model of infection, the persistence of V. cholerae depended on the NQR (14).…”

The Na + -Translocating NADH:Quinone Oxidoreductase Enhances Oxidative Stress in the Cytoplasm of Vibrio cholerae

“…The addition of 0.1 mM arabinose to the growth medium resulted in a slight increase in the final cell yield with the reference strain (Fig. 7), perhaps caused by an increase in membrane potential generated by the Na ϩ -NQR (49). Increasing the arabinose concentration to 1 mM and 10 mM did not affect the reference strain but led to a decrease in final cell densities of V. cholerae ⌬oxyR/pNqr1 by 11% (1 mM arabinose) and 26% (10 mM arabinose) compared to V. cholerae/pNqr1 (Fig.…”

The microbiome as a biosensor: functional profiles elucidate hidden stress in hosts

“…In many alkaline environments, NQR constructs the primary sodium efflux system through oxidation of NADH and reduction of quinone. This process creates an electrochemical gradient of net negative charge in the cytosol (51), and the gradient is used by cation/proton antiporters ( e.g., Na + /H + , and K + /H + ) to exchange non-balanced movement of positive charge (H + ) to the cell (more protons enter the cytoplasm as compared to the efflux of sodium or potassium ions (49, 51, 52, 53). In a global mapping of soil bacterial communities, cation/proton antiporters were observed to be key genes overrepresented in dryland soil, presumably due to the high levels of salt and pH in arid soils (54).…”

“…To the best of our knowledge, no prior study has linked environmental microbiome functions to pH level or salinity. However, the association between our significantly differentiated genes to processing specific environmental conditions is established in vitro in numerous studies (51, 63). Here, we hypothesized that differentially abundant genes could be used as predictive markers of environmental cue, and this hypothesis is supported by meta-analyses demonstrating a link between single isolate studies and microbial communities in vivo .…”