Clostridium thailandense sp. nov., a novel CO2-reducing acetogenic bacterium isolated from peatland soil

Some species of the genus Clostridium are efficient acetate producers and have been deemed useful for upgrading industrial biogas. An acetogenic, strictly anaerobic, Gram-stain-positive, subterminal endospore-forming bacterium designated strain PL3(T) was isolated from peatland soil enrichments with H-2 and CO2. Cells of strain PL3(T) were 0.8-1.0x4.0-10.0 mu m in size and rod-shaped. Growth of strain PL3(T) occurred at pH 6.0-7.5 (optimum, pH 7.0), at 20-40 degrees C (optimum, 30 degrees C) and with 0-1.5 % (w/v) NaCl (optimum, 0.5%). Biochemical analyses revealed that strain PL3(T) metabolized lactose, maltose, raffinose, rhamnose, lactic acid, sorbitol, arabinose and glycerol. Acetic acid was the predominant metabolite under anaerobic respiration with H-2/CO2. The major cellular fatty acids were C-16:0, C-16:1 cis 9 and C-17:0 cyc. The main polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, aminolipid and aminophospholipid. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain PL3(T) belongs to the genus Clostridium with the highest sequence similarity to Clostridium aciditolerans DSM 17425(T) (98.6 %) followed by Clostridium nitrophenolicum (97.8 %). The genomic DNA G+C content of strain PL3(T) was 31.1 mol%.The genomic in silico DNA-DNA hybridization value between strain PL3(T) and C. aciditolerans DSM 17425(T) was 25.1 %, with an average nucleotide identity of 80.2 %. Based on phenotypic, chemotaxonomic and phylogenetic differences, strain PL3(T) was suggested to represent a novel species of the genus Clostridium , for which the name Clostridium thailandense sp. nov. is proposed. The type strain is PL3(T) (=DSM 111812(T)=TISTR 2984(T)).