Intestinal insects strip mercury from fish that are not sacrificial to blood

A groundbreaking study by UCLA and UC San Diego scientists found that newly designed intestinal bacteria could quickly make fish safer by neutralizing toxic mercury before entering the bloodstream.

Modified bacteria, strains Bacteroides thetaiotaomicron Methylmercury (a powerful neurotoxin found in seafood) commonly in the human intestine effectively dismantles the absorption and accumulation of important organs. Research published in Cell hosts and microorganismsdemonstrates that this microbial approach may be particularly beneficial for pregnant women who are concerned about mercury exposure affecting growing babies.

“The researchers are heading the goodman Ruskin Microbiohm Center at UCLA,” said Elaine Fuciao, associate professor at UCLA who oversees the research.

The researchers designed the bacteria by inserting two genes from mercury-resistant soil microorganisms found in contaminated mining areas. These genes produce enzymes that convert harmful methylmercury, which does not easily cross the bloodstream, into less harmful forms.

In clinical testing, engineered bacteria efficiently detoxified methylmercury from both pure solutions and actual fish tissues. When introduced into mice fed a diet containing mercury-rich bluefin tuna, the bacteria reduced intestinal mercury levels within just 3 hours.

More importantly, mice colonized with engineered bacteria showed significantly reduced mercury accumulation in maternal and fetal tissues during pregnancy.

“By reducing methylmercury in the intestinal diet, intestinal bacteria helped to enter the maternal bloodstream and eliminate it from the body before accessing its developing offspring,” explained Christie Yu, the study’s first author and UCLA research scientist.

This work addresses a permanent global health challenge. Despite international efforts to reduce mercury emissions since the 2013 Minamata Treaty, methylmercury continues to accumulate in seafood, particularly large predatory fish such as tuna and swordfish.

For many communities around the world, seafood represents the staples and cultural touchstones of an irreplaceable diet. “Fishes continue to be a major and culturally important part of diet for many people around the world, and we hope that continues,” says Amina Schartup, associate professor of marine biogeochemistry at the Institute of Oceanography.

In addition to simply lowering mercury levels, researchers also recorded meaningful biological benefits. Engineered bacteria reduced harmful genetic and cellular changes in fetal mouse brains exposed to dietary mercury. By examining brain tissue samples, they found that maternal colonization with modified bacteria protected against abnormal expression of genes associated with cell stress, protein translation, and cell cycle regulation, i.e., all typical mercury toxic markers.

This approach offers advantages over traditional chelation processes for metal poisoning, which indiscriminately binds many metals, including essential nutrients such as zinc and copper. The bacterial approach targets methylmercury without disrupting beneficial minerals.

Another researcher on the team, Francis Caschandra, emphasized that bacteria are effective even when fish species and mercury concentrations are different. “Bacteria were also effective when we repeated the experiments with salmon containing lower levels of methylmercury than bluefin tuna,” he said.

That makes this approach particularly promising B. THETAIOTAOMICRON Clinical safety trials have already been completed as a potential probiotic. Recent human trials of double-blind, placebo-controlled, demonstrated their safety and potentially accelerated the path to practical use.

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

Researchers warn that human research will remain integral to the next step, but they are beginning to optimize bacteria for greater effectiveness. This approach could ultimately provide a practical solution for individuals and communities who rely heavily on seafood consumption. This allows for the maintenance of dietary traditions while reducing associated health risks.

For billions who rely on fish as primary protein sources, this microbial innovation can ultimately alter risk calculations regarding seafood consumption, especially during pregnancy, where the brain is most vulnerable to toxic exposure.