Isolation and characterization of two new homoacetogenic hydrogen-utilizing bacteria from the human intestinal tract that are closely related to Clostridium coccoides

Two gram-positive, strictly anoxric, coccoid- to rod-shaped strains of bacteria, Clostridium cocroides 1410 acid C. coccoides 3110, were isolated from human feces on the typical homaoacetogenic substrates formate plus H-2 plus CO2 (strain 1410) and vanillate piles H-2 plus CO2 (strain 3110) in the presence of 2-bromoethanesulfonate to inhibit methanogenesis. On the basis of 16S rRNA sequencing, DNA-DNA hybridization, and physiological and morphological parameters, both isolates are closely related to C. coccoides DSM 935(T). The G+C contents of the DNA were 46.1 and 46.2 mol% for C. coccoides 1410 and C. coccoides 3110, respectively. Cytochromes could not be detected, Formate was degraded exclusively to acetate, whereas vanillate was O-demethylated, resulting in acetate and 3,4-dihydroxybenzoate, the latter being further decarboxylated to catechol. In the presence of organic substrates, H-2 was cometabolized to acetate, but both strains failed to grow autotrophically. Lactose, lactulose, sorbitol, glucose, and various other carbohydrates supported growth as well. Untypical of homoacetogens, glucose and sorbitol were fermented not exclusively to acetate; instead, considerable amounts of succinate and D-lactate were produced, H-2 was evolved from carbohydrates only in negligible traces. Acetogenesis from formate plus H-2 plus CO2 or vanillate plus H-2 plus CO2 was constitative, whereas utilization of carbohydrates was inducible, Hydrogenase, CO dehydrogenase, formate dehydrogenase, and all of the tetrahydrofolic acid-dependent, C-1 compound-converting enzymes of the acetyl-coenzyme A pathway of homoacetogenesis were present in cell extracts.