Presenter: Jesse McNichol (University of Southern California)

Description:
DNA-based methods have the potential to provide a holistic picture of marine ecosystems, but this requires sampling and analysis methods that quantify all community members. In this study, we report comprehensive measurements of microbial community composition using unfractionated (>0.2 µm) samples analyzed with universal, 3-domain PCR primers (515Y/926R) from the global sampling campaigns AMT, BioGEOTRACES, GO-SHIP, and POTATOE. Since our primers amplify both 16S and 18S sequences in a single PCR reaction, we were able to reconstruct both phytoplankton and heterotrophic community abundances in one internally-consistent assay. These data revealed large systematic changes in community composition across depth and primary productivity gradients. Most prokaryotic heterotrophs were ubiquitous at higher taxonomic levels (~ order) but biogeographic distributions of specific sequence types (ASVs) and ratios of higher-level groupings to one another differed significantly across the aforementioned gradients. These samples were sequenced at depths of at least hundreds of thousands of reads per sample; thus, we were able to quantify the abundance of rare but biogeochemically-important organisms, including diazotrophs, enabling comparisons with cell count estimates from nifH quantitative PCR data. Moving forward, we envision these datasets as a basis for investigating how biogeographic patterns change across space and time, how trait-based models such as DARWIN compare with real-world observations, and for discovering new biological interactions and associations of microbial taxa with geochemical covariates. Additionally, they can be used to inform trait-based models of marine prokaryotic heterotrophs and help investigators interpret 'omics data in a large-scale biogeochemical context. Finally, these datasets will be hosted on the Simons Collaborative Marine Atlas Project (CMAP), providing easy access to microbial abundance data and associated covariates.