Extracellular electron transfer-dependent anaerobic oxidation of ammonium by anammox bacteria

Abstract

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.

Comparative Genome-Centric Analysis of Freshwater and Marine ANAMMOX Cultures Suggests Functional Redundancy in Nitrogen Removal Processes

“…It was stated that HAO enzyme catalyzes the oxidation of NH 2 OH by only three electrons to NO, then an unknown enzyme involves further oxidation reaction for the conversion of NO to NO − 2 . Also, recently it was demonstrated that anammox bacteria oxidized NH + 4 to dinitrogen gas with NH 2 OH as intermediate of the process while transferring electrons to insoluble extracellular electron acceptors such as graphene oxide or electrodes in microbial electrolysis cells (Shaw et al, 2020). Shaw et al (2020) also suggested a potential HAO enzyme in Ca.…”

“…Also, recently it was demonstrated that anammox bacteria oxidized NH + 4 to dinitrogen gas with NH 2 OH as intermediate of the process while transferring electrons to insoluble extracellular electron acceptors such as graphene oxide or electrodes in microbial electrolysis cells (Shaw et al, 2020). Shaw et al (2020) also suggested a potential HAO enzyme in Ca. Brocadia sinica, an ortholog of the proposed nitrite reductase in Ca.…”

“…However, the potential HAO enzyme of Ca. Brocadia sinica proposed elsewhere (Shaw et al, 2020), should be further investigated as a possible candidate for nitrite reductase.…”

Rapid and highly efficient genomic engineering with a novel iEditing device for programming versatile extracellular electron transfer of electroactive bacteria

“…Electroactive bacteria (EAB) are a unique group of bacteria, which can perform extracellular electron transfer (EET) for anaerobic respiration (Lovley, 2003; Shi et al ., 2016; Logan et al ., 2019). EAB species are ubiquitously distributed across diverse niches and can harness a wide range of terminal electron acceptors (Light et al ., 2018; Costa et al ., 2019; Leu et al ., 2020; Shaw et al ., 2020). They are endowed with the important roles in wastewater treatment and environmental remediation (Rahmani et al ., ), bioenergy harvesting, and geoengineering (Guzman et al ., 2019).…”

Metabolism Control in 3D Printed Living Materials

“…30 However, anaerobic organisms such as acetogens or anammox bacteria do not require oxygen, but instead have evolved to use alternative substrates assimilation and cofactors regeneration strategies to produce energy and biomass, and oxygen impermissible LMs could be applicable for cultivating such microbes. [31][32][33] Despite the advances demonstrating possible processes and products, a better understanding of…”