Context. Success of the partial nitration/anammox (PNA) process relies on a balance of the microbial guilds of aerobic (AOB) and anaerobic ammonia oxidizing bacteria (AnAOB) as well as the suppression of nitrite oxidizing bacteria (NOB). Heterotrophic bacteria (HB) often constitute a large portion of the community. We have previously reported on the success of intermittent aeration to control the PNA process.
Gap. The effect of intermittent aeration on the composition of the PNA microbiome, and especially the resulting genomes of the dominating AOB, AnAOB and HB are not documented.
Aim. We aimed to (i) sequence the metagenome of a microbiome performing high-rate PNA subject to intermittent aeration (ii) assemble dominant high-quality genomes and (iii) inspect the genomes to infer physiological features and dependencies.
Methods. A lab-scale PNA reactor, operated in SBR mode – was subject to intermittent aeration and sampled over a 6 months period. Shot-gun metagenomes were obtained; metagenome assembled genomes inferred and subject to functional annotation.
Findings. Approx. 80 % of the community metagenome was assigned to 57 high-quality MAGs. The AOB and AnAOB guild each comprised 3 MAGs, while no NOB MAG was recovered. The majority of the metagenome encoded heterotrophic MAGs. MAGs with the capability of NO3- to NO2- reduction and N2O to N2 were abundant, MAGs with incomplete denitrification pathways prevailed. MAGs with genetic potential for NO production (and not consumption) suggested NO exchange in the system, hinting at AnAOB growth on NO (not NO2-) as electron acceptor. In addition, there was a high degree of autotrophy among the MAGs, with only the AnAOB MAGs carrying genes for cobalamin synthesis.
Utilization. This study confirms the efficiency of intermittent aeration as a tool to suppress NOB in PNA systems. An tentative role of HB in recycling oxidized NOx between AOB and AnOB is identified.
