Distribution of ammonia-oxidizing Betaproteobacteria community in surface sediment off the Changjiang River Estuary in summer

The spatial distribution of ammonia-oxidizing Betaproteobacteria (beta AOB) was investigated by FISH (fluorescence in situ hybridization) and DGGE (denaturing gradient gel electrophoresis) techniques in the sediment off the Changjiang River Estuary. Sediment samples were collected from eight stations in June before the formation of hypoxia zone in 2006. The abundance of beta AOB ranged from 1.87 x 10(5) to 3.53 x 10(5) cells/g of sediment. beta AOB abundance did not present a negative correlation with salinity, whereas salinity was implicated as the primary factor affecting nitrification rates. The DGGE profiles of PCR-amplified amoA gene fragments revealed that the beta AOB community structure of sample S2 separated from other samples at the level of 40% similarity. The variations in composition of beta AOB were significantly correlated with the salinity, temperature, absorption ability of sediments and TOC. The statistical analysis indicates that the beta AOB abundance was a main factor to influence nitrification rates with an influence ratio of 87.7% at the level of 40% biodiversity similarity. Considering the good correlation between beta AOB abundance and nitrification estimates, the abundance and diversity of beta AOB community could be expected as an indirect index of nitrification activity at the study sea area in summer.