MiDAS 5: Global diversity of bacteria and archaea in anaerobic digesters

Anaerobic digestion represents a key biotechnology for the transformation of organic waste into renewable energy (biogas) and relies on complex microbial communities that work in concert to degrade the complex substrates into methane and carbon dioxide. Here, we sequenced more than half a million high-quality, full-length 16S rRNA gene sequences from 285 full-scale anaerobic digesters (ADs) across the world to expand our knowledge about diversity and function of the bacteria and archaea in ADs. The sequences were processed into full-length 16S rRNA amplicon sequence variants (FL-ASVs), which were added to the MiDAS 4 database for bacteria and archaea in wastewater treatment systems to create MiDAS 5. The expansion of the MiDAS database significantly increased the coverage for bacteria and archaea in ADs worldwide, leading to an improved rate of genus and species-level classification. Using MiDAS 5, we carried out an amplicon-based, global-scale microbial community profiling of the sampled ADs using three common sets of primers targeting different regions of the 16S rRNA gene in bacteria and/or archaea. We revealed how environmental conditions and biogeography shape the AD microbiota. We also identify core and conditionally rare or abundant taxa, encompassing 692 genera and 1013 species. These represent 84-99% and 18-61% of the accumulated read abundance respectively, across samples depending on the amplicon primers used. Finally, we examined the global diversity of functional groups with known importance for the anaerobic digestion process. Our online global MiDAS Field Guide presents the data generated in this study and summarizes present knowledge about all taxa.