【Nat Communi】New field!

On February 11, 2022, the journal Nature Communications published a research paper titled "Overlooked and widespread pennate diatomdiazotroph symbioses in the sea" from Christopher R.
Schvarcz and others of the Daniel K.
Inouye Center for Microbial Oceanography in the United States
.

The study identified two new and unusual diatom species in Hawaiian waters that fix nitrogen
.

This is a previously overlooked but widespread source of bioavailable nitrogen in marine habitats and provides a new, easily culturable model organism for studying organelle evolution
.

Diatoms are one of the main planktonic algae in the ocean, the main provider of global primary productivity, and play an important role in the circulation of elements such as carbon and oxygen on the earth
.

Diatoms contain fucoxanthin, chlorophyll c, diacoxanthin and other photosynthetic pigments that are different from green photosynthetic organisms, so they have special light energy capture, energy transfer and photoprotection mechanisms
.

In the nutrient-poor open ocean around Hawaii, diatoms struggle to get enough nitrogen to grow
.

To address this issue, some diatoms have established symbiotic relationships with nitrogen-fixing cyanobacteria, such as the two most prominent types of marine nitrogen-fixing symbionts are the facultative association between heterocyst-forming cyanobacteria and central diatoms, and the unicellular cyanobacteria Association between bacteria and Dinoflagellate haptophytes
.

These types of symbionts are easy to spot under a microscope because the cyanobacteria that live in them fluoresce bright orange-yellow
.

The study added seawater samples to nitrogen-depleted growth media, and then discovered two new species under the microscope over a period of weeks and months
.

The two new diatom species isolated in this study are smaller and belong to different lineages, with elongated or "pinnate" shaped diatoms Epithemia pelagica sp.
nov.
and Epithemia catenata sp.
nov.
They are elongated or have bilateral symmetry The symbionts are also smaller, single-celled, and don't glow under fluorescent light because they don't contain chlorophyll, making them nearly invisible inside diatoms
.

They have similar nifH gene sequences to free-living unicellular cyanobacteria, and show that Epithemia symbionts are globally distributed in marine environments, illustrating that the symbionts are previously overlooked but widespread in marine habitats.
Utilize sources of nitrogen
.

Another surprise came when further studies measured the cultures' daily nitrogen fixation patterns
.

E.
pelagica and E.
catenata symbionts exhibit a unique daily pattern of N fixation
.

That is, nitrogen fixation begins in the dark around midnight and continues into the morning, afternoon and evening
.

Then rest for six hours at sunset
.

This new method of nitrogen fixation differs from previous discoveries that have only focused on day or night, and opens up many exciting avenues for further research
.

The work is a reminder of the amazing diversity of the oceans, which are still a place for discovering new life and new metabolic strategies
.

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