PUB - Publikationen an der Universität Bielefeld

Biogas is an important renewable energy source in Germany. However, in the course of the German energy transition and for political and economic reasons, biogas plants must become more flexible with regard to varying residue-based substrates and thus changing process conditions, while ensuring a stable and efficient process. To meet these requirements, a deeper understanding of the complex biogas-producing microbial communities and the role of community members in the anaerobic digestion (AD) process is necessary, under consideration of the prevailing process conditions. Therefore, the aim of this thesis was to comprehensively analyse biogas-producing microbial communities with regard to their adaptations to the process conditions in differently operated large-scale agricultural digesters. For this purpose, three different approaches were applied to unravel certain types of adaptations of the microbial communities within biogas plants.
Firstly, a 16S rRNA gene-based taxonomic profiling of 67 differently operated full-scale biogas digesters from 49 biogas plants revealed three marker microbiome clusters and one group of outliers, which could be explained by the prevailing process conditions of the respective biogas digesters. Moreover, taxa were identified which adapted to specific process conditions and were indicative for these marker microbiomes. In contrast, also resilient taxa were identified, which were process condition independent und thus might support stable process conditions within the analyzed 67 biogas digesters.
Secondly, a deep metagenome- and metaproteome-based analysis of the microbial communities of three differently operated digesters of one biogas plant revealed taxonomic and functional adaptations of the whole microbiome and also the role of ten differentially and four evenly abundant metagenomically assembled genomes (MAGs) in the biogas process. Here, especially MAG 80, assigned as member of the class *Limnochordia*, was highly abundant and active in all three digesters suggesting an important role within the AD process, regardless of the prevailing process conditions. Moreover, for MAG 64, classified as the hydrogenotrophic archaeael species *Methanothermobacter wolfeii*, an important role for thermophilic biogas processes is assumed, as it was abundant under thermophilic process conditions and showed high expression of hydrogenotrophic methanogenesis enzymes.
Finally, detailed genome-based analyses of the archaeal isolate *Methanothermobacter wolfeii* SIV6, in combination with *in situ* metatranscriptomics and metagenomics, revealed specific genome features as potential adaptations of this strain, that could explain its competitiveness under the thermophilic process conditions of the corresponding biogas digester. The high transcription of the hydrogenotrophic methanogenesis pathway of this strain indicated the important role of this organism in the final methanogenesis step of the thermophilic AD process.