Denitrifying bacteria with high abundances in anammox communities play crucial roles in achieving stable anammox-based systems. Despite the relative constant composition of denitrifying bacteria, their functional diversity remains to be explored in anammox communities. Herein, a total of 77 high-quality metagenome-assembled genomes (MAGs) of denitrifying bacteria were recovered from the anammox community in a full-scale swine wastewater treatment plant. Among these microbes, a total of 26 MAGs were affiliated with the seven dominant denitrifying genera that have total abundances higher than 1%. A meta-analysis of these species suggested that external organics reduced the abundances of genus Ignavibacterium and species MAG.305 of UTPRO2 in anammox communities. Comparative genome analysis revealed functional divergence across different denitrifying bacteria, largely owing to their distinct capabilities for carbohydrate (including endogenous and exogenous) utilization and vitamin (e.g., pantothenate and thiamine) biosynthesis. Serval microbes in this system contained fewer genes encoding biotin, pantothenate and methionine biosynthesis compared with their related species from other habitats. In addition, the genes encoding energy production and conversion (73 genes) and inorganic ion transport (53 genes) putatively transferred from other species to denitrifying bacteria, while these denitrifying bacteria (especially genera UTPRO2 and SCN-69-89) likely donated the genes encoding nutrients (e.g., inorganic ion and amino acid) transporter (64 genes) for other members to utilize new metabolites. Collectively, these findings highlighted the functional divergence of these denitrifying bacteria and speculated that the genetic interactions within anammox communities through horizontal gene transfer may be one of the reasons for their functional divergence.
Keywords: Anammox community; Denitrifying bacteria; Functional divergence; Horizontal gene transfer.
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