Figure 9. Global regulators arcA and rpoS provide a comprehensive metabolic shift during adaptation that circumvents epistatic bottlenecks.

Adaptation to the amino acid rich conditions of BHI by E.coli are consistent with a ‘metabolic selection’ that provides a facile strategy for shifting environments. Up-regulated systems (green) are associated with the movement of abundant amino acids into the cell coupled with an increased capacity for catabolic metabolism through the TCA cycle with excess nitrogen being secreted as putrescine. Down-regulated systems (red) include components of the starvation stress response consistent with the maintenance of a new nutrient rich homeostasis.