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Following publication of the original article, the authors noticed an incorrect affiliation for Christine Stürken and Udo Schumacher. The correct affiliations are as follows: Christine Stürken: Institute of Anatomy and Experimental Morphology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. Udo Schumacher: Institute of Anatomy and Experimental Morphology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany. The affiliations have been correctly published in this correction and the original article has been updated.
The lipidome of the marine hyperthermophilic archaeon Pyrococcus furiosus was studied by means of combined thin-layer chromatography and MALDI-TOF/MS analyses of the total lipid extract. 80–90% of the major polar lipids were represented by archaeol lipids (diethers) and the remaining part by caldarchaeol lipids (tetraethers). The direct analysis of lipids on chromatography plate showed the presence of the diphytanylglycerol analogues of phosphatidylinositol and phosphatidylglycerol, the N-acetylglucosamine-diphytanylglycerol phosphate plus some caldarchaeol lipids different from those previously described. In addition, evidence for the presence of the dimeric ether lipid cardiolipin is reported, suggesting that cardiolipins are ubiquitous in archaea.
The pT-differential inclusive production cross section of the prompt charm-strange meson Ds+ in the rapidity range |y|<0.5 was measured in proton–proton collisions at s=7 TeV at the LHC using the ALICE detector. The analysis was performed on a data sample of 2.98×108 events collected with a minimum-bias trigger. The corresponding integrated luminosity is Lint=4.8 nb−1. Reconstructing the decay Ds+→ϕπ+, with ϕ→K−K+, and its charge conjugate, about 480 Ds± mesons were counted, after selection cuts, in the transverse momentum range 2<pT<12 GeV/c. The results are compared with predictions from models based on perturbative QCD. The ratios of the cross sections of four D meson species (namely D0, D+, D⁎+ and Ds+) were determined both as a function of pT and integrated over pT after extrapolating to full pT range, together with the strangeness suppression factor in charm fragmentation. The obtained values are found to be compatible within uncertainties with those measured by other experiments in e+e−, ep and pp interactions at various centre-of-mass energies.
Background: Molecular hydrogen (H2) is an attractive future energy carrier to replace fossil fuels. Biologically and sustainably produced H2 could contribute significantly to the future energy mix. However, biological H2 production methods are faced with multiple barriers including substrate cost, low production rates, and low yields. The C1 compound formate is a promising substrate for biological H2 production, as it can be produced itself from various sources including electrochemical reduction of CO2 or from synthesis gas. Many microbes that can produce H2 from formate have been isolated; however, in most cases H2 production rates cannot compete with other H2 production methods.
Results: We established a formate-based H2 production method utilizing the acetogenic bacterium Acetobacterium woodii. This organism can use formate as sole energy and carbon source and possesses a novel enzyme complex, the hydrogen-dependent CO2 reductase that catalyzes oxidation of formate to H2 and CO2. Cell suspensions reached specific formate-dependent H2 production rates of 71 mmol g protein −1 h−1 (30.5 mmol g CDW −1 h−1) and maximum volumetric H2 evolution rates of 79 mmol L−1 h−1. Using growing cells in a two-step closed batch fermentation, specific H2 production rates reached 66 mmol g CDW −1 h−1 with a volumetric H2 evolution rate of 7.9 mmol L−1 h−1. Acetate was the major side product that decreased the H2 yield. We demonstrate that inhibition of the energy metabolism by addition of a sodium ionophore is suitable to completely abolish acetate formation. Under these conditions, yields up to 1 mol H2 per mol formate were achieved. The same ionophore can be used in cultures utilizing formate as specific switch from a growing phase to a H2 production phase.
Conclusions: Acetobacterium woodii reached one of the highest formate-dependent specific H2 productivity rates at ambient temperatures reported so far for an organism without genetic modification and converted the substrate exclusively to H2. This makes this organism a very promising candidate for sustainable H2 production and, because of the reversibility of the A. woodii enzyme, also a candidate for reversible H2 storage.
