The group of researchers, who hail from University of Texas at Austin and University of Iowa, Iowa City, engineered the E. coli bacteria to not only metabolize caffeine, they created a bacterial strain that can't live without it. (I know the feeling.) Due to a quirk in its metabolism, the bacteria cannot synthesize DNA or RNA without caffeine, providing a useful "kill switch" for when decaffeination is complete. To test their bacterias' abilities to metabolize caffeine and their relative addictedness to the compound, the researchers then grew the transfected E. coli on a variety of growth media containing caffeinated beverages, including Coca-Cola, Diet Coke, Starbucks Espresso, Monster and Red Bull (brave, brave E. coli). They also used caffeine-free Coca Cola in the growth media, and found that the bacteria simply could not survive without a jolt of joe. Most interestingly, the researchers found that they could back-calculate the amount of caffeine in a given sample by measuring how well the bacterial cells grew in that medium, making the bacteria a useful biomonitor as well as clean-up crew.