Analyzing biogeographical patterns of microbial communities from the Atlantic Ocean and the characterization of the microbial community and toxicity from the dinoflagellate Prorocentrum cordatum ; Analyse biogeografischer Muster mikrobieller Gemeinschaften aus dem Atlantischen Ozean und Charakterisierung der mikrobiellen Gemeinschaft und Toxizität des Dinoflagellaten Prorocentrum cordatum

Marine microorganisms fuel marine life and directly influence biochemical cycles on a planetary scale. Their study, as independent individuals, and the microbial communities they belong to, is crucial for understanding the marine ecosystem. Therefore, the work presented here is divided into two parts. In the first part, via taxonomic diversity and co-occurrence analysis, we compared and explored the biogeography of microbial communities at a basin scale, specifically from the Atlantic Ocean. Second, we focus on studying the cosmopolitan, bloom-forming dinoflagellate Prorocentrum cordatum by characterizing its microbiome, growth patterns, and toxic activity when grown at three different temperatures. 1. High-throughput sequencing of rRNA genes provides community composition at high resolution, yet it is unclear how the choice of primers affects biogeographic patterns. We re-amplified 16S rRNA genes from DNA sampled during R/V Polarstern Cruise ANT28-5 over a latitudinal transect across the Atlantic Ocean from 52°S to 47°N using universal primers covering the V4-V5 regions of the 16S rRNA gene and compared the results with those obtained previously with V5-V6 bacteria-specific primers. A U-shaped distance-decay relationship and a decrease in bacterioplankton diversity in equatorial latitudes compared to mid-latitudes were maintained on the new dataset. However, a change in methodology generated differences in patterns based on community richness and in community composition, such as differences in the relative abundance of SAR11 clades. The V4-V5 provided archaea and 18S communities not analyzed previously with the V5-V6 primer set. A bimodal latitudinal diversity gradient was also observed for archaea and micro-eukaryotes. However, only archaea richness peaked at 15–20°C, and the U-shaped distance-decay relationship was present only for the particle-associated archaea community. We complemented the biogeographical patterns with co-occurrence network analysis, providing evidence of geographical co-occurrence ...