Characterization of the bacterial community composition in a hypoxic zone induced by Microcystis blooms in Lake Taihu, China

Cyanobacterial blooms have become more frequent as a result of eutrophication in lakes. The accumulation and breakdown of huge cyanobacterial biomasses often cause hypoxia in lakes. However, little is known about microbial diversity in these areas. In this study, we characterized the bacterial community composition of a Microcystis-bloom-induced hypoxic area in Lake Taihu, which is a large, shallow lake, by analysing terminal restriction fragment length polymorphisms of 16S ribosomal RNA genes and clone libraries generated from selected samples. Bacterial samples were collected at different sites within the hypoxic zone at different times during the development of hypoxia. The results showed that the composition of both free-living and particle-attached bacterial communities in the water column varied spatially and temporally and that these variations were largely related to changes in the concentrations of dissolved oxygen and ions in the water column. Sequences affiliated with Clostridium were predominantly found at the onset of hypoxia, whereas members of the LD12 cluster were detected at the posthypoxia stage; Desulfovibrio and Comamonadaceae dominated throughout the hypoxic event. We speculate that these organisms may be associated with the decomposition of Microcystis biomass and the production of volatile organic compounds; however, their specific function in Microcystis-bloom-induced hypoxia warrants further study.