DOI
0.1038/nature02298

Summary
The activation of the Lac operon in E. coli and its repression by glucose has been studied with two engineered strains able to show the induction level by means of green fluorescence and the inhibitor concentration by red fluorescence. This technique allowed to detect the inhibition/induction levels directly at the single cell level, showing that cells display high or no induction and no intermediate conditions. At the population level, the mean induction /inhibition level would have been artifactually detected as a mean of these two stages, indicating that cells should be studied as such and not always the population level is significant. In other words, in this type of studies the grain is critical.

Relevance for Complex Systems Knowledge
The paper shows the presence of a bistable interface between two monostable conditions (induction vs inhibition). The complexity of the interplay at the molecular level does produce an unstable condition ranging between stable endpoints

Point of Strength
The elegance of the experimental system, especially in 2004, is outstanding. The scientific contribution is that unstable dynamics can occur in the transition between stable conditions. The model used can be replicated at different levels studying biological interacting elements.