Hacked bacteria could keep tabs on the health of your innards

THINK of them as tiny environmental health officers.  For the first time, bacteria have been engineered to monitor the state of a live animal’s gut. A team led by Pamela Silver at Harvard Medical School inserted genes from a virus into E.coli bacteria. Normally these genes make a protein called cI, but when the bacteria are exposed to a substance called anhydrotetracycline, they instead produce a protein called Cro. The team fed the bacteria to mice and collected faecal samples. Sure enough, only cI was detected unless the mice were given the chemical, in which case their faeces contained Cro proteins.  The addition of the viral genetic switch meant the bacteria was effectively sensing and recording the chemical’s presence. Silver says it should be easy  to engineer other genetic switches – ones that respond to telltale signs of inflammation, cancer, parasites or toxins in  the gut, for example (PNAS, DOI:10.1073/pnas.1321321111). “This is a really exciting advance,” says Chris Voigt of MIT’s Synthetic Biology Center. “It is remarkable that they were able  to engineer the cells to perform a computational operation, albeit a simple one, in this environment.” We might even be able to engineer bacteria that deliver drugs if they detect disease.  “You could think of them as little programmable robots that sense their environment and enact a therapeutic action when they discover a problem,” says Voight. Silver’s team is already exploring ways to do this.