Feammox Acidimicrobiaceae bacterium A6, a lithoautotrophic electrode-colonizing bacterium

ABSTRACT An Acidimicrobiaceae bacterium A6 (A6), from the Acitnobacteria phylum was recently identified as a microorganism that can carry out anaerobic ammonium oxidation coupled to iron reduction, a process also known as Feammox. Being an iron-reducing bacterium, A6 was studied as a potential electrode-reducing bacterium that may transfer electrons extracellularly onto electrodes while gaining energy from ammonium oxidation. Actinobacteria species have been overlooked as electrogenic bacteria, and the importance of lithoautotrophic iron-reducers as electrode-reducing bacteria at anodes has not been addressed. By installing electrodes in soil of a forested riparian wetland where A6 thrives, as well as in A6 bioaugmented constructed wetland (CW) mesocosms, characteristics and performances of this organism as an electrode-reducing bacterium candidate were investigated. In this study, we show that Acidimicrobiaceae bacterium A6 is a lithoautotrophic bacterium, capable of colonizing electrodes in the field as well as in CW mesocosoms, and that it appears to be an electrode-reducing bacterium since there was a boost in current production shortly after the CWs were seeded with Acidimicrobiaceae bacterium A6. IMPORTANCE Most studies on electrogenic microorganisms have focused on the most abundant heterotrophs, while other microorganisms also commonly present in electrode microbial communities such as Actinobacteria have been overlooked. The novel Acidimicrobiaceae bacterium A6 (Actinobacteria) is an iron-reducing bacterium that can colonize the surface of anodes and is linked to electrical current production, making it an electrode-reducing candidate. Furthermore, A6 can carry out anaerobic ammonium oxidation coupled to iron reduction, therefore, findings from this study open up the possibility of using electrodes instead of iron as electron acceptors as a mean to promote A6 to treat ammonium containing wastewater more efficiently. Altogether, this study expands our knowledge on electrogenic bacteria and opens up the possibility to develop Feammox based technologies coupled to bioelectric systems for the treatment NH 4 + and other contaminants in anoxic systems.