New species of marine plankton discovered, an overlooked source of
nutrients in the oceans

Date:
February 11, 2022
Source:
University of Hawaii at Manoa
Summary:
A team of researchers has discovered two new and unusual species of
diatoms in the waters off Hawai'i. The organisms were also found
to fix nitrogen, a critical process that supports productivity in
the nutrient- poor open ocean they inhabit.



FULL STORY ==========================================================================
A team of University of Hawai'i at Manoa researchers in the Department of Oceanography's Center for Microbial Oceanography -- Research and Education
(C- MORE), along with collaborators at the University of California
Santa Cruz, and the California State University San Marcos, have just
published a paper in Nature Communicationsannouncing the discovery of
two new and unusual species of diatoms in the waters off Hawai'i. The
organisms were also found to fix nitrogen, a critical process that
supports productivity in the nutrient-poor open ocean they inhabit.


========================================================================== Diatoms, with their intricately patterned cell walls made of
glassy silica, are some of the most well-known and charismatic
phytoplankton. They fare best in nutrient-rich conditions. In the
nutrient-poor open ocean waters around Hawai'i, diatoms struggle
to acquire enough nitrogen to grow. To solve this problem, some
diatoms have established symbiotic relationships with nitrogen-
fixing cyanobacteria. These special endosymbiotic cyanobacteria can
take dissolved nitrogen gas -- which is plentiful in seawater but
not accessible to the diatoms -- and convert it into ammonia, a form
of nitrogen that the diatoms can easily use, but which is otherwise
exceedingly sparse in the open ocean. By harboring the cyanobacteria
inside their glass houses, diatoms have their own personal nitrogen
generators. They become a self-fertilizing system.

"Oceanographers have known about these diatom-cyanobacteria symbioses
in waters around Hawai'i for many years," said Christopher Schvarcz,
C-MORE researcher and the lead author on the study, "but the species we discovered are something quite different." The better known examples
of these types of symbioses are very easy to spot under the microscope,
because the diatom hosts are large "centric" cells with radial symmetry,
and the cyanobacterial endosymbionts living inside them form chains of
cells that emit a bright yellow-orange fluorescent glow when illuminated
with blue light.

The new diatom species isolated by Schvarcz are smaller and belong to a different lineage with an elongated, or "pennate" shape with bilateral symmetry. Their symbionts are also smaller, unicellular, and do not glow
under fluorescent light because they do not contain chlorophyll, making
them nearly invisible inside the diatom. This likely explains why they
had gone undetected for so long. Schvarcz discovered the new species by
adding samples of seawater to nitrogen-poor growth medium in the lab,
then carefully examining the cultures under a microscope over a period
of weeks and months to see what sorts of phytoplankton would grow.

"The results were a surprise," said Grieg Steward, a UHM professor who
worked with Schvarcz on the project. "The new diatoms are related to
species found in freshwater. We had no idea we would find their cousins thriving far out in the open sea. Chris's work is an important reminder
of how much one can still learn with a little patience and careful observation!" Another surprise came when the team measured the daily
patterns of nitrogen fixation of the cultures. Species that had been
studied previously tend to concentrate their nitrogen fixation activity
either during the day or at night, but not both.

"With these new species, we found an unusual hybrid pattern," said Sam
Wilson, a researcher in CMORE who led the effort to measure the nitrogen fixation rates of the cultures using custom-built equipment. "These cells
fix nitrogen starting in darkness around midnight and continue all the
way through the morning, afternoon, and into the early evening. Then they
take a six-hour break around sunset. We don't know why they do this yet,
but finding this odd pattern is exciting, because it means we are about to learn something new about an old process." The discovery and cultivation
of these species opens many exciting avenues of further research.

"Now that we know these species exist, we can study their ecology and
begin to understand their importance to the ocean's nitrogen cycle,"
said Schvarcz. "The cultures are also valuable as model systems for
studying symbiosis." These species illustrate how much we can still
learn from the ocean.

As co-author and UHM professor Angelicque White put it, "This work is
a reminder of the incredible diversity of the oceans and that they are
still a place for discovery of new life and new metabolic strategies." ========================================================================== Story Source: Materials provided
by University_of_Hawaii_at_Manoa. Original written by Marcie
Grabowski. Note: Content may be edited for style and length.


========================================================================== Related Multimedia:
* One_of_the_new_diatom_species,_Epithemia_pelagica ========================================================================== Journal Reference:
1. Christopher R. Schvarcz, Samuel T. Wilson, Mathieu Caffin, Rosalina
Stancheva, Qian Li, Kendra A. Turk-Kubo, Angelicque E. White,
David M.

Karl, Jonathan P. Zehr, Grieg F. Steward. Overlooked and
widespread pennate diatom-diazotroph symbioses in the sea. Nature
Communications, 2022; 13 (1) DOI: 10.1038/s41467-022-28065-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220211102719.htm

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