Isolation of Cellulose-Degrading Thermoanaerobacterium Strains from Thermophilic Methanogenic Microbial Communities

The cultures assigned to the genus Thermoanaerobacterium according to the partial sequencing of the 16S rRNA gene were isolated on CM3 and GS2 media at 55°С from two laboratory methanogenic thermophilic cellulolytic microbial communities producing biogas from various paper substrates. Cellulolytic activity was shown for three isolates grown on solid and in liquid media with microcrystalline cellulose and filter paper as the only substrates. In order to compare the phylogenetic relations between these isolates and the reference strains of T. thermosaccharolyticum (DSM 571, M0795, and TG57), it was shown that the isolates I2 and I3 belonged to one cluster, whereas the I1 isolate formed a separate branch on the phylogenetic tree. A unique feature of isolate I2 is the formation of an insoluble yellow affinity substance (YAS), which is usually produced by certain anaerobic cellulolytic bacteria, such as Clostridium thermocellum; it is considered a binding component between the cellulase enzyme and its substrate, cellulose. Our results confirmed that cellulolytic T. thermosaccharolyticum strains predominated among cellulose-degrading bacteria within the thermophilic microbial communities converting the paper substrates into biogas. Although the type strain T. thermosaccharolyticum DSM 571 lacks cellulolytic capacity, our results are consistent with the recent data on the ability of several T. thermosaccharolyticum strains to degrade cellulose.