Thermoanaerobium brockii gen. nov. and sp. nov., a new chemoorganotrophic,caldoactive, anaerobic bacterium

The isolation of a new anaerobic thermophilic bacterium, Thermoanaerobium brockii, from volcanic features is described. Successful enrichment required a complex medium containing glucose or other fermentable sugars and incubation temperatures of 55–80° C. Strains of T. brockii were gram positive, rods of uneven length that existed singly, in pairs, chains or filaments. Electron micrographs of thin sections of cell revealed a monolayered cell wall and a constrictive or pinching off cell division process. The organism was nonsporeforming, obligately anaerobic and chemoorganotrophic. The optimal temperature for growth was 65–70° C, the maxium was below 85° C and the minimum above 35° C. The doubling time at the optimal temperature for growth was about 1 h. The DNA base composition of three strains of T. brockii varied from 30.0–31.4 mol % guanosine plus cytosine. Fermentable carbohydrates included glucose, sucrose, maltose, lactose, cellobiose and insoluble starch. The fermentation products of cells grown on glucose were ethanol, lactic acid, acetic acid, hydrogen and carbon dioxide. Growth of all strains tested was inhibited by fairly low concentrations of cycloserine, penicillin, streptomycin, tetracycline and chloramphenicol. The possible ecological, evolutionary, and industrial significance, and taxonomic relationships of Thermoanaerobium are discussed.Abbreviations TYEG complex medium containing mineral salts, 0.3% yeast extract, 1.0% tryptone and 0.5% glucose - O.D. optical density - G+C guanosine plus cytosine