Whole-Community Metagenomics in Two Different Anammox Configurations: Process Performance and Community Structure.

Anaerobic ammonia oxidation (anammox) combined with partial nitritation (PN) is an innovative treatment process for energy-efficient nitrogen removal from wastewater. In this study, we used genome-based metagenomics to investigate the overall community structure and anammox species enriched in suspended growth (SGR) and attached growth packed-bed (AGR) anammox reactors after 220 days of operation. Both reactors removed more than 85% of the total inorganic nitrogen. Metagenomic binning and phylogenetic analysis revealed that two anammox population genomes, affiliated with the genus Candidatus Brocadia, were differentially abundant between the SGR and AGR. Both of the genomes shared an average nucleotide identify of 83%, suggesting the presence of two different species enriched in both of the reactors. Metabolic reconstruction of both population genomes revealed key aspects of their metabolism in comparison to known anammox species. The community composition of both the reactors was also investigated to identify the presence of flanking community members. Metagenomics and 16S rRNA gene amplicon sequencing revealed the dominant flanking community members in both reactors were affiliated with the phyla Anaerolinea, Ignavibacteria, and Proteobacteria. Findings from this research adds two new species, Ca. Brocadia sp. 1 and Ca. Brocadia sp. 2, to the genus Ca. Brocadia and sheds light on their metabolism in engineered ecosystems.