Biogeochemical Insights into B-Vitamins in the Coastal Marine Sediments of San Pedro Basin, CA

Abstract:

 Coastal marine sediments support a high abundance of mircoorganisms which play key roles in the cycling of nutrients, trace metals, and carbon, yet little is known about many of the cofactors essential for their growth, such as the B-vitamins. The suite of B-vitamins (B₁, B₂, B₆, B₇, B₁₂) are essential across all domains of life for both primary and secondary metabolism. Therefore, studying sediment concentrations of B-vitamins can provide a biochemical link between microbial processes and sediment geochemistry. Here we present B-vitamin pore water concentrations from suboxic sediment cores collected in September 2014 from San Pedro Basin, a silled, low oxygen, ~900 m deep coastal basin in the California Borderlands. We compare the B-vitamin concentrations (measured via LCMS) to a set of geochemical profiles including dissolved Fe (65-160 µM), dissolved Mn (30-300 nM), TCO₂, solid phase organic carbon, and δ¹³C. Our results show high concentrations (0.8-3nM) of biotin (B₇), commonly used for CO₂ fixation as a cofactor in carboxylase enzymes. Thiamin (B₁) concentrations were elevated (20-700nM), consistent with previous pore water measurements showing sediments could be a source of B₁ to the ocean. Cobalamin (B₁₂), a cofactor required for methyl transfers in methanogens, was also detected in pore waters (~4-40pM). The flavins (riboflavin [B₂] and flavin mononucleotide[FMN]), molecules utilized in external electron transfer, showed a distinct increase with depth (10-90nM). Interestingly, the flavin profiles showed an inverse trend to dissolved Fe (Fe decreases with depth) providing a potential link to culture experiments which have shown extracellular flavin release to be a common trait in some metal reducers. As some of the first B-vitamin measurements made in marine sediments, these results illustrate the complex interaction between the microbial community and surrounding geochemical environment and provide exciting avenues for future research.