Comammox Functionality Identified in Diverse Engineered Biological Wastewater Treatment Systems

Area of Science:

• Environmental microbiology
• Wastewater engineering
• Nitrogen cycling

Background:

• Complete ammonia oxidation (comammox) by Nitrospira-lineage bacteria (CMX) is a significant nitrogen transformation pathway.
• CMX contributes to nitrogen cycling in engineered biological nitrogen removal (BNR) processes alongside ammonia-oxidizing bacteria (AOB), nitrite-oxidizing bacteria (NOB), and anaerobic ammonia-oxidizing (anammox) bacteria (AMX).

Purpose of the Study:

• To quantify the presence and elucidate the potential functionality of CMX in full-scale BNR systems.
• To assess the contribution of CMX to nitrogen cycling in diverse wastewater treatment configurations.

Main Methods:

• Conducted a metagenomic survey of 16 full-scale BNR configurations.
• Utilized an expanded database combining CMX genomes with published AOB, NOB, and AMX genomes for metagenomic read alignment.
• Performed phylogenetic analysis of key nitrification functional genes (amoA, haoB, nxrB).

Main Results:

• CMX-assigned metagenomic reads ranged from 0.28 to 0.64% of total coding DNA sequences across all BNR configurations.
• Phylogenetic analysis confirmed the presence of CMX-specific coding regions for key nitrification enzymes in all systems.
• Demonstrated the ubiquitous presence and metabolic functionality of CMX bacteria in diverse BNR systems.

Conclusions:

• CMX bacteria are ubiquitously present and metabolically functional in full-scale BNR systems.
• The findings emphasize the need to integrate novel bacterial transformations, like comammox, into the interrogation, operation, and design of engineered biological processes for enhanced nitrogen removal.