Distribution of abundant prokaryotic organisms in the water column of the central Baltic Sea with an oxic-anoxic interface

Anoxic marine deeps are characterized by their chemically stratified water columns. This has implications for the vertical distribution of microbial assemblages, but knowledge of this distribution is still poor. To further evaluate these systems we investigated the Faro Deep (central Baltic Sea), which was anoxic in its bottom waters in August 2003. To resolve the vertical distribution of the dominating prokaryotic microorganisms along the physico-chemical gradients, we used 16S rRNA or 16S rRNA gene-based single strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE). Altogether, 43 microorganisms were differentiated by sequencing of gel bands; 55% of these belonged to Phylum Proteobacteria, 24% to Phylum Bacteroidetes, 7% to Class Actinobacteria, 5% to Phylum Cyanobacteria, 2% were distantly related to the genus Nitro-spina and 5% were identified as Phylum Crenarchaeota. Only 10% of the investigated assemblages were identified by both fingerprinting methods used. However, both methods revealed dominant 16S rRNA bands, the sequences of which were related to the following organisms: a phototrophic Synechococcus in the photic zone, an aerobic and heterotrophic Pseudoalteromonas in the oxic to suboxic zone, and an anaerobic and autotrophic nitrate-reducing Epsilonproteobacterium in the anoxic to sulphidic zone. The latter 2 bacterial taxa have also been reported from other anoxic basins and seem to be characteristic of marine pelagic redoxclines, indicating that these environments could harbor similar microbial communities.