Isolation from oil reservoirs of novel thermophilic anaerobes phylogenetically related to Thermoanaerobacter subterraneus: reassignment of T. subterraneus, Thermoanaerobacter yonseiensis, Thermoanaerobacter tengcongensis and Carboxydibrachium pacificum to Caldanaerobacter subterraneus gen. nov., sp. nov., comb. nov. as four novel subspecies.

Novel thermophilic, anaerobic, Gram-positive, rod-shaped bacteria, strains SL9 and OCA1, were isolated from oilfields in France and Australia, respectively. Both strains, together with Thermoanaerobacter yonseiensis KB-1(T) (=DSM 13777(T)), Thermoanaerobacter tengcongensis MB4(T) (=DSM 15242(T)) and Carboxydibrachium pacificum JM(T) (=DSM 12653(T)), possessed genomic (DNA-DNA hybridization studies) and phylogenetic similarities with Thermoanaerobacter subterraneus SEBR 7858(T) (=DSM 13054(T)), which was isolated recently from an oilfield reservoir in south-west France. Marked phenotypic differences exist between the three oilfield isolates (T. subterraneus, strain OCA1 and strain SL9): they include temperature range for growth and substrates used. Differences were also observed in the DNA G+C contents of all organisms. Similarly to T. subterraneus, strains SL9 and OCA1, and also T. yonseiensis, T. tengcongensis and Carboxydibrachium pacificum, produced acetate and L-alanine as major end products of glucose metabolism [0.8-1.0 mol L-alanine produced (mol glucose consumed)(-1)] and reduced thiosulfate, but not sulfate, to sulfide. Because of these significant metabolic and phylogenetic differences between the oilfield isolates (T. subterraneus, strain OCA1 and strain SL9), T. yonseiensis, T. tengcongensis and Carboxydibrachium pacificum and other Thermoanaerobacter species, it is proposed to reassign them as a novel genus and species, Caldanaerobacter subterraneus gen. nov., sp. nov., comb. nov., with the creation of four novel subspecies, Caldanaerobacter subterraneus subsp. subterraneus subsp. nov., comb. nov., Caldanaerobacter subterraneus subsp. yonseiensis subsp. nov., comb. nov., Caldanaerobacter subterraneus subsp. tengcongensis subsp. nov., comb. nov. and Caldanaerobacter subterraneus subsp. pacificus subsp. nov., comb. nov.