The salmon superfood you’ve never heard of

Northern Arizona University

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Illustration by Victor Leshyk

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Credit: Victor Leshyk/Northern Arizona University

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. 

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2503108122 

Subject of Research

Not applicable

Article Title

Ecosystem consequences of a nitrogen-fixing proto-organelle

Article Publication Date

8-Sep-2025

 

Duke-NUS study reveals how dengue rewires the immune system, reshaping vaccine response

Research helps explain why vaccines work better for people with prior infection and why even an imperfect vaccine can be used safely to prevent dengue

Duke-NUS Medical School

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Dengue-infected cells taken under a microscope

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Credit: Summer Zhang, Duke-NUS Medical School

SINGAPORE, 8 SEPTEMBER 2025—Just as a computer’s operating system can be rewritten after a major update, dengue infection can ‘re-programme’ the body’s immune system, leaving a long-lasting genetic imprint that influences how people respond to future infections—an effect not seen with vaccination.

These novel insights from a recent study shed light on the mechanics of dengue disease progression and vaccine action, filling an important knowledge gap on how even imperfect vaccines can be used safely. It also paves the way for the future development of safer and more effective dengue vaccines. The research was published in the journal Med, by scientists at Duke-NUS Medical School in collaboration with an international team of researchers.

Dengue is a mosquito-borne virus that affects millions of people in tropical and subtropical regions each year. The illness can range from a mild fever with rash to a severe, life-threatening disease involving bleeding and organ failure. As there are four different types of dengue viruses, everyone is theoretically vulnerable to being infected up to four different times in a lifetime.

Currently, dengue vaccines have limitations—they are more effective in preventing the disease in people who have been infected with dengue previously. In such individuals, vaccination protects against illness from all four types of dengue viruses. The conventional thinking is that vaccination activates memory immune cells generated from prior dengue virus infection, to boost protection against the remaining types of dengue viruses. Without such pre-existing immune cells, the quality of the immune response to vaccination is thought to be poorer.

On these grounds, vaccines that have been approved by the World Health Organization require more than one dose. Theoretically, the first dose should generate immune cells resembling those formed following a previous dengue infection. The second vaccine dose would then activate these cells to enhance protection against dengue. However, the immune response to the second dose is still lower than in those with prior infection with just one dose.

To understand how the immune response to vaccination is different from that of natural dengue virus infection, the researchers conducted a clinical trial involving 26 volunteers in the US from 2018 to 2020. Participants received two doses of a dengue vaccine[1], administered 90 days apart. The team then analysed and compared blood samples from those volunteers who had previously been infected with dengue with those who had not. To ensure wider representation, around 50 volunteers from Singapore with no recent dengue virus infection also contributed blood samples to be analysed from 2022 to 2023.

The team discovered that even before being vaccinated, those with prior dengue infection already showed distinct patterns of gene activity. Surprisingly, these gene activity patterns were not found in the memory cells that produce antibodies, but in specific types of immune cells that the dengue virus infects.

Dr Eugenia Ong, Principal Research Scientist from the Emerging Infectious Diseases Programme at Duke-NUS Medical School and first author of the study, explained:

“Our findings show that natural dengue infection can leave a lasting genetic imprint on the immune system. Instead of returning to normal, the immune system resets into a new baseline—one that may explain why second infections are often more severe.”

Because of this new baseline, the scientists found that in those who had been infected with dengue previously, the first dose of the vaccine triggered a stronger immune response than in those without a previous dengue infection. As vaccination, unlike natural infection, does not leave an imprint, the immune response in those without prior dengue virus infection remain lower than in those with prior dengue, even with two doses of the vaccine.  

This long-term imprinting, also known as trained immunity, has been observed in other infections, like malaria, and after certain vaccines, such as BCG. This study adds dengue to that list and shows that both the type and intensity of infection matter.

Professor Ooi Eng Eong from the Emerging Infectious Diseases Programme at Duke-NUS Medical School and senior author of the study, explained:

“Think of it as training for a sport—the immune system only gets a real workout from the full game—the equivalent of a natural infection. A light warm-up from vaccination isn’t enough to reprogramme it. This reveals a threshold of immune response needed to leave an imprint on the immune system.”

A particular set of imprint that the researchers found involved genes that normally trigger immediate antiviral response to infection. These genes were less active in those with prior dengue infection. The dampened response means that upon vaccination (which uses a weakened viral strain), the resulting infection generates high levels of antibodies against the dengue virus. However, the dampened antiviral response may also explain why a second dengue infection with another dengue virus strain, often carries a higher risk of progressing to severe illness.

Professor Patrick Tan, Senior Vice-Dean for Research at Duke-NUS Medical School, said:

“As dengue continues to affect millions across Asia, Latin America and other tropical regions, this study closes a critical gap in our understanding of how infection reshapes the immune system. These insights are vital not only for developing better vaccines but also for guiding global and national health policies. At Duke-NUS, our goal is to ensure that discoveries like these translate into real protection for the communities most at risk.”

