Insights into the phylogenetic and metabolic diversity of <i>Planctomycetota</i> in anaerobic digesters and the isolation of novel <i>Thermoguttaceae</i> species

Studying bacteria in anaerobic digestion (AD) is crucial for optimizing microbial processes. While abundant taxa are often studied, less abundant groups may harbour novel metabolic potential. This study fills the gap by focusing on the Planctomycetota phylum, known to encode diverse carbohydrate-active enzymes (CAZymes). Despite their common presence in diverse aerobic and anaerobic environments, their role in AD is relatively unexplored. We utilized both culture-dependent and culture-independent techniques to investigate the phylogenetic and metabolic diversity of Planctomycetota within AD reactors. Our findings revealed that among the diverse planctomycetotal operational taxonomic units present, only a few are prevalent and abundant community members. Planctomycetota share functional traits with e.g. Verrucomicrobiota exhibiting distinct CAZyme gene repertoires that indicates specialization in degrading algal polysaccharides and glycoproteins. To explore the planctomycetotal metabolic capabilities, we monitored their presence in algal-fed digesters. Additionally, we isolated a strain from mucin-based medium, revealing its genetic potential for a mixotrophic lifestyle. Based on the genomic analysis, we propose to introduce the Candidatus Luxemburgiella decessa gen. nov. sp. nov., belonging to the Thermoguttaceae family within the Pirellulales order of the Planctomycetia class. This study enhances our understanding of Planctomycetota in AD by highlighting their phylogenetic diversity and metabolic capabilities.