Presence and functional potential of comammox in full-scale wastewater treatment systems across the globe

Complete ammonia oxidation (comammox) to nitrate in certain Nitrospira-lineage bacteria (CMX) impede engineered biological nitrogen removal (BNR) processes due to competition with the desired ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and/or anaerobic ammonia oxidizing (anammox) bacteria (AMX). A global metagenomic survey was conducted to explore the presence and potential functionality of CMX in sixteen full-scale BNR configurations. Coding regions from the three published CMX genomes were used to create an expanded database of protein sequences for read alignment. Despite high variability in overall microbial ecology, CMX species consistently accounted for between 0.28 and 0.64% of total coding DNA sequences (CDS). Both the relative contribution to overall functional capacity and the presence of key functional genes supported the theorized advantage of CMX over NOB, yet not AOB, in biofilms through prioritization of growth yield over rate. Ultimately, the ubiquitous presence of CMX bacteria and metabolic functionality in such diverse systems emphasizes the need to translate novel bacterial transformations to engineered biological process design.