We’re Consuming More Mercury Linked to Fish. Scientists Are Fighting Back With Engineered Probiotics

Mercury in fish is an escalating food safety concern. Prolonged exposure to this toxic metal poses serious health risks, and experts warn that the problem is likely to get worse before it gets better.

A real detox. To combat this issue, researchers have engineered a strain of gut bacteria capable of breaking down methylmercury—the most toxic form of mercury commonly found in seafood. In mice, the modified bacteria effectively trapped the compound in the digestive system, preventing it from reaching critical organs like the brain and liver.

The growing threat. Methylmercury is a positively charged organic form of mercury that accumulates in fish through a process called biomagnification.

As mercury from industrial emissions enters the oceans, it moves up the food chain and becomes more concentrated in larger, predatory fish—the same ones often found in human diets.

Enter the designer bacteria. The research team started with Bacteroides thetaiotaomicron, a common microbe found in the human gut. They inserted genes from a soil-dwelling bacterium known for its mercury resistance, giving the modified strain the tools needed to neutralize methylmercury.

Probiotics. After confirming in vitro that the modified bacteria could resist and process methylmercury, researchers administered them to mice. Once established in the gut, the bacteria significantly reduced mercury absorption.

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The researchers first assessed the impact of administering a high dose of methylmercury. In mice that received the engineered bacteria, mercury began clearing from their systems within hours, with the detoxification process continuing for about four days.

Long-term exposure. The team also evaluated the effects of sustained, moderate mercury intake by feeding the mice a diet rich in bluefin tuna—one of the fish with the highest levels of methylmercury. Remarkably, the bacteria continued to neutralize the toxin over time, preventing it from spreading beyond the digestive tract into other tissues.

The effects were especially notable in pregnant mice: methylmercury levels remained low in both maternal and fetal tissues, including the fetal brain, indicating reduced toxicity. The findings were published in Cell Host & Microbe.

A Band-Aid for a worsening problem. While the study doesn’t address the root cause of mercury pollution, it offers a promising workaround: engineered probiotics that could help limit the toxin’s impact on human health. According to the researchers, this approach won’t solve the broader environmental crisis—but it may provide critical protection against a threat with no short-term solution.

“Despite global efforts to reduce mercury emissions and its accumulation in fish, methylmercury levels in seafood are not expected to decline anytime soon. Fish remains a major and culturally important part of the diet for many people around the world, and we hope it continues to be,” coauthor Amina Schartup said.

Image | R Eris (Unsplash)

Related | We’ve Polluted the Oceans With Mercury for Centuries. Could Genetic Engineering Be the Solution?