DsrCis involved in fermentative growth and interacts directly with theFlxABCD–HdrABCcomplex inDesulfovibrio vulgarisHildenborough

Abstract

DsrC is a key protein in dissimilatory sulfur metabolism, where it works as co-substrate of the dissimilatory sulfite reductase DsrAB. DsrC has two conserved cysteines in a C-terminal arm that are converted to a trisulfide upon reduction of sulfite. In sulfate-reducing bacteria, DsrC is essential and previous works suggested additional functions beyond sulfite reduction. Here, we studied whether DsrC also plays a role during fermentative growth of Desulfovibrio vulgaris Hildenborough, by studying two strains where the functionality of DsrC is impaired by a lower level of expression (IPFG07) and additionally by the absence of one conserved Cys (IPFG09). Growth studies coupled with metabolite and proteomic analyses reveal that fermentation leads to lower levels of DsrC, but impairment of its function results in reduced growth by fermentation and a shift towards more fermentative metabolism during sulfate respiration. In both respiratory and fermentative conditions, there is increased abundance of the FlxABCD-HdrABC complex and Adh alcohol dehydrogenase in IPFG09 versus the wild type, which is reflected in higher production of ethanol. Pull-down experiments confirmed a direct interaction between DsrC and the FlxABCD-HdrABC complex, through the HdrB subunit. Dissimilatory sulfur metabolism, where sulfur compounds are used for energy generation, is a key process in the ecology of anoxic environments, and is more widespread among bacteria than previously believed. Two central proteins for this type of metabolism are DsrAB dissimilatory sulfite reductase and its co-substrate DsrC. Using physiological, proteomic and biochemical studies of Desulfovibrio vulgaris Hildenborough and mutants affected in DsrC functionality, we show that DsrC is also relevant for fermentative growth of this model organism and that it interacts directly with the soluble FlxABCD-HdrABC complex that links the NAD(H) pool with dissimilatory sulfite reduction.

Combining metabolic flux analysis with proteomics to shed light on the metabolic flexibility: the case of Desulfovibrio vulgaris Hildenborough

“…Alternatively, during fermentation, the complex might work in reverse thus dissipating the excess of reducing equivalents toward ethanol production with NADH. The NAD + produced is recycled by Flx complex with electrons coming from reduced ferredoxin and DsrC through Hdr complex (Ramos et al, 2015;Ferreira et al, 2023). Interestingly, according to the present study no intracellular flux for ethanol pathway was simulated using the iDvu71 model.…”

“…The two electrons generated from NADH reoxidation by the Flx complex are then transferred through the Hdr complex to the ferredoxin pool and an unknow electron acceptor (Pereira et al, 2008;Ramos et al, 2015). It was recently proposed that DsrC might serve as electron acceptor, thus providing electrons required for sulfate reduction, while reduced ferredoxin will serve as donor for hydrogen production by membrane-associated hydrogenases (Ech or Coo) for hydrogenase production and the generation of protons gradient (Ferreira et al, 2023). Alternatively, during fermentation, the complex might work in reverse thus dissipating the excess of reducing equivalents toward ethanol production with NADH.…”

Physiological potential and evolutionary trajectories of syntrophic sulfate-reducing bacterial partners of anaerobic methanotrophic archaea

“…In addition to the most likely pathways of electron transfer in the syntrophic SRB, as established using transcriptomic data on ANME/SRB partnership [24,25] (Figs 2 and 3), other inner membrane complexes exist in these genomes that may provide additional respiratory flexibility. HotSeep-1 genomes contain a complex that involves an HdrA subunit and a protein that also binds hemes c and contains a CCG domain similar to that found in HdrB and TmcB predicted to interact with DsrC [70,74]. This complex a putative cytochrome c oxidoreductase containing a CCG domain, would likely transfer electrons from cytochromes c to the DsrC (AMM42179.1-AMM42180.1) or perhaps to a ferredoxin.…”

Stepwise pathway for early evolutionary assembly of dissimilatory sulfite and sulfate reduction

“…The other side is dominated by Thermodesulfobacteria and Deltaproteobacteria including the Desulfovibrio vulgaris Hildenborough DsrC sequence. Recently, it was experimentally shown that, besides being involved in Dsr metabolism, D. vulgaris Hildenborough DsrC also interacts with the FlxABCD-HdrABC complex during fermentative growth [47]. The involvement in other metabolic processes might lead to functional changes that are reflected in the phylogeny by this clade separation.…”