THERMOTHRIX AZORENSIS SP-NOV, AN OBLIGATELY CHEMOLITHOAUTOTROPHIC, SULFUR-OXIDIZING, THERMOPHILIC BACTERIUM

A new aerobic, obligately chemolithoautotrophic, thermophilic, sulfur- oxidizing bacterium, Thermothrix azorensis, was isolated from a hot sp ring on Sao Miguel Island in the Azores. The cells of this organism ar e gram negative, nonsporulating, and rod shaped. Filament formation ap pears to occur as a response to nonoptimal growth conditions. Growth o ccurs at 63 to 86 degrees C, and the optimum temperature is 76 to 78 d egrees C. The optimum pH range for growth is 7.0 to 7.5. The G+C conte nt of the DNA of our isolate is 39.7 mol%. This isolate uses thiosulfa te, tetrathionate, hydrogen sulfide, and elemental sulfur as energy so urces, Of particular interest are the absence of Calvin cycle enzymes and the initial appearance of sulfide during the lag phase of growth o f aerobic cultures grown on elemental sulfur. The subsequent formation of thiosulfate is followed by oxidation of the thiosulfate to sulfate . T. azorensis differs from the only other Thermothrix species that ha s been described, Thermothrix thiopara, by having higher optimum and m aximum growth temperatures, by being an obligate chemolithoautotroph, and by its close but separate position on a 16S rRNA sequence-based ph ylogenetic tree. Our T. azorensis isolate has been deposited in the Am erican Type Culture Collection as strain ATCC 51754(T) (T = type strai n).