Nitrogen source influences the interactions of comammox bacteria with aerobic nitrifiers

Abstract

Nitrification is an essential biological process in drinking water and wastewater treatment systems for treating nitrogen pollution. The discovery of comammox <i>Nitrospira</i> and their detection alongside canonical nitrifiers in these engineered ecosystems have made it necessary to understand the environmental conditions that regulate their abundance and activity relative to other better-studied nitrifiers. This study aimed to evaluate two important factors that could potentially influence the behavior of nitrifying bacteria and, therefore, impact nitrification processes. Column reactors fed with either ammonia or urea were systematically monitored to capture changes in nitrogen biotransformation and the nitrifying community as a function of influent nitrogen concentration, nitrogen source, and reactor depth. Our findings show that with increased ammonia availability, comammox <i>Nitrospira</i> decreased in abundance while nitrite oxidizers abundance increased. Yet, in systems with increasing urea availability, comammox <i>Nitrospira</i> abundance and diversity increased without an associated reduction in the abundance of canonical nitrifiers.