Assessing the potential for zinc limitation of marine primary production: proteomic characterization of the low zinc stress response in marine diatoms

Riss Kellogg, Ph.D, 2022
Mak Saito, Advisor

Marine diatoms are abundant photoautotrophic algae that contribute significantly to
photosynthetic carbon fixation and export throughout the oceans. Zinc is an important
micronutrient in algal metabolism, with scarce dissolved concentrations in the upper euphotic zone
reflecting high biological demand. In this thesis, I investigated the response of marine diatoms to
Zn scarcity to characterize metabolic mechanisms used to combat Zn stress. I began by assaying the
ability to metabolically substitute cobalt (Co) in place of Zn in four diatom species and found
that enhanced abilities to use Co are likely an adaptation to high surface dCo:dZn ratios in the
native environment. I next demonstrated that Zn/Co metabolic substitution in diatoms is not
universal using culture studies of Chaetoceros neogracile RS19, which has an absolute Zn
requirement. Using global proteomic analysis, I then identified and characterized diatom ZCRP-A and
ZCRP-B, a putative Zn-chaperone and membrane-tethered Zn acquisition protein, respectively, as two
proteins involved in the low-Zn response. I demonstrated that these proteins are widespread in
marine phytoplankton and can be deployed as protein biomarkers of Zn stress in the field. I
furthermore documented both the detection of ZCRPs in the Southern Ocean and the existence of Zn/Fe
co-limitation within the natural phytoplankton population in Terra Nova Bay, demonstrating that Zn
co-limitation can indeed occur in the field, even in high macronutrient waters. Lastly, I explored
the relative demand of Zn and cadmium (Cd) within the Southern Ocean community using stable ⁶⁷Zn
and ¹¹⁰Cd tracers, documenting a high demand for both metals during the austral 2017-2018 summer
season and investigating the cycling of these elements within this important region. Overall, this
dissertation provides new information regarding Zn acquisition and homeostasis mechanisms within
marine algae and demonstrates that Zn co-limitation in the field is not only possible, but detectable via protein biomarkers.