ANT LIA: Collaborative Research: Mixotrophic Grazing as a Strategy to meet Nutritional Requirements in the Iron and Manganese Deficient Southern Ocean

Mixotrophic microorganisms that are capable of both photosynthetic and heterotrophic forms of metabolism are key contributors to primary productivity and organic carbon remineralization in the Southern Ocean. However, uncertainties in their grazing behavior and physiology prevent an accurate understanding of microbial food web dynamics and biogeochemical cycling in the Antarctic ecosystem. Polar mixotrophs have evolved to withstand extreme seasonality, including variable light, sea ice, temperature, and micronutrient concentrations. In particular, the Southern Ocean appears to be the only region of the world’s ocean where the bioessential trace metals iron (Fe) and manganese (Mn) are low enough to inhibit photosynthetic growth. The molecular physiology of mixotrophs experiencing Fe and Mn growth limitation has not yet been examined, and we lack an understanding of how seasonal changes in the availability of these micronutrients influence mixotrophic growth dynamics. We aim to examine whether grazing affords mixotrophs an ecological advantage in the Fe and Mn-deficient Southern Ocean, and to characterize the shifts in metabolic processes that occur during transitions in micronutrient conditions. Culture studies will directly measure growth responses, grazing behavior, and changes in elemental stoichiometry in response to Fe and Mn limitation. Transcriptomic analyses will reveal the metabolic underpinnings of trophic behavior and micronutrient stress responses, with implications for key biogeochemical processes such as carbon fixation, remineralization, and nutrient cycling.