amoA

AmoA is the gene encoding the alpha subunit of ammonia monooxygenase, the enzyme that catalyzes the oxidation of ammonia to hydroxylamine, the first and rate-limiting step in aerobic nitrification. The enzyme is a membrane-associated copper-containing monooxygenase functioning as part of a multi-subunit complex that includes AmoB and AmoC. In bacteria, amoA is typically located in an operon with amoB and amoC (the amoCAB cluster). In ammonia-oxidizing archaea (AOA), the archaeal amoA gene encodes the equivalent subunit and represents a distinct lineage within the Thaumarchaeota.

Ammonia oxidation is carried out by two major groups of microorganisms: ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA). AmoA sequences are widely used as molecular markers to study these communities because they are directly linked to the key functional step of nitrification. Primer sets targeting bacterial or archaeal amoA, together with PCR, quantitative PCR, amplicon sequencing, and metagenomic approaches, enable assessments of abundance, diversity, and potential activity in soils, freshwater, and marine environments.

Ecologically, ammonia oxidation links nitrogen mineralization and nitrate production, influencing soil fertility, aquatic nitrogen cycling, and the performance of wastewater treatment systems. Environmental factors such as ammonia availability, oxygen concentration, pH, and temperature shape amoA-bearing communities and nitrification rates. The estudo of amoA continues to illuminate the ecological roles of AOB and AOA across diverse ecosystems.