Community Dynamics and Activity of Ammonia-Oxidizing Prokaryotes in Intertidal Sediments of the Yangtze Estuary

Diversity, abundance, and activity of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were investigated using the ammonia monooxygenase alpha subunit (amoA) in the intertidal sediments of the Yangtze Estuary. Generally, AOB had a lower diversity of amoA genes than did AOA in this study. Clone library analysis revealed great spatial variations in both AOB and AOA communities along the estuary. The UniFrac distance matrix showed that all the AOB communities and 6 out of 7 AOA communities in the Yangtze Estuary were statistically indistinguishable between summer and winter. The studied AOB and AOA community structures were observed to correlate with environmental parameters, of which salinity, pH, ammonium, total phosphorus, and organic carbon had significant correlations with the composition and distribution of both communities. Also, the AOA communities were significantly correlated with sediment clay content. Quantitative PCR (qPCR) results indicated that the abundance of AOB amoA genes was greater than that of AOA amoA genes in 10 of the 14 samples analyzed in this study. Potential nitrification rates were significantly greater in summer than in winter and had a significant negative correlation with salinity. In addition, potential nitrification rates were correlated strongly only with archaeal amoA gene abundance and not with bacterial amoA gene abundance. However, no significant differences were observed between rates measured with and without ampicillin (AOB inhibitor). These results implied that archaea might play a more important role in mediating the oxidation of ammonia to nitrite in the Yangtze estuarine sediments.