Distribution of major bacterioplankton groups in the Atlantic Ocean

The focus of this PhD thesis was to explore in unprecedented resolution the distribution of individual microbial groups in the upper 500 m of different ecological provinces by CARD-FISH with rRNA-targeted oligonucleotide probes targeting major bacterial and archaeal clades. Automated microscopic analysis of samples showed specific distribution patterns for the individual microbial groups. A similar prokaryotic community composition could be found in the photic zone of the entire Atlantic Ocean, but it was largely different from the community in the aphotic zone.A second project focused on the characterization of the flow cytometrically defined high nucleic acid (HNA) and low nucleic acid (LNA) fraction of bacterioplankton. HNA samples from the productive province were dominated by Bacteroidetes while Prochlorococcus dominated the oligotrophic province. Other groups present in the diverse HNA fraction were Alpha- and Gammaproteobacteria including their respective subgroups Roseobacter and SAR86. In contrast, about two-thirds of the LNA fraction was comprised of the single clade SAR11 and only small proportions of Beta- and Gammaproteobacteria.