Microscopic caffeine fiends

Maybe you’ve heard coffee or cola drinkers say they’re “addicted” to caffeine. But a passion for this stimulant doesn’t compare to actually needing caffeine to survive and reproduce. Researchers recently transformed a germ into a true caffeine fiend. And when they were through, this bacterium had to consume caffeine — or die.

Its designers say their new microbe could be used to clean up waters tainted by caffeine. It also could help researchers measure the amount of caffeine in liquids.

The leaves, seeds and fruits of many plants contain caffeine. In coffee plants and tea bushes, caffeine acts as a natural pesticide. It will kill or harm insects that attempt to dine on the plant. Caffeine is also toxic to some types of plants, bacteria — even frogs. But several teams of scientists have discovered that some soil bacteria can perform a neat trick. These microbes can break down caffeine and then use a byproduct to make guanine, a nutrient they need to grow and thrive.

Guanine is one of four key substances cells use to make DNA (short for deoxyribonucleic acid). The long molecule instructs each cell on what it should do.

Jeffrey Barrick and his coworkers thought that they might be able to harness the soil bacterium’s caffeine-mining trick. A biochemist, Barrick studies the chemical activities inside living organisms at the University of Texas at Austin. But the scientists realized they couldn’t use the soil microbe itself because it doesn’t depend on caffeine for guanine. So they made a bacterium that did. They started by transplanting into it the genes that impart the caffeine-converting trick. And they used a microbe that wouldn’t be able to make guanine from any other source. So their novel microbe would absolutely depend upon caffeine for that guanine.

Their germ was a strain of Escherichia coli, better known as E. coli. (While some types of E. coli cause disease, Barrick and his team used a harmless type.)

When the genes they inserted didn’t work perfectly in this germ, Barrick’s group added more genes. That solved that problem. The scientists describe how they developed their designer microbe online March 8 in the journal Synthetic Biology.

The team’s work “was an interesting engineering project,” says Christopher Voigt. He’s a bioengineer at the Massachusetts Institute of Technology in Cambridge. (Engineers use science to design new products and processes; bioengineers tinker with biology in particular.) Indeed, Voigt can think of many ways the new caffeine-consuming bacterium might be used.

For instance, water treatment plants could use the germ to remove caffeine and caffeine-based drugs from sewage. Normal water treatment processes don’t remove caffeine, he notes. What’s more, using chemicals to remove pollutants that often occur in only tiny amounts can be very costly. The new bacteria, he says, might be a more affordable way to do that.

Someday, says Voigt, the same sort of techniques used to create the caffeine-consuming bacterium could be used to modify microbes that live in the human gut. Those bacteria might be engineered to more effectively break down certain compounds in foods, helping digestion. Or maybe, he suggests, they could even be designed to treat disease.

But for now, Barrick’s group has focused on a simpler problem. They use their designer E. coli to measure how much caffeine is in soft drinks and other beverages. Barrick puts some of the germs in a small amount of the beverage — 2 milliliters, for example. Then he lets the bacteria multiply until they run out of caffeine. His team then counts the microbes in the liquid. The researchers use that number to estimate how much caffeine had originally been in the drink.

Another potential use: eliminating caffeine from leftovers generated by coffee producers. Many of those byproducts are rich in nutrients. Once the caffeine was removed, they could be used as fertilizers or animal feeds, Barrick says.

Power Words

biochemist A scientist who studies the chemical processes and chemical transformations that take place inside organisms.

bioengineer A scientist who uses the principles of biology and the techniques of engineering to design organisms or products that can mimic, replace or augment the chemical or physical processes present in existing organisms. This field includes researchers who genetically modify organisms, including microbes. It also includes researchers who design medical devices such as artificial hearts and artificial limbs.

DNA Short for deoxyribonucleic acid, DNA is the large molecule that cells use to store the genetic information they need to live and reproduce.

E. coli A microorganism that researchers often use to study genetics. Some types of Escherichia coli cause disease, but many other types do not.

gene A segment of DNA associated with a particular trait that can be passed on to an organism’s offspring. (While some of these traits are visible, such as eye and hair color, others such as blood type and increased risk for specific diseases are not.) Genes also hold the information an organism needs to build and maintain its cells.

genetic engineering The direct manipulation of an organism’s genome. In this process, genes can be removed, disabled so that they no longer function, or added after being taken from other organisms. Genetic engineering can be used to create organisms that produce medicines, or crops that grow better under challenging conditions such as dry weather, hot temperatures or salty soils.

guanine One of four substances that organisms need to produce DNA.

stimulant A substance that causes temporary improvements in either mental or physical function or both. Caffeine is a mild stimulant that for a short while enhances alertness and helps fight drowsiness. Other stimulants, including some drugs, have stronger or longer-lasting effects.