COBALAMIN AND OTHER B-VITAMINS IN THE NORTHWEST ATLANTIC OCEAN

Abstract

B-vitamins, like cobalamin (B12), are essential micronutrients that impact marine microbial community composition and activity in various parts of the ocean. Although their influence on marine microorganisms has been known for decades, obtaining reliable quantitative measurements of these metabolites remains challenging and impedes our understanding of their dynamics in situ. In this thesis, I measure b-vitamins in cultures and environmental communities filling in critical knowledge gaps about their concentrations, distributions, and their underlying dynamics in the Northwest Atlantic Ocean. In Chapter 1, I explore the history and importance of studying cobalamin in the ocean. In Chapter 2, I confront the puzzling measurements of photolabile cobalamin forms in the sunlit ocean. I provide cobalamin form-specific photodegradation rates and quantitative evidence that OH-B12 should be the dominant cobalamin form in the sunlit ocean. Additionally, I identify novel photodegradation products through high resolution mass spectrometry that may be important metabolites to microbial communities. I leverage this knowledge in Chapter 3, where I quantify b-vitamins and related compounds in both particulate (intracellular) and dissolved (extracellular) samples from the Halifax Line in the Northwest Atlantic Ocean over 5 years at different stations, depths, and seasons. From this, I identify unique spatiotemporal patterns in their distribution and stoichiometry, a fundamental step for future studies of b-vitamins in the ocean. I also identify seasonally distinct cobalamin dynamics in the Northwest Atlantic Ocean, from cobalamin co-limitation after the spring diatom bloom to a community that remodels cyanobacterially produced, pseudo-cobalamin, to cobalamin in the fall. The importance of cobalamin remodeling inspired the work performed in Chapter 4, where we interrogated factors that influence pseudocobalamin production, use, and quota in Synechococcus sp. WH8102. We show that the pseudocobalamin quota is variable in cultures, depending on growth phase, condition, and cultivation methods, but surprisingly consistent in natural Synechococcus communities. This dissertation offers insight into the b-vitamins, particularly the complex dynamics they underpin and embody through their variability, distribution, and influence in marine microbial communities. It also raises further questions about this charismatic group of metabolites and provides an analytical foundation for future work which looks to answer them.