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 CO2. 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 anaerobic digesters 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 anaerobic digester microbiota. We also identify core and conditionally rare or abundant taxa, encompassing less than 1000 genera and species. These represent 83-99% and 10-64% 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 AD process. Our online global MiDAS Field Guide presents the data generated in this study and summarizes present knowledge about all taxa.