Abstract

The anaerobic ammonium oxidation (anammox)bacteria process is a cost-effective technology applied for nitrogen removal in wastewater treatment plants (WWTP). Anammox bacteria is a group of microorganisms belonging to the Brocadiae class that can oxidize ammonium and reduce nitrite to form dinitrogen gas. However, due to its very slow growth rate and to the fact has not been isolated in pure culture, molecular techniques are widely used to study it. This work aimed to apply genome-centric metagenomics to obtain representative genomes to study the metabolic potential and diversity of the anammox community of two granular sludge anammox reactors. The first reactor was an anammox enriched culture operated with synthetic influent for over six years. The second reactor was operated at mainstream conditions treating real wastewater from a partial nitritation process feed with municipal WW and was inoculated with the biomass from the first reactor. Three metagenomics assembled genomes (MAGs) were obtained with over 90% completeness and less than 5% contaminated. They belong to Brocadiae class, Broc-16, Broc-27 and Broc-45. The phylogenomic analysis was performed based on concatenated alignments of 120 single-copy marker genes and compared with 24 near-completed reference genomes. According to this, Planc-27 bunched with Candidatus (Ca.) Brocadia pituitae and Planc-45 with Ca. Brocadia fulgida. Planc-16 was not directly associated with any previously described species. Thus, a phylogenetic tree based on the 16S rRNA gene was constructed. Planc-16 bunched in the same clade of our recently proposed new specie, Ca. Brocadia barcinensis, dominant in the enriched anammox culture. From the potential metabolic analysis, the functional genes hydrazine synthase and hydrazine dehydrogenase were found. This MAG lacks nitrite reductase genes (nirK and nirS). Nevertheless, the hydroxylamine oxidoreductase gene was found, which could be used as nitrite reductase. In addition, marker genes for dissimilatory nitrate reduction to ammonia were also found.