The team hopes their work will encourage more research into the long-term effects of immune reprogramming and its impact on responses to other infections and vaccines. They also hope that this new evidence would shape advocacy and global health policies on dengue vaccines that have been approved or are close to being approved. The scientists feel it is unlikely that a perfect dengue vaccine would be developed in the next 10 years—current vaccines, although imperfect, can still be used safety to reduce the estimated 100 million cases of dengue globally each year.

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DOI: 10.1016/j.medj.2025.100841

 

About Duke-NUS Medical School                 

Duke-NUS is Singapore’s flagship graduate entry medical school, established in 2005 with a strategic, government-led partnership between two world-class institutions: Duke University School of Medicine and the National University of Singapore (NUS). Through an innovative curriculum, students at Duke-NUS are nurtured to become multi-faceted ‘Clinicians Plus’ poised to steer the healthcare and biomedical ecosystem in Singapore and beyond. A leader in ground-breaking research and translational innovation, Duke-NUS has gained international renown through its five Signature Research Programmes and ten Centres. The enduring impact of its discoveries is amplified by its successful Academic Medicine partnership with Singapore Health Services (SingHealth), Singapore’s largest healthcare group. This strategic alliance has led to the creation of 15 Academic Clinical Programmes, which harness multi-disciplinary research and education to transform medicine and improve lives.   

For more information, please visit www.duke-nus.edu.sg 

 

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[1] TAK-003

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Journal

Med

DOI

10.1016/j.medj.2025.100841 

Method of Research

Randomized controlled/clinical trial

Subject of Research

Cells

Article Title

Dengue virus infection reprograms baseline innate immune gene expression

Article Publication Date

8-Sep-2025

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A new bystander effect? MALE Aggression can be contagious when observing it in peers.

Male mice become aggressive after watching peers—not strangers—attack intruders, and researchers have found a neural mechanism for this socially transmitted behavior.

Society for Neuroscience

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A depiction of the paradigm used to assess whether witnessing familiar peers or unfamiliar strangers fight for 10 min leads to aggression 30 min later. Only after watching familiar peers attack do male mice display aggression themselves, which is mediated by activation of medial amygdala neurons.

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Credit: Jacob Nordman via BioRender.

People who repeatedly observe aggression have a higher likelihood of engaging in violent behavior later in life. In a new JNeurosci paper, Jacob Nordman and colleagues, from Southern University of Illinois School of Medicine, used mice to explore the environmental factors and neural mechanisms that lead to the aggression that witnesses later acquire. 

In a behavioral paradigm created by this research group, mice observed known peers or unfamiliar strangers attack intruder mice. Only male witnesses later displayed increased aggression themselves, and this happened only after watching familiar peers attack intruders. 

What neural mechanism might be driving this behavior in the bystander males? As male mice behaved in the paradigm, the researchers recorded activity from neurons in a part of the amygdala that is implicated in aggression priming. Elaborating on this, says Nordman, “We previously found that these neurons are involved in an ‘aggression priming’ effect, meaning that being a perpetrator of an attack increases the likelihood of attacking again. For example, imagine getting in an argument with a coworker or family member. Afterwords, your agitation and frustration make you more likely to have another outburst.” The researchers theorized that these neurons might be active in male witnesses observing violent peers because the familiarity makes them mirror their friends’ own aggression priming. Indeed, these neurons were active in males as they saw familiar—but not unfamiliar—attacks. Notably, artificially inhibiting these neurons suppressed later aggression after witnessing peers, and activating these neurons while males watched violent strangers promoted attacking behavior in observers later.  

These findings shed light on aggression learned via observation, suggesting that not only proximity, but also familiarity of attackers may be risk factors for behaving violently later, at least in males. According to the authors, this neural mechanism could inform the development of neural and behavioral treatment interventions for learned violence. 

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Please contact media@sfn.org for full-text PDF. 

About JNeurosci 

JNeurosci was launched in 1981 as a means to communicate the findings of the highest quality neuroscience research to the growing field. Today, the journal remains committed to publishing cutting-edge neuroscience that will have an immediate and lasting scientific impact, while responding to authors' changing publishing needs, representing breadth of the field and diversity in authorship. 

About The Society for Neuroscience 

The Society for Neuroscience is the world's largest organization of scientists and physicians devoted to understanding the brain and nervous system. The nonprofit organization, founded in 1969, now has nearly 35,000 members in more than 95 countries. 

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Journal

JNeurosci

DOI

10.1523/JNEUROSCI.1018-25.2025 

Article Title

Familiarity Gates Socially Transmitted Aggression Via the Medial Amygdala

Article Publication Date

8-Sep-2025

 

New and simple detection method for nanoplastics.

Researchers at the University of Stuttgart have developed an “optical sieve” for detecting tiny nanoplastic particles. It works like a test strip and is intended to serve as a new analysis tool in environmental and health research.

