Eating fish — without the fear of mercury

If you love seafood but worry about the effects of mercury, UCLA has good news. New research by university scientists and colleagues suggests that a specially engineered probiotic could one day help your body block toxic mercury before it causes harm — without forcing you to give up your favorite sushi dish.

It’s particularly welcome news for pregnant women — toxic mercury has been shown to pose a serious threat to the developing fetus — as well as those who subsist on a largely fish-based diet.

So what’s the connection between fish and mercury? Methylmercury, a highly toxic form of mercury, forms when environmental mercury — released primarily by human activities like coal burning, artisanal gold mining, smelting and industrial waste — makes its way into bodies of water. This contaminant then increases in concentration as it moves up the marine food chain. Larger predators like bluefin tuna — and later, the humans consuming the fish — acquire all the mercury accumulated by the previous links in the chain. People who eat food with high mercury levels are at greater risk of mercury poisoning and birth defects.

With funding from the National Science Foundation and other sources, scientists from UCLA and UC San Diego’s Scripps Institution of Oceanography engineered a common human gut bacterium by inserting genes that encode methylmercury‐detoxifying enzymes. They then administered the microbe as a probiotic to mice that had been fed a diet rich in bluefin tuna. They found that the microbe detoxified methylmercury in the guts of the mice and dramatically reduced the amount of the contaminant that reached other tissues, such as the brain and liver.

Importantly, pregnant mice and their fetuses displayed significantly reduced methylmercury accumulation and lower signs of brain toxicity, pointing to potential benefits for maternal and fetal health.

While the findings are still in early stages, the researchers are optimistic. With continued funding and development, they plan to improve the probiotic’s effectiveness and ensure it can be safely translated for human use with continued funding and development.

The study’s senior author, Elaine Hsiao, an associate professor and director of the UCLA Goodman–Luskin Microbiome Center, envisions the possibility that one day people will simply be able to take a probiotic pill that will offset the risk of too much mercury — preserving the benefits of fish consumption in diets around the world and protecting pregnant women from harm.