Superoxide dismutase shapes manganese stoichiometry in Southern Ocean diatoms

Quantifying the elemental stoichiometry of marine phytoplankton biomass is crucial for projections of primary production. In many cases, the mechanistic underpinnings of biomass stoichiometry are unclear. We combined metaproteomics, Bayesian statistical modeling, and geochemical measurements to quantify the contribution of superoxide dismutases to metal stoichiometry in natural populations of Southern Ocean diatoms. Our analyses indicate that a substantial amount of manganese (Mn) in diatoms in an Antarctic polynya can be attributed to superoxide dismutases (∼0.7 micromoles of Mn:moles of carbon; ∼20% of the total cellular Mn quota). We then used proteomic profiles of polar diatom cultures to identify environmental controls on superoxide dismutases and found that Mn limitation induces the depletion of Mn superoxide dismutases and an accompanying increase in nickel superoxide dismutase. Overall, we combined metaproteomic approaches to quantify proteome composition and connected these measurements to metal-to-carbon ratios and their responses to metal availability. Our approach provides a mechanism for directly parameterizing ecosystem-scale models with molecular measurements.