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Organic carbon in seawater plays a significant role in the global carbon cycle. The concentration and composition of dissolved organic carbon reflect the activity of the biological community and chemical reactions that occur in seawater. From 2016 to 2019, we repeatedly sampled the oligotrophic northwest Sargasso Sea in the vicinity of the Bermuda Atlantic Time‐series Study site (BATS) to quantitatively follow known compounds within the pool of dissolved organic matter in the upper 1000 m of the water column. Most metabolites showed surface enrichment, and 83% of the metabolites had significantly lower concentrations with increasing depth. Dissolved metabolite concentrations most notably revealed temporal variability. Fourteen metabolites displayed seasonality that was repeated in each of the 4 yr sampled. Concentrations of vitamins, including pantothenic acid (vitamin B5) and riboflavin (vitamin B2), increased annually during winter periods when mixed layer depths were deepest. During diel sampling, light‐sensitive riboflavin decreased significantly during daylight hours. The temporal variability in metabolites at BATS was less than the spatial variability in metabolites from a previous sample set collected over a broad latitudinal range in the western Atlantic Ocean. The metabolites examined in this study are all components of central carbon metabolism. By examining these metabolites at finer resolution and in a time‐series, we begin to provide insights into the chemical compounds that may be exchanged by microorganisms in marine systems, data which are fundamental to understanding the chemical response of marine systems to future changes in climate.

Metabolites, or the small organic molecules that are synthesized by cells during metabolism, comprise a complex and dynamic pool of carbon in the ocean. They are an essential currency in interactions at the population and community levels of biological organization. Characterizing metabolite distributions inside microbial cells and dissolved in seawater is essential to understanding the controls on their production and fate, as well as their roles in shaping marine microbial food webs. Here, we apply a targeted metabolomics method to quantify particulate and dissolved distributions of a suite of biologically relevant metabolites including vitamins, amino acids, nucleic acids, osmolytes, and intermediates in biosynthetic pathways along a latitudinal transect in the western Atlantic Ocean. We find that, in the upper 200 m of the water column, most particulate or intracellular metabolites positively covary with the most abundant microbial taxa. In contrast, dissolved metabolites exhibited greater variability with differences in distribution between ocean regions. Although fewer particulate metabolites were detected below 200 m, the particulate metabolites identified in the deep ocean may be linked to adaptive physiological strategies of deep‐sea microbes. Based on the identified metabolite distributions, we propose relationships between certain metabolites and microbial populations, and find that dissolved metabolite distributions are not directly related to their particulate abundances.

Marine sinking particles transport carbon from the surface and bury it in deep‐sea sediments, where it can be sequestered on geologic time scales. The combination of the surface ocean food web that produces these particles and the particle‐associated microbial community that degrades them creates a complex set of variables that control organic matter cycling. We use targeted metabolomics to characterize a suite of small biomolecules, or metabolites, in sinking particles and compare their metabolite composition to that of the suspended particles in the euphotic zone from which they are likely derived. These samples were collected in the South Atlantic subtropical gyre, as well as in the equatorial Atlantic region and the Amazon River plume. The composition of targeted metabolites in the sinking particles was relatively similar throughout the transect, despite the distinct oceanic regions in which they were generated. Metabolites possibly derived from the degradation of nucleic acids and lipids, such as xanthine and glycine betaine, were an increased mole fraction of the targeted metabolites in the sinking particles relative to surface suspended particles, while algal‐derived metabolites like the osmolyte dimethylsulfoniopropionate were a smaller fraction of the observed metabolites on the sinking particles. These compositional changes are shaped both by the removal of metabolites associated with detritus delivered from the surface ocean and by production of metabolites by the sinking particle‐associated microbial communities. Furthermore, they provide a basis for examining the types and quantities of metabolites that may be delivered to the deep sea by sinking particles.

