Evolving a mitigation of the stress response pathway to change the basic chemistry of life

We conducted an adaptive laboratory evolution to push the limits of the code restriction, by evolving Escherichia coli to replace tryptophan fully, thought to be the latest addition to the genetic code, with an analog. We identified an overshooting of the stress response system as the main inhibiting factor for limiting ancestral growth upon exposure to the analog, a metabolic precursor of [3,2]Tpa, and Trp limitation.