Experimental probiotic could detoxify mercury from diet

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An experimental probiotic could help detoxify mercury, which often contaminates fish, in the gut. Image credit: Courtney Rust/Stocksy.
  • Mercury from the environment can enter the food chain and cause health problems for humans, especially for developing fetuses and children.
  • Mercury is more absorbable in the intestine in some forms than others.
  • Recently researchers have developed a probiotic bacterium engineered to express an enzyme that converts more absorbable forms of mercury into less absorbable forms.
  • They hope this could eventually be used to minimize mercury exposure in humans, particularly in vulnerable populations.

Heavy metals are required for cellular functions in both humans and animals microorganisms found in their microbiomes. These heavy metals required by humans include copper, iron, cobalt, copper, manganese, molybdenum and zinc.

However, overexposure to some of these metals it can cause toxicity leading to health problems. Conversely, the difficulty of absorbing one of these iron metals through the intestine is linked to anemia, which the World Health Organization (WHO) estimates affect nearly a third of women globally.

Another heavy metal that can be absorbed by the human body is mercury. Mercury can be absorbed into humans through the skin from cosmetics such as lightening products that are banned in several countries February 2023 and also through the intestines.

Mercury exists in several forms, but it is methylmercury, formed by the action of bacteria on naturally occurring mercury in the environment, that can be absorbed by the human intestine. It is this form that poses a particular threat to fetal and infant neurodevelopment.

Populations that eat large amounts of fish are particularly affected by the health impacts of mercury, according to the WHO.

A well-known example of this occurred when a factory dumped methylmercury-containing chemical waste into the sea in Minamata, Japan between 1932 and 1968. At least 50,000 people are thought to have been affected by a condition known as Minamata disease, caused by excessive consumption of mercury from locally caught fish.

While bacteria are able to convert environmental mercury into methylmercury that can be absorbed by the intestines, there are also some enzymes that can convert methylmercury into forms that the intestines are less able to absorb.

These enzymes have been the focus of recent research conducted by a team from Pennsylvania State University. The team aims to develop a probiotic bacterium that can colonize the gut and ensure that this enzyme is released there.

The researchers presented the results of their study at ASM Microbe 2023, the annual meeting of the American Society for Microbiology held June 15-19, 2023 in Houston, Texas.

Led by doctoral researcher Daniela Betancurt, the team studied the enzyme organomercurial lyase, an enzyme that demethylates methylmercury, making it less absorbable.

The researchers initially used existing libraries of genomes of microorganisms found in the human gut microbiome to identify a gene for the enzyme organomercurial lyase.

However, they found that genes involved in mercury biotransformation were rare.

To determine which types of bacteria were most likely to express enzymes that would demethylate mercury, they exposed fecal samples from human donors to methylmercury and observed how this changed the composition of the microbiome present.

They found differences between individuals that correlated with the amount of metal resist me which indicate the ability of the bacteria to process the metals expressed by the bacteria in the gut. They conducted similar experiments on mice.

Finally, they identified a gene in a methylmercury-resistant strain of non-pathogenic bacteria Bacillus megaterium which codes for organomercurial lyase and inserted it into the probiotic bacterial strain Lacticaseibacillus.

Explained the lead researcher Betancurt Medical News Today in an email:

We inserted a gene from Bacillus megaterium a bacterium isolated from an industrial disaster at Minimata Bay in Japan. The gene provides the ability to convert methylmercury into poorly absorbed forms.

The study authors say they have confirmed that the presence of this strain demethylated mercury, making it inorganic and removable from the body. However, the research has not yet been published in a peer-reviewed journal.

Betancurt said the next step for the research was to conduct experiments in mice to help us quantify the bacteria’s effectiveness and examine its effects in the gut when the host is orally exposed to mercury.

We are also investigating other metals as well [are] interested in understanding how the microbial community reacts to different metals, she told us.

There is already a precedent for Lactobacilli to improve iron absorption, and we hope to look into this in more detail in the next work, Betancurt said.

Dr. Kelly Johnson-Arbor, medical toxicologist, medical co-director and interim executive director of the National Capital Poison Center, Washington, DC said MNT extension: There are several different forms of mercury found on Earth. Elemental mercury, or mercury, is a metal that exists as a liquid at room temperature. Inorganic and organic mercury also occur naturally in the environment in soil and air.

He explained that what is of concern is mercury’s high potential to contaminate commonly eaten foods:

Because mercury exists naturally in the environment, it can be incorporated into the food chain in the human diet. In aquatic environments, inorganic mercury can be converted to organic methylmercury and can bioaccumulate throughout the food chain. Larger fish, including tuna, swordfish and marlin, generally contain higher levels of methylmercury than smaller fish, due to mercury bioaccumulation.

Dr. Shilpa Dang, a gastroenterologist at Doctors Offices of Manhattan, NY, and double board certified by the American Board of Internal Medicine and the American Board of Gastroenterology explained to MNT extension how this can affect the human body.

He said: Mercury can interfere with numerous cellular processes, which can impair the normal functioning of the nervous system. Mercury can enter neurons in the brain, reducing their efficiency as transmitters of signals. It can also damage the protective coating of nerve fibers, known as myelin, which disrupts communication between nerve cells.

Multiple health problems, especially those affecting the neurological system, can result from exposure to mercury. It can cause problems with a child’s cognitive development, language development, and motor development. Adults who are exposed to excessive levels of mercury can experience memory loss, concentration problems and physical weakness, Dr. Dang noted.

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