Carboxydothermus pertinax sp. nov., a thermophilic, hydrogenogenic, Fe(III)-reducing, sulfur-reducing carboxydotrophic bacterium from an acidic hot spring

Abstract

A novel anaerobic, Fe(III)-reducing, hydrogenogenic, carboxydotrophic bacterium, designated strain Ug1T, was isolated from a volcanic acidic hot spring in southern Kyushu Island, Japan. Cells of the isolate were rod-shaped (1.0–3.0 µm long) and motile due to peritrichous flagella. Strain Ug1Tgrew chemolithoautotrophically on CO (100 % in the gas phase) with reduction of ferric citrate, amorphous iron (III) oxide, 9,10-anthraquinone 2,6-disulfonate, thiosulfate or elemental sulfur. No carboxydotrophic growth occurred with sulfate, sulfite, nitrate or fumarate as electron acceptor. During growth on CO, H2and CO2were produced. Growth occurred on molecular hydrogen as an energy source and carbon dioxide as a sole carbon source. Growth was observed on various organic compounds under an N2atmosphere with the reduction of ferric iron. The temperature range for carboxydotrophic growth was 50–70 °C, with an optimum at 65 °C. The pH25 °Crange for growth was 4.6–8.6, with an optimum between 6.0 and 6.5. The doubling time under optimum conditions using CO with ferric citrate was 1.5 h. The DNA G+C content was 42.2 mol%. Analysis of 16S rRNA gene sequences demonstrated that this strain belongs to the thermophilic carboxydotrophic bacterial genusCarboxydothermus, with sequence similarities of 94.1–96.6 % to members of this genus. The isolate can be distinguished from other members of the genusCarboxydothermusby its ability to grow with elemental sulfur or thiosulfate coupled to CO oxidation. On the basis of phylogenetic analysis and unique physiological features, the isolate represents a novel species of the genusCarboxydothermusfor which the nameCarboxydothermus pertinaxsp. nov. is proposed; the type strain of the novel species is Ug1T( = DSM 23698T = NBRC 107576T).