IF ({x} AND {y}) THEN {phenotype}; Programming Bacterial Invasion

Anderson, Voigt and Arkin (UCSF and UC Berkeley) have teamed up to demonstrate the operation of an exquisitely-designed genetic AND gate to control the behavior of E coli (original paper here). The gate integrates two environmental inputs to produce a phenotypic output. As an example, they show how their circuit can be used to program bacteria to invade mammalian cells when the concentrations of two different extracellular chemicals fall within a certain range. You can bet Anderson will be using this circuit to fine tune the specificity of his tumor-invading bacteria in the future. For example:

IF ({hypoxia} AND {acid pH})
THEN
invade

Very nice tricks for making tumor-specific microorganisms. However based on our experience with ad hoc-engineered tumor-killing microbes, the biggest challenges will come in trying to deliver these agents in vivo.