Marine microbial communities produce and cycle organic matter in the ocean. Some of this organic matter is in the form of metabolites, small, organic biomolecules that are present both inside of microbial cells and dissolved in seawater. Studying metabolite dynamics provides insights into the fate of a significant portion of marine primary production as well as microbial community interactions that influence short and long term carbon storage in the ocean. Here I analyzed both dissolved (extracellular) and particulate (intracellular) metabolites from the 2019 Gradients 3 (G3) research cruise that were collected along a latitudinal transect. Sampling stations spanned the North Pacific Subtropical Gyre, an area with low nutrients and primary productivity, to the North Pacific Subpolar Gyre, an area with higher nutrients and primary productivity. I extracted particulate metabolites using a modified Bligh and Dyer extraction and dissolved metabolites using cation-exchange solid phase extraction. I acquired metabolite data using liquid chromatography mass spectrometry and processed the data using Skyline software. In both dissolved and particulate samples, metabolite pools were dominated by compatible solutes, compounds organisms use for handling osmotic stress, as well as amino acids. Metabolite abundances in both phases largely increased traveling northwards along the transect, reflecting increases in productivity, microbial biomass, and nutrients. However, certain metabolite concentrations did not follow this trend, suggesting that differences in microbial community composition or physiology may play an important role in regulating the synthesis of these compounds. These results show how varying environmental conditions affect the composition of organic matter produced by marine microbial communities. This information can be used in to predict how marine primary producers will store and use carbon in a future changed ocean.

Phytoplankton play a pivotal role in marine ecosystems by providing essential nutrients and energy to heterotrophic microorganisms through the release of low molecular weight (LMW) metabolites into the dissolved organic matter (DOM) pool. Ectoine, a compatible solute primarily sourced from bacteria, acts as a safeguard against osmotic stress. In this study, we investigate the intricate interaction between phytoplankton and bacteria consumers by comparing the growth dynamics of two diatom species, Thalassiosira pseudonana and Thalassiosira oceanica, in the presence of ectoine. Cultures of T. pseudonana and T. oceanica were cultivated under axenic, controlled conditions, and their growth was monitored using measurements of relative fluorescence units, cell enumeration techniques, and metabolomics analysis. Our hypothesis suggests that samples with ectoine will exhibit higher metabolite abundance and growth rates compared to those without. Through a comparative analysis between cultures supplemented with ectoine and those without, this research endeavors to shed light on producer-consumer interactions within controlled laboratory settings, offering valuable insights in the complex microbial dynamics prevalent in oceanic environments.