Archaeal ammonium oxidation coupled with bacterial nitrite oxidation in a simulated drinking water premise plumbing system

Simulated copper and PVC premise plumbing reactors modeling chloramine decay were monitored for complete nitrification of 0.71 mg NH4-N L-1 ammonium to nitrate with no nitrite detected. PCR, qPCR, fluorescent in situ hybridization (FISH) and DNA sequencing were used to investigate the microbial community responsible for nitrification in the reactors' influent and biofilm on copper and PVC surfaces. No bacterial ammonium oxidizers were detected by directly targeting the bacterial amoA gene or 16S rRNA gene amplicons. FISH images indicated an archaeal population on both surfaces. Archaeal 16S rRNA and amoA gene sequences showed 98.6% and 87.6% similarity to the known archaeal ammonium oxidizer, Candidatus Nitrosotenuis uzonenis. Copy numbers of the archaeal 16S rRNA gene and archaeal amoA approximated a 1 : 1 ratio, suggesting that any archaea in the systems are likely to be ammonium oxidizers. Further, there was evidence for the presence of bacterial nitrite oxidizers. Copper surfaces supported fewer archaea as detected using the archaeal 16S rRNA and amoA genes. The results provide strong evidence for biofilms in a drinking water premise plumbing system composed of archaeal ammonium oxidizers and bacterial nitrite oxidizers, capable of complete oxidation of ammonium to nitrate. Since no bacterial ammonium oxidizers were found, this study adds to the growing body of research indicating an important role for archaeal ammonium oxidizers in freshwater/drinking water environments in the conversion of ammonium to nitrite.