Peer-Reviewed Publication

Universitaet Stuttgart

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Nanoplastic particles made visible: the newly developed test strip from the University of Stuttgart allows dangerous nanoplastic particles to be detected under a light microscope.

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Credit: University of Stuttgart / 4th Physics Institute

A joint team from the University of Stuttgart in Germany and the University of Melbourne in Australia has developed a new method for the straightforward analysis of tiny nanoplastic particles in environmental samples. One needs only an ordinary optical microscope and a newly developed test strip—the optical sieve. The research results have now been published in “Nature Photonics” (doi: 10.1038/s41566-025-01733-x).

“The test strip can serve as a simple analysis tool in environmental and health research,” explains Prof. Harald Giessen, Head of the 4th Physics Institute of the University of Stuttgart. “In the near future, we will be working toward analyzing nanoplastic concentrations directly on site. But our new method could also be used to test blood or tissue for nanoplastic particles.”

Nanoplastics as a danger to humans and the environment

Plastic waste is one of the central and acute global problems of the 21st century. It not only pollutes oceans, rivers, and beaches but has also been detected in living organisms in the form of microplastics. Until now, environmental scientists have focused their attention on larger plastic residues. However, it has been known for some time that an even greater danger may be on the horizon: nanoplastic particles. These tiny particles are much smaller than a human hair and are created through the breakdown of larger plastic particles. They cannot be seen with the naked eye. These particles in the sub-micrometer range can also easily cross organic barriers such as the skin or the blood-brain barrier.

Color changes make tiny particles visible

Because of the small particle size, their detection poses a particular challenge. As a result, there are not only gaps in our understanding of how particles affect organisms but also a lack of rapid and reliable detection methods. In collaboration with a research group from Melbourne in Australia, researchers at the University of Stuttgart have now developed a novel method that can quickly and affordably detect such small particles. Color changes on a special test strip make nanoplastics visible in an optical microscope and allow researchers to count the number of particles and determine their size. “Compared with conventional and widely used methods such as scanning electron microscopy, the new method is considerably less expensive, does not require trained personnel to operate, and reduces the time required for detailed analysis,” explains Dr. Mario Hentschel, Head of the Microstructure Laboratory at the 4th Physics Institute.

Optical sieve instead of expensive electron microscope

The “optical sieve” uses resonance effects in small holes to make the nanoplastic particles visible. A study on optical effects in such holes was first published by the research group at the University of Stuttgart in 2023. The process is based on tiny depressions, known as Mie voids, which are edged into a semiconductor substrate. Depending on their diameter and depth, the holes interact characteristically with the incident light. This results in a bright color reflection that can be seen in an optical microscope. If a particle falls into one of the indentations, its color changes noticeably. One can therefore infer from the changing color whether a particle is present in the void.

“The test strip works like a classic sieve,” explains Dominik Ludescher, PhD student and first author of the publication in “Nature Photonics”. Particles ranging from 0.2 to 1 µm can thus be examined without difficulty. “The particles are filtered out of the liquid using the sieve in which the size and depth of the holes can be adapted to the nanoplastic particles, and subsequently by the resulting color change can be detected. This allows us to determine whether the voids are filled or empty.”

Number, size, and size distribution of particles can be determined

The novel detection method used can do even more. If the sieve is provided with voids of different sizes, only one particle of a suitable size will collect in each hole. “If a particle is too large, it won’t fit into the void and will be simply flushed away during the cleaning process,” says Ludescher. “If a particle is too small, it will adhere poorly to the well and will be washed away during cleaning.” In this way, the test strips can be adapted so that the size and number of particles in each individual hole can be determined from the reflected color.

Synthesized environmental samples examined

For their measurements, the researchers used spherical particles of various diameters. These are available in aequous solutions with specific nanoparticle. Because real samples from bodies of water with known nanoparticle concentrations are not yet available, the team produced a suitable sample themselves. The researchers used a water sample from a lake that contained a mixture of sand and other organic components and added spherical particles in known quantities. The concentration of plastic particles was 150 µg/ml. The number and size distribution of the nanoplastic particles was also be determined for this sample using the “optical sieve”.

Can be used like a test strip

“In the long term, the optical sieve will be used as a simple analysis tool in environmental and health research. The technology could serve as a mobile test strip that would provide information on the content of nanoplastics in water or soil directly on site,” explains Hentschel. The team is now planning experiments with nanoplastic particles that are not spherical. The researchers also plan to investigate whether the process can be used to distinguish between particles of different plastics. They are also particularly interested in collaborating with research groups that have specific expertise in processing real samples from bodies of water.

The optical sieve nanoplastic particles fall into holes of the appropriate size in the test strip. The color of the holes changes. The new color provides information about the size and number of particles.

Credit

University of Stuttgart / 4th Physics Institute

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Journal

Nature Photonics

DOI

10.1038/s41566-025-01733-x 

Article Title

Optical sieve for nanoplastic detection, sizing and counting

Article Publication Date

8-Sep-2025