Thermoanaerobacter kivui is an acetogenic model organism that reduces CO2 with electrons derived from H2 or CO, or from organic substrates in the Wood–Ljugdahl pathway (WLP). For the calculation of ATP yields, it is necessary to know the electron carriers involved in coupling of the oxidative and reductive parts of metabolism. Analyses of key catabolic oxidoreductases in cell-free extract (CFE) or with purified enzymes revealed the physiological electron carriers involved. The glyceraldehyde-3-phosphate dehydrogenase (GA3P-DH) assayed in CFE was NAD+-specific, NADP+ was used with less than 4% and ferredoxin (Fd) was not used. The methylene-THF dehydrogenase was NADP+-specific, NAD+ or Fd were not used. A Nfn-type transhydrogenase that catalyzes reduced Fd-dependent reduction of NADP+ with NADH as electron donor was also identified in CFE. The electron carriers used by the potential electron-bifurcating hydrogenase (HydABC) could not be unambiguously determined in CFE for technical reasons. Therefore, the enzyme was produced homologously in T. kivui and purified by affinity chromatography. HydABC contained 33.9 ± 4.5 mol Fe/mol of protein and FMN; it reduced NADP+ but not NAD+. The methylene-THF reductase (MetFV) was also produced homologously in T. kivui and purified by affinity chromatography. MetFV contained 7.2 ± 0.4 mol Fe/mol of protein and FMN; the complex did neither use NADPH nor NADH as reductant but only reduced Fd. In sum, these analysis allowed us to propose a scheme for entire electron flow and bioenergetics in T. kivui.
In times of global warming caused by the extensive use of fossil fuels, the need to capture gaseous carbon compounds is growing bigger. Several groups of microorganisms can fix the greenhouse gas CO2. Out of these, acetogenic bacteria are role models in their ability to reduce CO2 with hydrogen to acetate, which makes acetogens prime candidates for genetic modification towards biotechnological production of value-added compounds from CO2, such as biofuels. However, growth of acetogens on gaseous substrates is strongly energy-limited, and successful metabolic engineering requires a detailed knowledge of the bioenergetics. In 1939, Clostridium aceticum was the first acetogen to be described. A recent genomic study revealed that this organism contains cytochromes and therefore may use a proton gradient in its respiratory chain. We have followed up these studies and will present data that C. aceticum does not use a H+ but a Na+ gradient for ATP synthesis, established by a Na+-Rnf. Experimental data and in silico analyses enabled us to propose the biochemistry and bioenergetics of acetogenesis from H2 + CO2 in C. aceticum.
Acetogenic bacteria are a polyphyletic group of organisms that fix carbon dioxide under anaerobic, non-phototrophic conditions by reduction of two mol of CO2 to acetyl-CoA via the Wood–Ljungdahl pathway. This pathway also allows for lithotrophic growth with H2 as electron donor and this pathway is considered to be one of the oldest, if not the oldest metabolic pathway on Earth for CO2 reduction, since it is coupled to the synthesis of ATP. How ATP is synthesized has been an enigma for decades, but in the last decade two ferredoxin-dependent respiratory chains were discovered. Those respiratory chains comprise of a cytochrome-free, ferredoxin-dependent respiratory enzyme complex, which is either the Rnf or Ech complex. However, it was discovered already 50 years ago that some acetogens contain cytochromes and quinones, but their role had only a shadowy existence. Here, we review the literature on the characterization of cytochromes and quinones in acetogens and present a hypothesis that they may function in electron transport chains in addition to Rnf and Ech.
Energy-conserving dimethyl sulfoxide reduction in the acetogenic bacterium Moorella thermoacetica
(2022)
Moorella thermoacetica is one of the well-studied thermophilic acetogenic bacteria. It grows by oxidation of organic substrates, CO or H2 coupled to CO2 reduction to acetate. Here, we describe that M. thermoacetica can also use dimethyl sulfoxide as terminal electron acceptor. Growth of M. thermoacetica on glucose or H2 + CO2 was stimulated by dimethyl sulfoxide (DMSO). Membranes showed a DMSO reductase activity, that was induced by growing cells in presence of DMSO. The enzyme used reduced anthraquinone-2,6-disulfonate, benzyl- and methyl viologen as electron donor, but not NAD(P)H. Activity was highest at pH 5 and 60°C, the Km for DMSO was 2.4 mM. Potential DMSO reductase subunits were identified by peptide mass fingerprinting; they are encoded in a genomic region that contains three potential dmsA genes, three dmsB genes and one dmsC gene. Transcriptome analysis revealed that two different dmsAB gene clusters were induced in the presence of DMSO. The function of these two and their predicted biochemical features are discussed. In addition, the data are in line with the hypothesis that M. thermoacetica can use DMSO alongside CO2 as electron acceptor and DMSO reduction is catalysed by an energy-conserving, membrane-bound electron transport chain with DMSO as final electron acceptor.