Exploring Vitamin B1 Cycling and its Connections to the Microbial Community in the North Atlantic Ocean

Vitamin B₁ (thiamin) is an essential coenzyme for all cells, but the factors controlling the cycling of B₁, and its influence on plankton community structure and productivity are not understood. Recent metagenomic surveys have shown that many bacterioplankton are unable to synthesize B₁ completely, and require either the intact compound or a B₁ precursor molecule. To understand the environmental availability of B₁ and its influences on the microbial community, we developed a LCMS based method to quantify the dissolved concentrations of the most commonly required B₁ precursors that improves sensitivity and precision by roughly an order of magnitude from existing published methods. B₁ and all of its known precursors were detected in the northwestern Atlantic during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). Across all stations and depths dissolved concentrations ranged between 0.20-120 pM AmMP, 7.10-450 pM thiamin, 3.50-150pM cHET, 0.1-30pM HET, and 0.1-4.0 pM HMP. Substantial variability in concentrations was observed between stations, both in vertical distribution and overall concentration ranges. Additionally, the B₁ congener concentrations appear to be associated with different microbial community structures. B₁ concentrations in the two most southern stations were associated with the differential abundances of SAR11, Oceanospirillales, and Flavobacteria 16S amplicon sequence variants, which in turn can be related to the gene content and differential pathway gaps that are found across these broad bacterial groups. These associations suggest that B₁ mediated interactions between microbial taxa have substantial impacts on the overall structure of plankton communities.