Exploring the potential for zinc toxicity in low manganese Southern Ocean phytoplankton

Marine diatoms have evolved complex traits and growth strategies to survive in the Southern Ocean where the bioactive trace metals iron (Fe) and manganese (Mn) are low in supply, yet metals such as zinc (Zn) can be in high concentrations. The same divalent metal transport system is thought to be used for Zn and Mn, which may result in excess Zn imported into cells and difficulty acclimating to low Mn concentrations. It is unclear whether Antarctic diatoms have adapted to this extreme chemical environment through the use of specialized transporters, efflux mechanisms, or Zn storage proteins compared to temperate phytoplankton counterparts. To address this, cultures are being grown in the lab with physiology (growth rates, cellular metal quotas) and transcriptomic experiments underway. Preliminary data suggests the temperate coccolithophore Geophyrocapsa huxleyi reaches Mn limitation under trace levels of Mn in seawater, while Southern Ocean diatoms have a reduced Mn requirement and can maintain higher growth levels relative to their maximum. Further, growth of the coccolithophore is suppressed under excess Zn levels, while Southern Ocean diatoms are unaffected. Transcriptomics will aid in identifying how these diatoms structure metabolic processes under Mn stress, which transporters are activated, and how excess Zn is managed in the Southern Ocean. Melting of sea ice and stratification with ocean warming is predicted to increase Fe supplies in the Southern Ocean, potentially expanding and exacerbating Mn stress. Such conditions may dictate species composition by favoring diatoms with evolved strategies for managing excess Zn and maximizing Mn specific uptake, while keeping high Mn-requiring phytoplankton such as coccolithophores out of the Antarctic zone. 

Presentation Preference: Poster

Primary Presenter: Natalie Cohen, University of Georgia (cohen@uga.edu)

Authors:

Nicholas Hawco, University of Hawaii  (hawco@hawaii.edu)

Lucy Quirk, University of Georgia  (lucye.quirk@gmail.com)

Tatiana Gamez, University of Hawaii  (gamez2@hawaii.edu)