In the present work sediments of the backbarrier tidal flat of the island of Spiekeroog were investigated by molecular techniques down to a depth of 5.5 meters. The microbial communities of the bacteria, archaea and eukarya were analyzed using domain-specific PCRprimers. The obtained amplicons were separated by DGGE and sequenced afterwards. The sequences gave an extensive insight into the composition of microbial communities within the sediment columns of different sites of the tidal flat. It was shown, that the sediment surfaces were dominated by Proteobacteria, whereas in deeper and older layers Chloroflexi were detected primarily. Thus a shift was observed from the dominating bacteria to organisms that up to now have mainly been found within deep subsurface or deep biosphere habitats. Methanogenic archaea were found within the whole sediment column, while members of the Methanosarcina were detectable in all layers indicating a coexistence with sulfate-reducing bacteria. This has been confirmed by the methane profile as methane was also detected in all layers. Sequences of eukarya were also found over the complete length of the investigated cores. Unexpectedly, a new cluster within the Euryarchaeota (TF1-cluster) was discovered during this analysis from a depth of 160 cm downwards, although eukarya-specific PCRprimers have been used.
The sediment cores which were recovered at different seasons were examined additionally to the sequence analysis by real-time PCR. Bacterial and archaeal cell numbers were calculated by quantifying their 16S rRNA-genes. The sulfate-reducing and methanogenic prokaryotes were quantified by means of key-enzymes for sulfate reduction (dissimilatory sulfite reductase; dsr) and methanogenesis (methyl coenzyme M reductase; mcr), respectively. Increasing cell numbers of bacteria and archaea, and also elevated copy numbers of dsr and mcr genes were detected at the sulfate-methane transition zones, where an anaerobe oxidation of methane (AOM) might take place. During sequencing of the corresponding DGGE-bands, the organisms postulated for AOM (ANME) were not detected. Nevertheless, the occurance of this process within the sulfate-methane transition zones can be concluded from the increased numbers of cells and gene copies. |