Vertical Structure of Bacterial and Archaeal Communities within the Sediment of a Eutrophic Lake as Revealed by Culture-Independent Methods

The bacterial community composition and distribution of major bacterial phylogenetic groups, archaea, as well as the functional groups, from sediment of Lake Taihu were investigated by denaturing gradient gel electrophoresis of amplified 16S rDNA and fluorescence in situ hybridization. The microbial community changed with depth of sediments. Up to 30-50% of total DAPI (4', 6'-diamidino-2-phenylindole) cell counts were bacteria, while archaea reached as high as 5-10% of the total cell counts. beta-Proteobacteria was the most abundant group detected in upper sediment, accounting for up to 10-15% of total DAPI cell counts, and up to 11% of total DAPI cell counts belonged to gamma- Proteobacteria in lower sediment. Cyanobacteria accounted for up to 4-18% of total cell counts and were detected as deep as 45 cm in the sediment. For the nitrogen transformation functional groups, putative ammonia oxidation Archaea - Crenarchaeota counts increased with the depth, while the ammonia oxidation bacteria decreased with the depth, which indicated the nitrogen transformation ability in the sediments.