Underpinning unique genes in Ca. Brocadia sp. and its interspecies association potentials in a partial nitrification/anammox system with low-strength wastewater

Anaerobic ammonia oxidation (anammox) incorporated with anaerobic treatment with sewage offers an energy-efficient option. With the substrate in scare from anaerobically-treated sewage, the dominated anammox species, their mechanisms, and interspecies interaction remain unclear. Here, we enriched and operated a partial nitrification (PN)- anammox (A) fluidized-bed bioreactor (FBR) containing granular activated carbon (GAC) inoculated from a conventional activated sludge with a synthetic low-strength wastewater under a dissolved oxygen concentration of 0.7 mg/L. It achieved over 53% of total nitrogen removal without anammox seed. Our meta-omics analyses revealed an enriched anammox strain affiliated to Ca. Brocadia sp. with a relative abundance of 11.18% and 26.96% in the bulk and biofilm, respectively. Genes encoding dissimilatory nitrate reduction to ammonium (DNRA) and heterotrophic anabolism in this strain were recovered, suggesting its potential in a flexible nitrogen stochiometric feed ratio through organics utilization. Furthermore, 17 and 19 high-quality draft genomes yielded from the bulk and biofilm, respectively support the interspecies interaction capacity between Ca. Brocadia sp. and other nitrogen cycle microorganisms through nitrite loop and vitamin B12 exchange. By offering such overlooked pathways and their interspecies linkages between Ca. Brocadia sp. and other microbes, our study facilitates its mainstream application.