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Polar Phytoplankton Need Zinc to Cope with the Cold

Antarctic algae need their vitamins; zinc fuels some of their most important functions.

Photograph of a stream of diatoms beneath Arctic sea ice.

A view beneath Arctic sea ice, of the diatoms Melosira arctica (Lianna Nixon, taken using a ROV)

Even in the chilly waters of Antarctica, tiny ocean-dwellers called phytoplankton play an outsize role in cycling carbon and nutrients. These microscopic algae have managed to adapt to a unique set of conditions in polar waters, including vast shifts in sunlight and frigid temperatures. These waters also contain higher concentrations of the essential trace metal zinc, compared to other oceans. That zinc turns out to be extremely important for polar phytoplankton. 

After peering into the function and activity of phytoplankton genes and looking at how communities of these microalgae interact, researchers have found that polar algae rely on dissolved zinc to photosynthesize.

Thomas Mock, a marine microbiologist at the University of East Anglia, leads this effort to understand what makes polar photosynthesizers tick. He’s working with researchers at the U.S. Department of Energy (DOE) Joint Genome Institute (JGI), a DOE Office of Science User Facility located at Lawrence Berkeley National Laboratory (Berkeley Lab) through the JGI Community Science Program (CSP).  Through this collaboration, in 2017, they published the first genome sequence of a cold-adapted microalga: the diatom Fragilariopsis cylindrus. At that time, they noted that the F. cylindrus genome encoded more proteins requiring zinc than non-polar algae. They hypothesized that perhaps elevated zinc in polar waters let phytoplankton evolve to colder temperatures characteristic for polar oceans.

Microscope images of the antarctic green alga Microglena sp. YARC.

The Antarctic green alga Microglena sp. YARC under an optical microscope (Left) and a transmission electron microscope (Right) (Xiaowen Zhang)

In this study, they’ve cracked open the genome of another polar species, the green alga Microglena sp. YARC, which also contains expanded genes for proteins requiring zinc. Co-expression analysis as well as laboratory culture experiments showed that those zinc-binding proteins are important for primary metabolism such as photosynthesis and gene regulation. 

Mock and his team then linked those species-level observations with data on microalgal communities across different ocean latitudes from pole to pole, using metatranscriptome and metagenome data from the JGI.

With multiple threads of evidence showing that zinc has allowed polar algae to inhabit their frigid environment, Mock pointed out that as climate change warms polar waters, changes in trace metal concentrations will also affect photosynthesizers – algae need their essential nutrients, too. 

This work is part of a long-term collaboration with the JGI Algal Program, which explores genomics of algal diversity and biology to support basic science as well as bioenergy and biomanufacturing. The JGI Algal Program makes genomes and multi-omics data from JGI CSP projects publicly available at the PhycoCosm portal.

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Byline: Menaka Wilhelm