| Abstract |
Four anaerobic syntrophic acetate-oxidizing bacteria, the thermotolerant strains Re1(T), Re2, T1 and T2, were isolated from two different mesophilic methanogenic systems. The strains originate from sludge of a continuously stirred laboratory-scale reactor containing high levels of ammonium and from a high ammonium enrichment culture. Comparative 16S rRNA gene sequence analysis confirmed that the strains belong to the Firmicutes-Clostridia class. The most closely related species to strains Re1(T), Re2, T1 and T2 was Tepidanaerobacter syntrophicus, with a 16S rRNA gene sequence identity of 96%. The DNA-DNA relatedness of strains Re2, T1 and T2 to strain Re1(T) was 92, 102, 81%, respectively. The gene encoding the acetogen key enzyme formyltetrahydrofolate synthetase (FTHFS) was detected and partly sequenced from the strains. In pure culture the bacteria used different organic compounds as carbon and energy source, such as organic acids, alcohols, sugars and amino acids. Furthermore, acetate-oxidizing ability was observed during co-cultivation with a hydrogen-consuming Methanoculleus sp. The bacteria were found to be spore-forming, rod-shaped and motile, and possessed Gram-positive cell walls. The four strains were thermotolerant and grew at temperatures between 25 and 55°C. Strain Re1(T) had a DNA G+C content of 38.4% and the major fatty acids were C(18:1) w7c, C(18:1) w9c, anteiso-C(17:0), C(16:1) w7c and C(18:0). The genetic and phenotypic properties of strains Re1(T), Re2, T1 and T2 suggest classification as representatives of a novel species of the genus Tepidanaerobacter; the name Tepidanaerobacter acetatoxydans sp. nov. is suggested. The type strain of T. acetatoxydans is Re1(T) (=DSM 21804(T)=JCM 16047(T)).
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