Thermicanus aegyptius gen. nov., sp nov., isolated from oxic soil, a fermentative microaerophile that grows commensally with the thermophilic acetogen Moorella thermoacetica

A thermophilic, fermentative microaerophile (ET-5b) and a thermophilic acet ogen (ET-5a) were coisolated from oxic soil obtained from Egypt. The 16S rR NA 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 st rain of M. thermoacetica. For ET-5b, the nearest 16S rRNA gene sequence sim ilarity 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 gra m 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 succi nate supported growth only under oxic conditions. Saccharides yielded succi nate, lactate, ethanol, acetate, formate, and H-2 under anoxic conditions; fermentation products were also formed under oxic conditions. A new genus i s proposed, the type strain being Thermicanus aegyptius ET-5b gen. nov., sp , nov. (DSMZ 12793). M. thermoacetica ET-5a (DSMZ 12797) grew commensally w ith T. aegyptius ET-5b on oligosaccharides via the interspecies transfer of H-2 formate, and lactate. In support of this interaction, uptake hydrogena se and formate dehydrogenase specific activities were fundamentally greater in M. thermoacetica ET-5a than in T. aegyptius ET-5b. These results demons trate that (i) soils subject to high temperatures harbor uncharacterized th ermophilic microaerophiles, (ii) the classic acetogen M. thermoacetica resi des in such soils, and (iii) trophic links between such soil bacteria might contribute to their in situ activities.