Contrasting diversity pattern of Cytophaga-Flavobacteria in the estuarine and open ocean regions of the East China Sea

Cytophaga-Flavobacteria (CF) community structure in the East China Sea (ECS) was investigated using a newly designed CF-specific 16S rRNA gene primer pair, revealing previously unknown high CF diversity in the ECS and a contrasting diversity pattern between the estuarine and open ocean regions. Phylogenetic analysis clustered 70 partial CF 16 rRNA gene sequences into 26 subgroups, including seven unique subgroups in the open ocean station, 17 unique subgroups in the estuarine station and two common subgroups. The CF species diversity was higher in the open ocean, whereas the CF subgroup diversity was higher in the estuarine region. At the species level, Flavobacteria and unclassified CF species were detected in both stations, whereas Sphingobacteria was only detected in the estuarine station. At the subgroup level, subgroups containing clones from various environments dominated both stations, whereas the soil, coast and freshwater subgroups occurred only in the estuarine station. This contrasting diversity pattern in the ECS can be attributed to the distinct difference in hydrological features between the estuarine and open ocean regions.