Nitritation/anammox reactor Targeted Locus (Loci)

Barcoded amplicon sequencing was used to generate libraries of partial 16S rRNA genes from a reactor designed to treat anaerobically digested swine waste via nitritation/anammox. Quantitative polymerase chain reaction (qPCR) was also performed on key functional genes associated with anammox activity (hzsA) and denitrification (nosZ), and on 16S rRNA genes for the nitrite-oxidizing bacterial (NOB) genera Nitrobacter and Nitrospira. Reactor contents were sieved into nine size fractions with the resulting libraries compared to the initial seed culture and influent waste. The smallest size fraction (< 75 um) differed greatly from the biomass aggregates represented in the other size fractions and accounted for > 90% of the recovered solids. Anammox bacteria were detected only in the biomass aggregates, denitrifiers were detected in all samples, and neither Nitrobacter nor Nitrospira were detected in any sample of reactor biomass. The dominant sequence among the anammox bacteria was related to Candidatus Kuenenia, despite the fact that the seed culture was dominated by sequences related to Candidatus Brocadia. A second member of the Planctomycetes that was classified as a member of the Phycisphaerales was also abundant in the larger reactor aggregates, although the functional significance of this group is unknown. Aerobic ammonium-oxidizing bacteria were not quantified, but their relative abundances were low; no ammonium-oxidizing archaea were detected in any of the sequence libraries. This work demonstrated that anammox bacteria are associated only with relatively large aggregates and NOB can be successfully repressed in an engineered system for nitrogen removal.