Microbes, the foundation of the marine foodweb, do not function in isolation, but rather rely on molecular level interactions among species to thrive. Although certain types of interactions between autotrophic and heterotrophic microorganisms have been well documented, the role of specific organic molecules in regulating inter-species relationships and supporting growth are only beginning to be understood. Here, we examine one such interaction by characterizing the metabolic response of a heterotrophic marine bacterium, Ruegeria pomeroyiDSS-3, to growth on dimethylsulfoniopropionate (DMSP), an abundant organosulfur metabolite produced by phytoplankton. When cultivated on DMSP, R. pomeroyisynthesized a quorum-sensing molecule, N-(3-oxotetradecanoyl)-l-homoserine lactone, at significantly higher levels than during growth on propionate. Concomitant with the production of a quorum-sensing molecule, we observed differential production of intra- and extracellular metabolites including glutamine, vitamin B2and biosynthetic intermediates of cyclic amino acids. Our metabolomics data indicate that R. pomeroyichanges regulation of its biochemical pathways in a manner that is adaptive for a cooperative lifestyle in the presence of DMSP, in anticipation of phytoplankton-derived nutrients and higher microbial density. This behavior is likely to occur on sinking marine particles, indicating that this response may impact the fate of organic matter.

Microbes, the foundation of the marine foodweb, do not function in isolation, but rather rely on molecular level interactions among species to thrive. Although certain types of interactions between autotrophic and heterotrophic microorganisms have been well documented, the role of specific organic molecules in regulating inter-species relationships and supporting growth are only beginning to be understood. Here, we examine one such interaction by characterizing the metabolic response of a heterotrophic marine bacterium, Ruegeria pomeroyi DSS-3, to growth on dimethylsulfoniopropionate (DMSP), an abundant organosulfur metabolite produced by phytoplankton. When cultivated on DMSP, R. pomeroyi synthesized a quorum-sensing molecule, N-(3-oxotetradecanoyl)-l-homoserine lactone, at significantly higher levels than during growth on propionate. Concomitant with the production of a quorum-sensing molecule, we observed differential production of intra- and extracellular metabolites including glutamine, vitamin B2and biosynthetic intermediates of cyclic amino acids. Our metabolomics data indicate that R. pomeroyi changes regulation of its biochemical pathways in a manner that is adaptive for a cooperative lifestyle in the presence of DMSP, in anticipation of phytoplankton-derived nutrients and higher microbial density. This behavior is likely to occur on sinking marine particles, indicating that this response may impact the fate of organic matter.

Calmodulin is an essential regulator of intracellular processes in response to extracellular stimuli mediated by a rise in Ca2+ion concentration. To profile protein-protein interactions of calmodulin in human brain, we probed a high content human protein array with fluorophore-labeled calmodulin in the presence of Ca2+. This protein array contains 37,200 redundant proteins, incorporating over 10,000 unique human neural proteins from a human brain cDNA library. We designed a screen to find high affinity (KD≤ 1 µm) binding partners of calmodulin and identified 76 human proteins from all intracellular compartments of which 72 are novel. We measured the binding kinetics of 74 targets with calmodulin using a high throughput surface plasmon resonance assay. Most of the novel calmodulin-target complexes identified have low dissociation rates (koff≤ 10−3s−1) and high affinity (KD≤ 1 µm), consistent with the design of the screen. Many of the identified proteins are known to assemble in neural tissue, forming assemblies such as the spectrin scaffold and the postsynaptic density. We developed a microarray of the identified target proteins with which we can characterize the biochemistry of calmodulin for all targets in parallel. Four novel targets were verified in neural cells by co-immunoprecipitation, and four were selected for exploration of the calmodulin-binding regions. Using synthetic peptides and isothermal titration calorimetry, calmodulin binding motifs were identified in the potassium voltage-gated channel Kv6.1 (residues 474–493), calmodulin kinase-like vesicle-associated protein (residues 302–316), EF-hand domain family member A2 (residues 202–216), and phosphatidylinositol-4-phosphate 5-kinase, type I, γ (residues 400–415).