Anaerobic ammonium oxidation (anammox) bacteria contribute significantly to the global nitrogen cycle and play a major role in sustainable wastewater treatment. Anammox bacteria convert ammonium (NH4 +) to dinitrogen gas (N2) using intracellular electron acceptors such as nitrite (NO2 −) or nitric oxide (NO). However, it is still unknown whether anammox bacteria have extracellular electron transfer (EET) capability with transfer of electrons to insoluble extracellular electron acceptors. Here we show that freshwater and marine anammox bacteria couple the oxidation of NH4 + with transfer of electrons to insoluble extracellular electron acceptors such as graphene oxide or electrodes in microbial electrolysis cells. 15N-labeling experiments revealed that NH4 + was oxidized to N2 via hydroxylamine (NH2OH) as intermediate, and comparative transcriptomics analysis revealed an alternative pathway for NH4 + oxidation with electrode as electron acceptor. Complete NH4 + oxidation to N2 without accumulation of NO2 − and NO3 − was achieved in EET-dependent anammox. These findings are promising in the context of implementing EET-dependent anammox process for energy-efficient treatment of nitrogen.
Bibliographical noteFunding Information:
This work was supported by Center Competitive Funding Program (FCC/1/1971-33-01) to P.E.S. from King Abdullah University of Science and Technology (KAUST). M.S.M.J. was supported by ERC AG 232937 and 339880 and SIAM OCW/NWO 024002002.
© 2020, The Author(s).
- Ammonium Compounds/metabolism
- Electron Transport
- Extracellular Space/metabolism
- Time Factors
PubMed: MeSH publication types
- Research Support, Non-U.S. Gov't
- Journal Article