ABSTRACT
A thermophilic, fermentative microaerophile (ET-5b) and a thermophilic acetogen (ET-5a) were coisolated from oxic soil obtained from Egypt. The 16S rRNA gene sequence of ET-5a was 99.8% similar to that of the classic acetogen Moorella thermoacetica. Further analyses confirmed that ET-5a was a new strain of M. thermoacetica. For ET-5b, the nearest 16S rRNA gene sequence similarity value to known genera was approximately 88%. ET-5b was found to be a motile rod with a genomic G+C content of 50.3 mol%. Cells were weakly gram positive and lacked spores. Growth was optimal at 55 to 60 degrees C and pH 6.5 to 7.0. ET-5b grew under both oxic and anoxic conditions, but growth was erratic under atmospheric concentrations of O(2). Utilizable substrates included oligosaccharides and monosaccharides. Acetate, formate, and succinate supported growth only under oxic conditions. Saccharides yielded succinate, lactate, ethanol, acetate, formate, and H(2) under anoxic conditions; fermentation products were also formed under oxic conditions. A new genus is proposed, the type strain being Thermicanus aegyptius ET-5b gen. nov., sp. nov. (DSMZ 12793). M. thermoacetica ET-5a (DSMZ 12797) grew commensally with T. aegyptius ET-5b on oligosaccharides via the interspecies transfer of H(2) formate, and lactate. In support of this interaction, uptake hydrogenase and formate dehydrogenase specific activities were fundamentally greater in M. thermoacetica ET-5a than in T. aegyptius ET-5b. These results demonstrate that (i) soils subject to high temperatures harbor uncharacterized thermophilic microaerophiles, (ii) the classic acetogen M. thermoacetica resides in such soils, and (iii) trophic links between such soil bacteria might contribute to their in situ activities.
