B vitamins are some of the most commonly required biochemical cofactors in living systems. Therefore, cellular metabolism of marine vitamin-requiring (auxotrophic) phytoplankton and bacteria would likely be significantly compromised if B vitamins (thiamin B 1 , riboflavin B 2 , pyridoxine B 6 , biotin B 7 , and cobalamin B 12 ) were unavailable. However, the factors controlling the synthesis, ambient concentrations, and uptake of these key organic compounds in the marine environment are still not well understood. Here, we report vertical distributions of five B vitamins (and the amino acid methionine) measured simultaneously along a latitudinal gradient through the contrasting oceanographic regimes of the southern California-Baja California coast in the Northeast Pacific margin. Although vitamin concentrations ranged from below the detection limits of our technique to 30 pM for B 2 and B 12 and to ∼500 pM for B 1 , B 6 , and B 7 , each vitamin showed a different geographical and depth distribution. Vitamin concentrations were independent of each other and of inorganic nutrient levels, enriched primarily in the upper mesopelagic zone (depth of 100-300 m), and associated with water mass origin. Moreover, vitamin levels were below our detection limits (ranging from ≤0.18 pM for B 12 to ≤0.81 pM for B 1 ) in extensive areas (100s of kilometers) of the coastal ocean, and thus may exert important constraints on the taxonomic composition of phytoplankton communities, and potentially also on rates of primary production and carbon sequestration.T he evolution of organic catalysts (enzymes and coenzymes) that accelerated biochemical reactions by orders of magnitude compared with inorganic catalysis alone was a critical step for the emergence of major cellular processes (1). Well-known coenzyme molecules include the B vitamins, which catalyze many important biochemical reactions in central metabolism (2). Those reactions include rearrangement-reduction of C-C bonds and methyl transfer reactions, synthesis of deoxyribose/fatty acids/ carbohydrates/branched-chain amino acids, electron transfer in oxidation-reduction reactions, and CO 2 fixation (2). This means that without an exogenous source of B vitamins, central metabolism in vitamin-requiring (auxotrophic) organisms would be compromised and the cells would not be able to grow, a situation that could have great bearing on many biological processes in the ocean, including the biological carbon pump.In the marine environment, vitamins have been implicated as important factors regulating the growth and succession of phytoplankton species (3). This inference was based on the fact that many species of eukaryotic phytoplankton require vitamins when they are cultured in the laboratory (3-7). Although it was thought that marine prokaryotes were the major producers of vitamins in the sea (4), genomic data indicate that it is common for both eukaryotic phytoplankton and bacterioplankton to be auxotrophic for at least one B vitamin, mainly because they lack the complete biosynthetic...

All known phototrophic metabolisms on Earth rely on one of three categories of energy-converting pigments: chlorophyll-a (rarely -d), bacteriochlorophyll-a (rarely -b), and retinal, which is the chromophore in rhodopsins. While the significance of chlorophylls in solar energy capture has been studied for decades, the contribution of retinal-based phototrophy to this process remains largely unexplored. We report the first vertical distributions of the three energy-converting pigments measured along a contrasting nutrient gradient through the Mediterranean Sea and the Atlantic Ocean. The highest rhodopsin concentrations were observed above the deep chlorophyll-a maxima, and their geographical distribution tended to be inversely related to that of chlorophyll-a. We further show that proton-pumping proteorhodopsins potentially absorb as much light energy as chlorophyll-a–based phototrophy and that this energy is sufficient to sustain bacterial basal metabolism. This suggests that proteorhodopsins are a major energy-transducing mechanism to harvest solar energy in the surface ocean.

We have developed a new method to directly measure the concentration of the particulate and dissolved pools of B-vitamins in seawater. B-vitamins are coenzymes required for life, yet many organisms cannot synthesize these compounds de novo and must scavenge them from the environment. It has been shown that B-vitamins can control the marine microbial community's structure and activity; however, the actual B-vitamin requirements/quotas for marine microbes are not well studied due to the lack of analytical protocols. This method will enable the study of B-vitamin cellular quotas as well as their environmental cycling. With this method, we can also simultaneously determine the biochemical congeners of vitamins B 1 and B 12 , as well as vitamins B 2 , B 6 , B 7 , and the amino acid methionine in both the particulate and dissolved pool, using liquid chromatography-mass spectrometry after a chemical extraction (particulate) or resin preconcentration (dissolved). Particulate and dissolved B-vitamin concentrations were simultaneously determined from a microbial community in the Atlantic Ocean. Particulate B-vitamin concentrations in the Atlantic ranged from 0.01 pM (cyano-B 12 ) to 46.4 pM (thiamin monophosphate, a B 1 congener) while dissolved B-vitamin concentrations ranged from 0.07 pM (adenosyl-B 12 ) to 679.4 pM (B 7 ). The application of this technique in different marine systems has the potential to shed new light on previously unknown biochemical processes occurring within the oceanic microbial community, and the resulting roles B-vitamins play in regulating global biogeochemical cycles.

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