Nathalie Payne – BIP – “Integrative study of hydrogen metabolism in Desulfovibrio fructosovorans: physiological role of the electron-bifurcating hydrogenase Hnd”

Nathalie Payne will defend her thesis on Friday 8 April at 2pm in the P. DESNUELLE amphitheatre on the Joseph Aiguier campus and by videoconference (link to come).

Abstract : Desulfovibrio fructosovorans, an anaerobic sulfate-reducing bacterium, possesses six gene clusters encoding six hydrogenases catalyzing the reversible oxidation of hydrogen gas (H₂) into protons and electrons. One of these is an electron-bifurcating hydrogenase Hnd, which couples the exergonic reduction of NAD⁺ to the endergonic reduction of a ferredoxin with electrons derived from H₂. It was previously hypothesized that its biological function involves the production of NADPH necessary for biosynthetic purposes. However, it was subsequently demonstrated that Hnd is instead a NAD⁺-reducing enzyme, thus its specific function has yet to be established. To understand the physiological role of Hnd in the energy metabolism in D. fructosovorans, we compared the hnd deletion mutant with the wild-type strain grown on pyruvate under different growth conditions. Our results indicate that the hnd operon is strongly regulated at the transcriptional level and that the deletion of hnd has a drastic effect on the expression of genes for two enzymes, an aldehyde:ferredoxin oxidoreductase and an alcohol dehydrogenase, as well as on the production of ethanol as a fermentation product. Additionally, Nuclear Magnetic Resonance-based metabolomics and quantitative label-free proteomics was used to probe the role of Hnd at a global level. The omics results establish that Hnd indirectly intervenes in global carbon metabolism and additional metabolic processes such as the biosynthesis of amino acids. Collectively, our results reveal that Hnd is profoundly involved in ethanol metabolism when bacteria grow in pyruvate fermentation and leading us to propose that Hnd oxidizes part of the H₂ produced during fermentation, thereby generating both NADH and reduced ferredoxin, and is involved in maintaining redox balance through its electron bifurcation mechanism.