Intestinal worms strip mercury from fish without blood donation

According to groundbreaking research by UCLA and UC San Diego, a newly designed gut bacteria may soon enter the bloodstream by neutralizing toxic mercury, making it safer.

Modify bacteria, a bacterial thetaiotaomicron Common in the human gut, the effective removal of methyl macre, a powerful neurotoxin found in seafood, reduces its absorption and accumulation in vital organs. The study, published in cell hosts and microorganisms, suggests that this microbial approach may particularly benefit pregnant women who are concerned about mercury exposure to their developmental babies.

“We envision people taking probiotics to offset the risk of eating too much methylmercury, especially when pregnant,” said Elaine Hsiao, associate professor at UCLA.

The team designed the bacteria by inserting two genes from mercury-containing soil microorganisms found in contaminated mining areas. The enzymes produced by these genes convert toxic methylmercury into smaller and harmful forms that do not easily penetrate the bloodstream.

In laboratory tests, the engineered bacteria effectively detoxify from pure solution and from actual fish tissue. When mice fed with mercury-rich bluefin tuna were introduced, the bacteria lowered the mercury levels in the intestinal tract in just three hours.

More importantly, mice settled with engineered bacteria significantly reduced mercury accumulation in maternal and fetal tissues during pregnancy, a critical period when methylmercury poses the greatest risk to nervous system development.

“By reducing methylmercury in the intestines, gut bacteria help eliminate it from the body before they can enter the maternal blood and enter the developmental offspring,” explains Kristie Yu, the first author of the study and a UCLA research scientist.

This work addresses ongoing global health challenges. Despite international efforts to reduce mercury emissions since the 2013 Minamata Conference, methylmacres are still accumulating in seafood, especially large predatory fish such as tuna and swordfish, which concentrate mercury from underneath everything in the food chain from everything under them.

For many communities around the world, seafood represents an irreplaceable dietary staple and cultural touchstone. “For many people in the world, fish remains a major and culturally important part of the diet,” said Amina Schartup, associate professor of marine biogeochemistry at the Scripps Institute of Oceanography.

In addition to simply reducing mercury levels, the researchers also documented meaningful biological benefits. Engineered bacteria reduce harmful genetic and cellular changes in the brains of fetal mice exposed to dietary mercury. By examining brain tissue samples, they found that maternal colonization with improved bacteria is protected from abnormal expression of genes (all typical markers of mercury toxicity) associated with cellular stress, protein translation, and cell cycle regulation.

This method provides an advantage over traditional metal poisoning, which indiscriminately combines many metals, including essential nutrients such as zinc and copper. Bacterial methods specifically target methyl substrates without destroying beneficial minerals.

Franciscus Chandra, another researcher on the team, stressed that bacteria are effective even with different fish types and mercury concentrations. “When we repeated the experiments with salmon, which contained lower methylmercury levels than bluefin tuna, the bacteria were also effective,” he said.

What makes this approach particularly promising is B. Thetaiotaomicron Clinical safety trials have been completed as potential probiotics. A recent double-blind, placebo-controlled human trial demonstrated its safety and potentially accelerate the path to practical applications.

The project has received support from several research institutions, including the National Institute of Environmental Health Sciences, the National Science Foundation and the Simmons Foundation.

Researchers warn that human research remains an important next step, but they have begun optimizing bacteria to improve their efficacy. This approach can ultimately provide a practical solution for individuals and communities who rely heavily on seafood consumption, allowing them to maintain their dietary traditions while reducing the associated health risks.

For billions of people who rely on fish as their primary source of protein, this microbial innovation may eventually change the risk calculations around seafood consumption, especially during pregnancy, when the brain in the developing brain is most susceptible to toxic exposure.