Spatiotemporal dynamics of bacterial community composition in large shallow eutrophic Lake Taihu: High overlap between free-living and particle-attached assemblages

In eutrophic lakes, heterotrophic bacteria are closely associated with algal detritus and play a crucial role in nutrient cycling. However, the seasonal and spatial dynamics of free-living (FL) and particle-attached (PA) bacteria and the environmental factors shaping this relationship remain poorly understood. To address this issue, we explored the spatiotemporal patterns of bacterial community composition (BCC) in Lake Taihu, China, using terminal restriction fragment length polymorphism (T-RFLP) and 454-tag pyrosequencing of 16S rRNA gene. We generated a total of 218,027 high quality non-cyanobacterial sequence reads that resulted in 4940 OTUs (97% cutoff), with Actinobacteria, beta- and alpha-proteobacteria being the predominant taxa. Although PA communities contained significantly higher alpha-diversity than FL ones, we found that 59% of OTUs, that accounted for 96% of the total reads, were shared by both communities. The high degree of overlap between FL and PA communities indicates a high rate of dispersal potential, highlighting an underestimated connectivity and potentially similar ecological role for these two components. Distinct seasonal trends were recorded in both FL and PA communities, while spatial differences in BCC were small. In addition, both FL and PA bacterial communities exhibited similar patterns and synchrony, correlated to water temperature, nitrate and total suspended solids (TSS). Accordingly, the effects of eutrophication and hydrodynamics on the phylogenetic overlap and diversity between FL and PA communities were discussed.