Electrode colonization by the Feammox bacterium Acidimicrobiaceae sp. strain A6

Acidimicrobiaceae sp. strain A6 (A6), from the Actinobacteria phylum, was recently identified as a microorganism that can carry out anaerobic ammonium (NH ₄ ⁺ ) 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 NH ₄ ⁺ oxidation. Actinobacteria species have been overlooked as electrogenic bacteria, and the importance of lithoautotrophic iron reducers as electrodereducing bacteria at anodes has not been addressed. By installing electrodes in the soil of a forested riparian wetland where A6 thrives, in soil columns in the laboratory, and in A6-bioaugmented constructed wetland (CW) mesocosms and by operating microbial electrolysis cells (MECs) with pure A6 culture, the characteristics and performances of this organism as an electrode-reducing bacterium candidate were investigated. In this study, we show that Acidimicrobiaceae sp. strain A6, a lithoautotrophic bacterium, is capable of colonizing electrodes under controlled conditions. In addition, A6 appears to be an electrode-reducing bacterium, since current production was boosted shortly after the CWs were seeded with enrichment A6 culture and current production was detected in MECs operated with pure A6, with the anode as the sole electron acceptor and NH ₄ ⁺ as the sole electron donor.