this study, the abundance and sequences of amoA genes of ammonia-oxidizing archaea (AOA) and
bacteria (AOB) were determined in seven wastewater treatment plants (WWTPs) whose ammonium
concentrations in influent and effluent wastewaters varied considerably (5.6–422.3 mgN l1 and 0.2–
29.2 mgN l1, respectively). Quantitative real-time PCR showed that the comparative abundance of
AOA and AOB amoA genes differed among the WWTPs. In all three industrial WWTPs, where the influent
and effluent contained the higher levels of ammonium (36.1–422.3 mgN l1 and 5.3–29.2 mgN l1,
respectively), more than four orders of magnitude higher numbers of AOB amoA genes than AOA amoA
genes arose (with less than the limit of detection of AOA amoA genes). In contrast, significant numbers
of AOA amoA genes occurred in all municipal WWTPs (with ammonium levels in the influent and effluent
of 5.6–11.0 mgN l1 and 0.2–3.0 mgN l1, respectively). Statistical analysis suggested that compared to
other plants’ parameters, the ammonium levels in the plants’ effluent showed correlation with the highest
p value to the abundance of AOA amoA genes.