Anaerobium acetethylicum gen. nov., sp nov., a strictly anaerobic, gluconate-fermenting bacterium isolated from a methanogenic bioreactor

A novel strictly anaerobic, mesophilic bacterium was enriched and isolated with gluconate as sole substrate from a methanogenic sludge collected from a biogas reactor. Cells of strain GluBS11(T) stained Gram-positive and were non-motile, straight rods, measuring 3.0-4.5 x 0.8-1.2 rim. The temperature range for growth was 15-37 degrees C, with optimal growth at 30 degrees C, the pH range was 6.5-8.5, with optimal growth at pH 7, and the generation time under optimal conditions was 60 min. API Rapid 32A reactions were positive for a-galactosidase, a-glucosidase and beta-glucosidase and negative for catalase and oxidase. A broad variety of substrates was utilized, including gluconate, glucose, fructose, maltose, sucrose, lactose, galactose, melezitose, melibiose, mannitol, erythritol, glycerol and aesculin. Products of gluconate fermentation were ethanol, acetate, formate, H-2 and CO2. Neither sulfate nor nitrate served as an electron acceptor. Predominant cellular fatty acids (>10 %) were C-14:0, C-16:0, C-16:1 omega 7c/iso-C-15:0 2-OH and C-18:1 omega 7c. The DNA G+C content of strain GluBS11(T) was 44.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequence data revealed that strain GluBS11(T) is a member of subcluster XIVa within the order Clostridiales. The closest cultured relatives are Clostridium herbivorans (93.1 % similarity to the type strain), Clostridium populeti (93.3 %), Eubacterium uniforme (92.4 %) and Clostridium polysaccharolyticum (91.5 %). Based on this 16S rRNA gene sequence divergence (>6.5 %) as well as on chemotaxonomic and phenotypic differences from these taxa, strain GluBS11(T) is considered to represent a novel genus and species, for which the name Anaerobium acetethylicum gen. nov., sp. nov. is proposed. The type strain of Anaerobium acetethylicum is GluBS11(T) (=LMG 28619(T)=KCTC 15450(T)=DSM 29698(T)).