B-Vitamin Competition: Intracellular and Dissolved B-Vitamins Provide Insight into Marine Microbial Community Dynamics

The availability of B-vitamins has the ability to directly affect the dynamics of the marine microbial community. Here we show, for the first time, the connection between dissolved and intracellular B-vitamins in a marine environmental community. Two incubation experiments were conducted at a long-term study site (SPOT) in the San Pedro Basin off the coast of Los Angeles, CA. Experiments were conducted in oligotrophic, preupwelling conditions. Due to the 2015 El Niño event, the seasonal upwelling at SPOT did not occur, creating unusually nutrient depleted conditions. Vitamins B₁, B₇, and B₁₂ were added in addition to macronutrients at concentrations similar to typical SPOT upwelling conditions. Intracellular and dissolved B-vitamin analyses were conducted to determine shifts in cellular B-vitamin requirements as a function of growth rate. We observed a significant bacterioplankton and phytoplankton growth responses with the addition of B-vitamins in a manner that appears to match the enzymatic requirements for these compounds (e.g. B₁>B₇>B₁₂). Intracellular B-vitamin analysis of T₀ samples support this observation, as all four forms of B₁₂ were not detectable within cells, yet multiple forms of B₁ and B₇ were detected at or near levels previously reported. Treatments with B₁₂ and macronutrients were observed to have the greatest growth rates. This finding, in addition to the apparent lack of intracellular B₁₂ in the initial community, appears to indicate that the initial microbial community was limited by B₁₂. The addition of each vitamin caused a distinct shift in the blooming microbial community. Our results demonstrate that B-vitamins strongly influence not only the growth rate, but also the species composition and species succession of the microbial community as a whole. Large-scale changes to upwelling regimes are predicted in the future ocean; our results indicate that B-vitamins will have a substantial role in controlling microbial community dynamics under these future conditions.