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Primordial microorganisms are postulated to have emerged in H2-rich alkaline Hadean serpentinite-hosted environments with homoacetogenesis as a core metabolism. However, investigation of two modern serpentinization-active analogues of early Earth reveals that conventional H2-/CO2-dependent homoacetogenesis is thermodynamically unfavorable in situ due to picomolar CO2 levels. Through metagenomics and thermodynamics, we discover unique taxa capable of metabolism adapted to the habitat. This included a novel deep-branching phylum, “Ca. Lithoacetigenota”, that exclusively inhabits Hadean analogues and harbors genes encoding alternative modes of H2-utilizing lithotrophy. Rather than CO2, these metabolisms utilize reduced carbon compounds detected in situ presumably serpentinization-derived: formate and glycine. The former employs a partial homoacetogenesis pathway and the latter a distinct pathway mediated by a rare selenoprotein – the glycine reductase. A survey of serpentinite-hosted system microbiomes shows that glycine reductases are diverse and nearly ubiquitous in Hadean analogues. “Ca. Lithoacetigenota” glycine reductases represent a basal lineage, suggesting that catabolic glycine reduction is an ancient bacterial innovation for gaining energy from geogenic H2 even under serpentinization-associated hyperalkaline, CO2-poor conditions. This draws remarkable parallels with ancestral archaeal H2-driven methyl-reducing methanogenesis recently proposed. Unique non-CO2-reducing metabolic strategies presented here may provide a new view into metabolisms that supported primordial life and the diversification of LUCA towards Archaea and Bacteria.

Supplementary informationis available for this paper athttps://doi.org/10.1038/s41467-020-18906-7, Six CO2 fixation pathways are known to operate in photoautotrophic and chemoautotrophic microorganisms. Here, we describe chemolithoautotrophic growth of the sulphate-reducing bacterium Desulfovibrio desulfuricans (strain G11) with hydrogen and sulphate as energy substrates. Genomic, transcriptomic, proteomic and metabolomic analyses reveal that D. desulfuricans assimilates CO2 via the reductive glycine pathway, a seventh CO2 fixation pathway. In this pathway, CO2 is first reduced to formate, which is reduced and condensed with a second CO2 to generate glycine. Glycine is further reduced in D. desulfuricans by glycine reductase to acetyl-P, and then to acetyl-CoA, which is condensed with another CO2 to form pyruvate. Ammonia is involved in the operation of the pathway, which is reflected in the dependence of the autotrophic growth rate on the ammonia concentration. Our study demonstrates microbial autotrophic growth fully supported by this highly ATP-efficient CO2 fixation pathway., We acknowledge Änne-Michaelis and William Newell for assistance with the LC-MS forthe metabolomics experiments and Daniel Amador-Noguez for access to the LC-MS usedfor13C intracellular metabolomic analysis. We thank Ines Cardoso Pereira and John vander Oost for critically reading the manuscript. This research was funded by the Neth-erlands Organisation for Scientific Research (NWO) through SIAM Gravitation Grant024.002.002 and the Innovation Program Microbiology (WUR), NJC acknowledgesfunding from NWO through a Rubicon Grant (019.163LW.035) and a Veni Grant(VI.Veni.192.156)., info:eu-repo/semantics/publishedVersion

International audience; For the human pathogen Clostridioides (also known as Clostridium) difficile, the ability to adapt to nutrient availability is critical for its proliferation and production of toxins during infection. Synthesis of the toxins is regulated by the availability of certain carbon sources, fermentation products and amino acids (e.g. proline, cysteine, isoleucine, leucine and valine). The effect of proline is attributable at least in part to its role as an inducer and substrate of D-proline reductase (PR), a Stickland reaction that regenerates NAD+ from NADH. Many Clostridium spp. use Stickland metabolism (co-fermentation of pairs of amino acids) to generate ATP and NAD+ . Synthesis of PR is activated by PrdR, a proline-responsive regulatory protein. Here we report that PrdR, in the presence of proline, represses other NAD+ -generating pathways, such as the glycine reductase and succinate-acetyl CoA utilization pathways leading to butyrate production, but does so indirectly by affecting the activity of Rex, a global redox-sensing regulator that responds to the NAD+ /NADH ratio. Our results indicate that PR activity is the favored mechanism for NAD+ regeneration and that both Rex and PrdR influence toxin production. Using the hamster model of C. difficile infection, we revealed the importance of PrdR-regulated Stickland metabolism in the virulence of C. difficile.

Studying amino acid catabolism-coupled methanogenesis is the important standpoints to decipher the metabolic behavior of a methanogenic culture. l-Glycine and l-alanine are acted as sole carbon and nitrogen sources for acidogenic bacteria. One amino acid is oxidized and another one is reduced for acetate production via pyruvate by oxidative deamination process in the Stickland reactions. Herein, we have developed a kinetic model for the Stickland reactions-coupled methanogenesis (SRCM) and simulated objectively to maximize the rate of methane production. We collected the metabolic information from enzyme kinetic parameters for amino acid catabolism of Clostridium acetobutylicum ATCC 824 and methanogenesis of Methanosarcina acetivorans C2A. The SRCM model of this study consisted of 18 reactions and 61 metabolites with enzyme kinetic parameters derived experimental data. The internal or external metabolic flux rate of this system found to control the acidogenesis and methanogenesis in a methanogenic culture. Using the SRCM model, flux distributions were calculated for each reaction and metabolite in order to maximize the methane production rate from the glycine–alanine pair. Results of this study, we demonstrated the metabolic behavior, metabolite pairing while mutually interact, and advantages of syntrophic metabolism of amino acid-directed methane production in a methanogenic starter culture. Electronic supplementary material The online version of this article (10.1186/s13568-019-0803-8) contains supplementary material, which is available to authorized users.

Here, we report the draft genome sequence of Gottschalkia purinilyticum (formerly Clostridium purinilyticum ) WA1, an anaerobic bacterium specialized on degradation of purines (including adenine) and glycine, which uses the selenoprotein glycine reductase for substrate degradation. The genome consists of a single chromosome (3.40 Mb).

Here, we report the draft genome sequence of Clostridium cylindrosporum HC-1, a purine- and glycine-fermenting anaerobe, which uses selenoprotein glycine reductase for substrate degradation. The genome consists of a single chromosome (2.72 Mb) and a circular plasmid (14.4 kb).