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November 8, 2004
Naturally decaffeinated coffee? Study holds promise
BY Beverly Clark
Researchers at Emory have made an important advancement in harnessing the ability of bacteria to make new molecules; their discovery could eventually lead to the creation of naturally decaffeinated coffee plants. The research, by Assistant Professor Justin Gallivan in chemistry and graduate student Shawn Desai, appeared in the Oct. 27 edition of the Journal of the American Chemical Society.
Bacteria are “terrific chemists,” Gallivan said, but they normally synthesize only molecules they need for their own survival. His research team hopes to make bacteria synthesize molecules they otherwise would not make on their own, with results that may someday benefit humans. Gallivan’s team reasoned that if a bacterium needs a particular molecule to survive, it has a strong incentive to help make it, so the goal was to make bacteria depend on a molecule they wouldn’t normally need.
In their first major breakthrough, the researchers coupled the life of a bacterium to the presence of theophylline, a compound used to treat asthma and produced by the breakdown of caffeine in both coffee and tea plants. One reason coffee has a high level of caffeine is that, in coffee plants, caffeine is synthesized very quickly but breaks down to theophylline very slowly.
“We know there is an enzyme that breaks caffeine down into theophylline, but we don’t know much about it,” Gallivan said. “We do know it works very slowly. Ideally we would like to speed it up a bit so we could create coffee plants that are low in caffeine. That’s where the bacteria come in—they now need the breakdown product of the enzyme (theophylline) for survival, but they can’t do much with caffeine.”
Gallivan explained that the idea is to supply these bacteria with caffeine, and give each bacterium a piece of DNA from coffee plants, hoping to encode the enzyme that will allow the bacterium to convert caffeine to the theophylline it needs to survive.
“At the end of the day, we will know that all of the surviving bacteria have ‘learned’ to convert caffeine to theophylline, and thus have the enzyme we’re interested in. We can then learn about the enzyme and how it works,” Gallivan said. “We hope to use a process known as ‘directed evolution’ to help speed up the enzyme to break down caffeine faster. Since the bacteria need theophylline for their survival, they’re partners
in the whole process.”
Eventually, he continued, the faster enzyme could be introduced into coffee plants to produce naturally decaffeinated coffee.
To develop bacteria that are addicted to theophylline, Gallivan and Desai used a piece of RNA called an “aptamer,” which is known to bind tightly to theophylline. The remaining challenge was to couple this bond to a vital function of the bacteria: the production of a protein. To do this, the Emory team created a new sequence of RNA known as a “riboswitch.”
In bacteria, riboswitches normally recognize essential molecules, such as vitamin B12, and switch the production of proteins on or off. Gallivan’s team created a synthetic riboswitch that recognizes theophylline and turns on the production of a protein (known as “cat”) that allows the cells to survive in the presence of an antibiotic known as chloramphenicol.
Most bacteria die when exposed to chloramphenicol, however bacteria containing the synthetic riboswitch survive—as long as theophylline is present, because theophylline turns on the production of the “cat” protein. And thus are created theophylline-dependent bacteria.
But Gallivan said not to expect good-tasting, naturally decaffeinated coffee anytime soon. “We’re still at the earliest stages of this work; there are many hurdles to overcome,” he said. “As a scientist, I’m excited about the future. As a caffeinated coffee addict, part of me is not in a hurry to solve this one.”