Engineering Edible Bacteria

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The Caltech team focused on microbes in the gut, aiming to create a microbial solution to lactose intolerance. "Rather than taking a daily vitamin, you could drink some gut microbes and be set for a week or month or however long the microbes last," says Josh Michener, a Caltech graduate student who advises the team.

People who can tolerate dairy naturally secrete lactase, an enzyme that breaks down lactose, a sugar in milk. The breakdown products, which include glucose, are then absorbed into the blood from the small intestine. In people who are lactose intolerant, the sugar is passed to the large intestine, where it is eventually metabolized by a chain of bacteria. In the process, the microbes produce hydrogen and methane gas, the culprits behind the troublesome symptoms--nausea, bloating, gas, and diarrhea--of the disorder.

Lactase pills are available to help people digest milk products, but the Caltech students wanted a more permanent solution. They started with a strain of E. coli often used as a probiotic in Germany. The strain, called Nissle 1917, was originally extracted from soldiers in World War I who were immune to an extreme gastrointestinal virus that swept through an army camp, says Michener.

The students added three biological parts to the Nissle bacterium: a gene that produces the lactase enzyme, a receptor that recognizes lactose, and a sensor that causes the cell to break open at a certain concentration of lactose. With this system, bacteria in the gut would constantly produce lactase. When the receptors on a bacterium's outer surface bound to a sufficient amount of lactose, they would trigger the explosion of the cell, releasing lactase into the intestine to break down the sugar. The students have so far created the first two components but are having trouble designing the microbes to self-destruct in the proper manner. The team is also working on an edible microbe that would produce folate, a vitamin important for preventing birth defects.

Both teams presented their research at the iGEM competition at MIT this weekend, along with more than 70 other teams from universities around the globe. In past years, students have created everything from bacterial photographic film to banana-scented bacteria and tiny boxes made of DNA.