Ecological linkages and metagenomic analysis reveal partial denitrification of companion bacteria in mixotrophic anammox consortia

Although partial denitrification coupled with the anammox process has received much attention, the partial denitrification of companion bacteria that exists in mixotrophic anammox consortia remains to be experimentally investigated. This study realized the partial denitrification process in mixotrophic anammox consortia with a C/N ratio of 0.75, and the removal efficiency of total nitrogen was 99.0 %. norank_f__Xanthobacteraceae and Denitratisoma were significantly enriched during the whole experiment, which involved mainly companion bacteria with the function of partial denitrification in mixotrophic anammox consortia. Denitratisoma was more likely to convert nitrate or nitrite to nitrogen by cross-feeding with other heterotrophic denitrifying bacteria when the C/N ratio was 1.0. Metagenomic analysis indicated that denitrification genes of nitrate reductase (nap and nar), nitrite reductase (nirS and nirK), nitric oxide reductase (nor), and nitrous oxide reductase (nos) in the mixotrophic anammox increased by 17.15%, 135.40%, -28.00%, and 4.60%, respectively, in contrast to those in the autotrophic anammox. Therefore, nitric oxide might be used as the medium for cross-feeding of partial denitrification and anammox in nitrogen metabolism.