Atlantic and Pacific Ocean bacterioplankton diversity

Large scale microbial biodiversity studies covering the major biogeographic provinces of the Atlantic and Pacific Oceans are still scarce but important to assess the global microbial oceanic biodiversity. To contribute to a more comprehensive picture, microbial diversity of three size fractions, >8 µm, 3-8µm and 0.2-3.0 µm, was investigated across latitudinal transects in the Atlantic (62°S-47°N) and Pacific (52°S-60°N) Ocean at five depths of the epipelagic and mesopelagic zone. A diverse set of biotic and abiotic variables was measured at each depth to assess correlations of microbial community variation with environmental properties. We chose the primer set 515F-Y/ 926R (V4-V5 region) for amplicon sequencing of the small rRNA subunit which covers long gene fragments, amplifies 18S rRNA genes and is less biased against abundant marine groups like SAR11 and Thaumarchaeota than commonly used 16S primers. To make a comparison between oceans possible, sequences were analyzed based on exact Amplicon Sequence Variants (ASVs) that differ from each other at specific bases, in contrast to OTUs which are clusters of similar sequences and not comparable between data sets. To verify library preparation and sequencing runs, artificial mock communities for 16S and 18S fragments were sequenced together with ocean samples and matched with their true composition. Data of the Atlantic Ocean samples showed that bacterial diversity was highest in mid–latitudinal regions and at temperatures of 15°C-20°C and significant correlations with some of the other abiotic and biotic variables were found. First insights provide evidence for rather similar general patterns in the Pacific Ocean but with some distinct differences on a microdiversity level.