Research

B. Engelen, H. Sass, B. Köpke, R. Wilms

Microbial diversity and activities within the subsurface of tidal flat sediments

Tidal flats are young and dynamic ecosystems showing intense microbial activities along the depth profile of the sediment column. To analyse microbial communities within the sediment subsurface, we have used a combination of geochemical, microbiological and molecular biological techniques. This polyphasic approach was applied to sediment cores taken at different sampling sites from the sediment surface down to a depth of 5.5 m. The molecular biological investigation by DGGE revealed that different compartments of the sediments were characterized by specific microbial communities. The upper layers were dominated by various Proteobacteria. Below this zone, a dramatical shift to the Chloroflexus group, a typical deep subsurface phylum, was observed. A slightly different shift was also detected by the cultivation approach. In total, 112 pure cultures were isolated and grouped into 53 different operational taxonomical units. In deeper sediment layers almost exclusively endospore-forming bacteria were detected. To link the information of who is there with geochemical profiles, the abundance of sulfate reducers and methanogens was determined by quantitative PCR. Additionally, exoenzyme activities and sulfate reduction rates were measured.