Energy conservation by a hydrogenase-dependent chemiosmotic mechanism in an ancient metabolic pathway

Abstract

The ancient reductive acetyl-CoA pathway is employed by acetogenic bacteria to form acetate from inorganic energy sources. Since the central pathway does not gain net ATP by substrate-level phosphorylation, chemolithoautotrophic growth relies on the additional formation of ATP via a chemiosmotic mechanism. Genome analyses indicated that some acetogens only have an energy-converting, ion-translocating hydrogenase (Ech) as a potential respiratory enzyme. Although the Ech-encoding genes are widely distributed in nature, the proposed function of Ech as an ion-translocating chemiosmotic coupling site has neither been demonstrated in bacteria nor has it been demonstrated that it can be the only energetic coupling sites in microorganisms that depend on a chemiosmotic mechanism for energy conservation. Here, we show that the Ech complex of the thermophilic acetogenic bacteriumThermoanaerobacter kivuiis indeed a respiratory enzyme. Experiments with resting cells prepared fromT. kivuicultures grown on carbon monoxide (CO) revealed CO oxidation coupled to H2formation and the generation of a transmembrane electrochemical ion gradient (Δµ∼ion). Inverted membrane vesicles (IMVs) prepared from CO-grown cells also produced H2and ATP from CO (via a loosely attached CO dehydrogenase) or a chemical reductant. Finally, we show that Ech activity led to the translocation of both H+and Na+across the membrane of the IMVs. The H+gradient was then used by the ATP synthase for energy conservation. These data demonstrate that the energy-converting hydrogenase in concert with an ATP synthase may be the simplest form of respiration; it combines carbon dioxide fixation with the synthesis of ATP in an ancient pathway.

Whole-cell biocatalysis for hydrogen storage and syngas conversion to formate using a thermophilic acetogen

“…However, A. woodii cannot grow on syngas or CO [20,21] and resting cells produced only little formate from syngas and high amounts of acetate were still produced as unwanted side product [14]. In contrast, the HDCR containing thermophile T. kivui can grow in mineral medium on CO or syngas [22,23]. Therefore, we started out to analyze hydrogenation of CO 2 in a whole-cell system of T. kivui with the aim to increase productivity (due to its thermophilic nature) and to establish an efficient whole-cell biocatalyst for hydrogen storage and formate production from syngas.…”

Carbon monoxide-dependent transcriptional changes in a thermophilic, carbon monoxide-utilizing, hydrogen-evolving bacterium Calderihabitans maritimus KKC1 revealed by transcriptomic analysis

“…Moreover, cooS expression is upregulated in the presence of CO, despite the fact that no sequence motif is recognized by the CO-responsive transcriptional activator CooA in C. pertinax (Fukuyama et al 2018(Fukuyama et al , 2019a. Similarly, ech expression is upregulated in the presence of CO, although the genome does not encode any previously described COresponsive transcription factors in T. kivui (Schoelmerich and Müller 2019). These studies suggest that there are previously unknown transcriptional response mechanisms to CO.…”

“…2; Tables 1 and S2). All of the genes in the cooS2-ech1 (cootype) gene cluster (KKC1_RS06640-KKC1_RS06680) were upregulated DEGs in the presence of CO, indicating that the Ni-CODH/ECH (Coo-type) complex was responsible for CO-dependent H 2 production, similar to other hydrogenogenic carboxydotrophs (Soboh et al 2002;Singer et al 2006;Schut et al 2016;Schoelmerich and Müller 2019). Conversely, the expression level of the ech2 (hyc/hyf-type) gene cluster (KKC1_RS01155-KKC1_RS01200) was unchanged under CO conditions, indicating a potential function with its gene neighbor encoding the putative formate dehydrogenase.…”

“…Hydrogenogenic carboxydotrophs couple CO oxidation with proton reduction to produce hydrogen (H 2 ), during which the proton-or sodium-motive force is generated with residual energy via a Ni-CODH/energy converting hydrogenase (ECH) complex (Singer et al 2006;Schut et al 2016;Schoelmerich and Müller 2019). CO-dependent H 2 production by hydrogenogenic carboxydotrophs is considered a "safety valve" to reduce toxic CO and supply H 2 , which is an energy source for H 2 -utilizing microbial communities (Techtmann et al 2009).…”

“…The functions of these cooS genes have been predicted from their genomic contexts such as ECH, WLP, and ferredoxin-NAD(P)H oxidoreductase (Techtmann et al 2012;Inoue et al 2019), which are presumed to be regulated by CO-responsive transcription factors, such as CooA and RcoM (Shelver et al 1995;Komori et al 2007;Kerby et al 2008). However, recent studies of two hydrogenogenic carboxydotrophs, Carboxydothermus pertinax and Thermoanaerobacter kivui, show that the enzymatic coupling of cooS and ech genes that are distantly encoded in their respective genomes enables CO-dependent H 2 production (Fukuyama et al 2018(Fukuyama et al , 2019aSchoelmerich and Müller 2019). Moreover, cooS expression is upregulated in the presence of CO, despite the fact that no sequence motif is recognized by the CO-responsive transcriptional activator CooA in C. pertinax (Fukuyama et al 2018(Fukuyama et al , 2019a.…”