The salmon superfood you’ve never heard of

(Press-News.org) In northern California, salmon are more than just fish—they’re a cornerstone of tribal traditions, a driver of tourism and a sign of healthy rivers. So it may not come as a surprise that NAU and University of California Berkeley scientists working along the region’s Eel River have discovered a micro-scale nutrient factory that keeps rivers healthy and allows salmon to thrive.  

The scientists’ new study in Proceedings of the National Academy of Sciences (PNAS) reveals how a partnership between algae and bacteria works like nature’s clean-nitrogen machine, turning nitrogen from the air into food that fuels river ecosystems without fertilizers or pollution. The hidden nutrient factory boosts populations of aquatic insects, which young salmon rely on for growth and survival. 

At the heart of the scientists’ discovery is a type of diatom—a single-celled aquatic plant in a glass-like shell—called Epithemia. The golden-brown diatom, smaller than a grain of table salt and approximately the width of a human hair, plays a massive role in keeping rivers productive. Inside each diatom live bacterial partners housed within the cell called diazoplasts—tiny nitrogen-fixing compartments that transform air into plant food. The diatom Epithemia captures sunlight and makes sugar, which the diazoplast uses to turn atmospheric nitrogen into a nutrient form. In return, the diazoplast provides nitrogen that helps the diatom keep photosynthesizing. 

“This is nature’s version of a clean nutrient pipeline, from sunlight to fish, without the runoff that creates harmful algal blooms,” said Jane Marks, biology professor at Northern Arizona University and lead author of the study. 

By late summer, Marks said, strands of the green alga Cladophora are draped with rusty-red Epithemia along the Eel River. At this stage, the algae–bacteria duos supply up to 90% of the new nitrogen entering the river’s food web, giving insect grazers the fuel they need and powering salmon from the bottom up. 

“Healthy rivers don’t just happen—they’re maintained by ecological interactions, like this partnership,” said Mary Power, co-author of the study and faculty director of UC Berkeley’s Angelo Coast Range Reserve, where the field study took place. “When native species thrive in healthy food webs, rivers deliver clean water, wildlife and essential support for fishing and outdoor communities.” 

Using advanced imaging, the research team watched the partners trade life’s essentials in a perfect loop: The diatom used sunlight and carbon dioxide to make sugar and share it with the bacterium, which then used the sugar to turn nitrogen from the air into plant food. That nitrogen helped the diatom make even more sugar, because the key enzymes of photosynthesis need lots of nitrogen. 

“It’s like a handshake deal: Both sides benefit, and the entire river thrives,” said Mike Zampini, a postdoctoral researcher at NAU and the study’s isotope tracing lead. “The result is a beautifully efficient cycle of energy and nutrients.” 

This partnership isn’t unique to the Eel River. Epithemia and similar diatom–diazoplast teams live in rivers, lakes and oceans across the world, often in places where nitrogen is scarce. That means they may be quietly boosting productivity in many other ecosystems. 

Beyond its role in nature, this clean and efficient nutrient exchange could inspire new technologies such as more efficient biofuels, natural fertilizers that don’t pollute or even crop plants engineered to make their own nitrogen, cutting costs for farmers while reducing environmental impacts. 

When nature engineers solutions this elegant, Marks said, it reminds us what’s possible when people, places and discovery come together. 

Other researchers involved in the study included NAU faculty Bruce Hungate and Egbert Schwartz, staff members Michael Wulf and Victor Leshyk and graduate students Raina Fitzpatrick and Saeed Kariunga; University of Alabama professor Steven Thomas and graduate student Augustine Sitati; and Lawrence Livermore National Laboratory researchers Ty Samo, Peter Weber, Christina Ramon and Jennifer Pett-Ridge. The research was funded in part by a grant from the National Science Foundation’s Rules of Life/Microbiome program (#2125088). Research at Lawrence Livermore National Labs was conducted under U.S. Department of Energy Contract DE-AC52-07NA27344. 

END