Engineered Bacteria Measure Caffeine Concentrations

In a new study, a team of researchers have developed a unique way to measure caffeine levels. They’ve engineered Escherichia coli so that the bacteria’s growth depends on the concentration of the invigorating compound. High levels of caffeine can be toxic to some bacteria, but one species called Pseudomonas putida CBB5 has a multienzyme biochemical pathway that degrades the chemical into xanthine and formaldehyde. For a synthetic biology competition, a student team from the University of Texas, Austin, led by Jeffrey E. Barrick, wanted to transfer that caffeine degradation ability to E. coli. Making such a transfer is not simple, but E. coli is one of the more easy bacterial species to engineer. The team assembled an engineered genetic package, in part, from P. putida genes for the pathway. They then inserted the package into an E. coli strain unable to make guanine, a DNA base that is necessary for bacterial growth. If the genetic instructions worked, the genes would code for proteins that removed two methyl groups on caffeine to make xanthine, an intermediate in guanine biosynthesis. As a result, these engineered bacteria would only grow in the presence of caffeine. When the scientists added the bacteria to cultures supplemented with caffeinated sodas, espresso, or energy drinks, the microbes thrived. But nothing grew in cultures lacking the caffeinated beverages. The amount of bacterial growth also was proportional to the amount of caffeine in the culture. Using microbe growth, the researchers measured caffeine levels that mirrored reported values for those beverages. As caffeine biosensors, Barrick says these bacteria are accurate and simple enough for high school students to use.