Reclassification of Thermoterrabacterium ferrireducens as Carboxydothermus ferrireducens comb. nov., and emended description of the genus Carboxydothermus.

Similarities in phylogeny and metabolic properties between the type species of two monospecific genera of thermophilic anaerobic bacteria, Carboxydothermus hydrogenoformans and Thermoterrabacterium ferrireducens, and analysis of their recently available 16S rRNA gene sequences warranted clarification of their taxonomic positions. We have determined that the value of DNA-DNA hybridization between the type strains is 53 %. Additional physiological studies revealed that C. hydrogenoformans Z-2901(T) is capable of Fe(III) reduction with H(2) as an electron donor and ferrihydrite as an electron acceptor. T. ferrireducens JW/AS-Y7(T) is able to grow and utilize CO with ferrihydrite as an electron acceptor without hydrogen or acetate production. We therefore reclassify Thermoterrabacterium ferrireducens as Carboxydothermus ferrireducens comb. nov. (type strain JW/AS-Y7(T)=DSM 11255(T)=VKM B-2392(T)). The description of the genus Carboxydothermus is emended to include such important physiological properties as growth on organic compounds and capacity for Fe(III) reduction.