Impact of Na+ -translocating NADH:quinone oxidoreductase (NQR) on iron uptake and nqrM expression in Vibrio cholerae  [23.11.19]

For bacteria, iron is an essential nutrient that helps to maintain vital functions of a variety of enzymes, such as ribonucleotide reductase (synthesis of DNA precursors) or proteins in the respiratory chain. Hohenheim scientists examined the iron metabolism of the Cholera pathogen (Vibrio cholerae) and could show how this pathogen survives in unfavorable, iron-limited environments such as its human host. A recent study describes the role of the NQR protein complex in iron metabolism, making this it an interesting and new target for a novel type of antibiotics.

The Na+ -translocating NADH:quinone oxidoreductase (NQR) generates an electrochemical Na+ gradient in vivo which is crucial for expulsion of bactericidal drugs by secondary efflux systems. Moreover, this respiratory Na+ pump is the major catabolic NADH dehydrogenase required for the regeneration of NAD+. Electrons are delivered to ubiquinone (Q) which is reduced to ubiquinol (QH2), a substrate for downstream respiratory complexes.

 

Agarwal S1, Bernt M1, Toulouse C1, Kurz H2, Pfannstiel J3, D'Alvise P4, Hasselmann M4, Aagesen AM5, Häse CC5, Fritz G1, Steuber J6 (2019) Impact of Na+ -translocating NADH:quinone oxidoreductase (NQR) on iron uptake and nqrM expression in Vibrio cholerae. J Bacteriol. 2019 Nov 11. pii: JB.00681-19. doi: 10.1128/JB.00681-19. [Epub ahead of print]

Author information

1 Institute of Microbiology, University of Hohenheim, Stuttgart, Germany.

2 Core Facility Hohenheim, Analytical Chemistry Core Facility, University of Hohenheim, Stuttgart, Germany.

3 Core Facility Hohenheim, Mass Spectrometry Core Facility, University of Hohenheim, Stuttgart, Germany.

4 Institute of Animal Science, University of Hohenheim, Stuttgart, Germany.

5 Carlson College of Veterinary Medicine, Oregon State University, Corvallis, Oregon, United States of America.

6 Institute of Microbiology, University of Hohenheim, Stuttgart, Germany > julia.steuber@uni-hohenheim.de

Abstract

The Na+ - ion translocating NADH:quinone oxidoreductase (NQR) from Vibrio cholerae is a membrane bound respiratory enzyme which harbors flavins and Fe-S clusters as redox centers. The NQR is the main producer of sodium motive force (SMF) and drives energy-dissipating processes such as flagellar rotation, substrate uptake, ATP synthesis and cation-proton antiport. The NQR requires for its maturation besides the six structural genes, nqrABCDEF, a flavin attachment gene encoded by apbE and the nqrM gene, presumably a Fe delivery protein. We here describe growth studies and quantitative real time PCR for the V. cholerae O395N1 strain wildtype (wt) and its mutant strains, Δnqr and ΔubiC, impaired in respiration. In a comparative proteome analysis, FeoB, the membrane subunit of the uptake system for Fe2+ (Feo), was increased in V. cholerae Δnqr In this study, the upregulation is confirmed on the mRNA level, and results in improved growth rates of V. cholerae Δnqr with Fe2+ as iron source. We studied the expression of feoB on other respiratory enzyme deletion mutants like ΔubiC to identify if iron transport was specific to the absence of NQR resulted from impaired respiration. We show that the nqr operon comprises, besides the structural nqrABCDEF genes, the downstream apbE and nqrM genes on the same operon, and demonstrate induction of the nqr operon by iron in V. cholerae wt. In contrast, expression of the nqrM gene in V. cholerae Δnqr is repressed by iron. The lack of functional NQR has a strong impact on iron homeostasis in V. cholerae, and exemplifies that central respiratory metabolism is interwoven with iron uptake and regulation.Importance Investigating strategies of iron acquisition, storage and delivery in Vibrio cholerae is a prerequisite to understand how this pathogen thrives in hostile, iron-limited environments such as the human host. Besides highlighting the maturation of the respiratory complex NQR, this study points out the influence of NQR on iron metabolism thereby making it a potential drug target for antibiotics.


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The Na+ -translocating NADH:quinone oxidoreductase (NQR) generates an electrochemical Na+ gradient in vivo which is crucial for expulsion of bactericidal drugs by secondary efflux systems. Moreover, this respiratory Na+ pump is the major catabolic NADH dehydrogenase required for the regeneration of NAD+. Electrons are delivered to ubiquinone (Q) which is reduced to ubiquinol (QH2), a substrate for downstream respiratory complexes.