Hydrogenimesophilus fermentans gen. nov., sp. nov., a novel anaerobic hydrogen-producing bacterium isolated from lacustrine sediment.

Anaerobic lake sediments harbour fermentative micro-organisms that contribute to organic-matter degradation and dihydrogen (H2) turnover. Strain PP1C4T was isolated from sediment of Lake Pavin, a permanently stratified meromictic lake characterized by active anaerobic microbial processes, including methanogenesis and characterized using a polyphasic taxonomic approach. Cells were strictly anaerobic, Gram-stain-negative, motile rods. Growth occurred at 19-37 °C (optimum, 30 °C), pH 7.0-9.0 (optimum, pH 7.0) and NaCl concentrations of 0-20 g l⁻¹ (optimum, 1 g l-1). Glucose fermentation produced propionate and butyrate as major organic end-products together with CO₂ and H2. Phylogenetic analysis placed PP1C4T within the family Oscillospiraceae, with the highest 16S rRNA gene sequence similarity to 'Marasmitruncus massiliensis' Marseille-P3646 (95.2%). The genome was ∼3.4 Mb with a DNA G+C content of 45.6 mol%. Maximum blast-based average nucleotide identity and average amino acid identity values between PP1C4T and the compared taxa were 71.53 and 69.30%, respectively, and in silico DNA-DNA hybridization values ranged from 18.0 to 24.3%. Based on the combined phylogenetic, genomic, phenotypic and chemotaxonomic evidence, strain PP1C4ᵀ represents a novel genus and species within the family Oscillospiraceae, for which the name Hydrogenimesophilus fermentans gen. nov., sp. nov. is proposed. The type strain is PP1C4T (=DSM 118145T=CIP 112512ᵀ).