New probiotic could make it safer to eat seafood

While eating fish is a healthy choice for many, it can also expose people to methylmercury – a toxic form of mercury that builds up in the body and can harm the brain, liver, and developing babies in the womb. Now, scientists may have found a way to help the body eliminate it.

In a collaborative effort, scientists from the University of California, Los Angeles (UCLA) and the University of California, San Diego’s Scripps Institution of Oceanography created a specialized gut bacterium designed to neutralize methylmercury before it spreads through the body.

This tiny engineered microbe, once ingested, reduced the amount of mercury reaching the brain, liver, and even fetuses in pregnant mice.

Probiotic for fish consumption

The research team used Bacteroides thetaiotaomicron, a bacterium already living in the human gut, and enhanced it with DNA from a mercury-resistant soil microbe.

This inserted DNA encodes enzymes that can detoxify methylmercury. First, they tested the bacteria in lab dishes. Then, they introduced it into the digestive systems of mice whose natural gut microbes had been removed.

After giving these mice a large dose of methylmercury, they saw a noticeable drop in intestinal mercury levels in just three hours. Levels continued to fall for four days.

Next, the scientists fed the mice a diet rich in bluefin tuna – one of the fish highest in methylmercury. Even with this regular dietary exposure, the engineered bacteria kept working. Mercury levels dropped not only in the intestines but also in the brain and liver.

Protective effect against mercury

The team then moved on to pregnant mice. The results were promising. Methylmercury levels were lower in both the mothers and their developing fetuses. There were also fewer signs of damage in the fetal brains.

“By reducing dietary methylmercury in the intestine, the gut bacteria helped to eliminate it from the body before it could enter the maternal bloodstream and access the developing offspring,” said first author and UCLA research scientist Kristie Yu.

According to UCLA researcher Franciscus Chandra, the lowered signs of toxicity in the fetal brain showed that the bacterium works at levels that are biologically meaningful.

Probiotic offsets risks of eating fish

The team also tested the bacteria with salmon, a fish that has less methylmercury than tuna, and the probiotic still worked effectively.

Finally, the researchers gave the probiotic to mice that still had their normal gut microbes intact. These mice, fed the same bluefin tuna diet, also showed significantly reduced mercury in their tissues. This confirmed that the probiotic could work without replacing the natural gut microbiome.

“We envision the possibility that people could take a probiotic to offset the risk of consuming too much methylmercury, especially when pregnant,” said Elaine Hsiao, director of the UCLA Goodman-Luskin Microbiome Center.

Mercury and the food chain

Mercury pollution comes mainly from human activities like coal burning, gold mining, and industrial waste.

In the ocean, it turns into methylmercury – a form that is especially toxic and accumulates in the food chain. That means top predators like tuna – and the humans who eat them – end up with the highest concentrations.

Amina Schartup is the co-senior author of the study and a Scripps associate professor of marine biogeochemistry.

“Despite global efforts to reduce mercury emissions and its accumulation in fish, methylmercury levels in seafood are not expected to decline anytime soon,” said Schartup.

“Fish remains a major and culturally important part of the diet for many people around the world and we hope it continues to be.”

A step closer to consumer probiotics

The scientists are now working to make the probiotic even more effective. They’re also preparing for the long road toward making it available for humans.

Continued funding will be crucial to move this idea from mouse models to real-world solutions.

The research was supported by federal and private organizations, including the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the National Institute of Environmental Health Sciences, the National Science Foundation, and several foundations.

The full study was published in the journal Cell Host & Microbe.

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