Nitrate-dependent anaerobic ammonium oxidation

Abstract

Anaerobic ammonium oxidation (anammox) bacteria is generally considered to degrade only nitrite (NO2−) and ammonium (NH4+). However, it is unclear, without additional organic carbon sources (formate, acetate and propionate), whether NO3− can be used by anammox bacteria. Here, we demonstrated that anammox bacteria can grow with NO3− as the sole substrate, and the intracellular carbon source (glycogen) can be decomposed to support the nitrogen metabolism of anammox bacteria. NO3− is reduced to NO2− and NH4+ via the dissimilatory nitrate reduction to ammonium (DNRA) pathway, NO2− and NH4+ are subsequently transformed to N2 via normal anammox process. After incubation with nitrate, the transcription gene of nrfA responsible for NH4+ generated from NO2− was up-regulated with NO3− as the sole substrate, and down-regulated in normal anammox process period. Meanwhile, the metatranscriptional variation of key proteins in tricarboxylic acid (TCA) cycle and glycolysis (Glk) showed the same up-regulated trend. Our work indicated the intracellular DNRA function could enable anammox itself to implement complete total nitrogen removal and enhance the viability of anammox bacteria in different natural ecosystems.