Importance of Defluviitalea raffinosedens for hydrolytic biomass degradation in co-culture with Hungateiclostridium thermocellum
The bacterial hydrolysis of polysaccharides is an important step for the production of sustainable energy, for example during the conversion of plant biomass to methane-rich biogas. Previously, Hungateiclostridium thermocellum was identified as cellulolytic key player in thermophilic biogas microbiomes. The aim of this study was to physiologically characterize a recently isolated co-culture of Hc. thermocellum and the saccharolytic bacterium Defluviitalea raffinosedens from a laboratory-scale biogas fermenter. The characterization focused on cellulose breakdown by applying the measurement of cellulose hydrolysis, production of metabolites and the activity of secreted enzymes. The substrate degradation as well as the production of volatile metabolites was considerably enhanced when both organisms acted synergistically. To enable the analysis of the genetic basis of its physiological properties, the genome of the D. raffinosedens was sequenced for the first time, resulting in 3,092,142 bp draft genome with 35.67 mol% GC. Further, 16S rRNA amplicon sequencing of lab-scale biogas fermenters at different process conditions was performed. Defluviitalea species were detected in the metagenome and metatranscriptome of thermophilically (50 °C) operated fermenters and were highest (1.44%) in the cDNA of fermenter T2 operating as highly efficient process, supporting the importance of this genus for the hydrolysis of the raw substrate.