Bacterial Community Characteristics and Detection of Denitrifying Functional Genes nirS, nirk in the Coastal Water of Bohai Bay, China Bacterial and denitrifying functional genes in Bohai

To understand the microbial community characteristics and denitrification status in coastal water ecosystem of Bohai Bay, China, the bacterioplankton from six representative stations were collected in September 2016, and the bacterial community and abundance of nir-encoding denitrifying bacteria were studied by 454-pyrosequencing and real-time quantitative PCR (qPCR), respectively. The results showed that the Shannon index of the bacterial community ranged from 4.86 to 5.56. The bacterial composition and their relative abundance varied significantly among the bacterial libraries from the six water samples. Proteobacteria was the largest phylum in the six samples varying between 63.19% and 77.34%. α-proteobacteria was the most abundant class in the W4 station with 46.09%, while γ-proteobacteria was the most abundant class in other five stations ranging from 36.39% to 60.58%. The qPCR results showed that the nirS gene abundance ranged from 2.26×107 copies/L to 9.63×107 copies/L, while nirK gene ranged from 1.01×106 copies/L to 2.09×107 copies/L, indicating that both of them played important roles during the denitrification of the local coastal water. Furthermore, the nirS abundance in each station was significantly higher than that of nirK, suggesting that the functional genes nirS played more important role than nirK in reduction process of nitrite (NO2-) to nitric oxide (NO). Canonical correspondence analysis (CCA) results indicated that petroleum, arsenic (As), chromium (Cr), lead (Pb) and cadmium (Cd) had significant effects on the distribution of bacterial community. In contrast, the key factors regulating the nirS and nirK gene abundances included nitrate (NO3-N), phosphate (PO3-P), chlorophyll a (Chla), As and Cd. Keywords—Bohai Sea; bacteria; denitrification; pyrosequencing; real-time quantitative PCR (qPCR)