Serine Variant of the Reductive Glycine Pathway of CO Fixation in the Anaerobic Thermophile Parvivirga hydrogeniphila

Parvivirga hydrogeniphila Es71-Z01O1 is a thermophilic bacterium capable of anaerobically growing in the range of 25–70°C (optimum 47–60°C) and pH 6.0–8.5 (optimum 6.8–7.2) and using molecular hydrogen or formate as electron donors and Fe(III) as an acceptor. Genomic analysis revealed the presence of genes for the serine branch of the reductive glycine pathway in the absence of glycine reductase genes. Proteomic studies demonstrated increased expression of other key enzymes of this pathway: formate dehydrogenase, methyltetrahydrofolate cyclohydrolase, glycine cleavage system, and serine hydroxymethyltransferase. The rate of autotrophic carbon fixation was 0.357 fmol C/cell day, which is comparable with the rates of known autotrophic microorganisms. The obtained results indicate the functioning of autotrophic CO assimilation in P. hydrogeniphila, with the serine variant of the reductive glycine pathway being the most probable. The results of the study contribute to the understanding of the metabolic diversity of anaerobic microorganisms and expand knowledge about the distribution of different carbon fixation mechanisms in microorganisms belonging to new phylogenetic groups.