Over time the bacteria evolved to better suit their environment, adapting to replicate faster on the all-glucose diet. But one colony suddenly took off, consuming the previously indigestible citrate - a molecule that literally would not fit through the original bacteria's membrane. A new breed of E. Coli had evolved to consume the available resources and, over a multi-generational evolutionary battle, came to outperform the original glucose eaters.

Because of the daily samples, there is now a complete genetic paper trail of the changes (although full identification and understanding of the changes will take a little longer). This is an incredible breakthrough in evolutionary research, and a pretty nice argument to break out in the creationism 'debates' ("Prove evolution!" "Okay, I've got it right here IN THIS BOTTLE!")