Elimination of Canonical Amino Acid from Escherichia coli by Experimental Evolution

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In all the theories of the evolution of the genetic code, the number of amino acids is hypothesized to have gradually increased from a few to the twenty that now constitute the building-blocks of proteins in living cells. The objective of this research is to recreate a possible evolutionary intermediate in which a living organism contains 19 and not 20 amino acids. This objective would give insight into how protein structures adapt to mutation and open possibilities in terms of designing and selecting organisms adapted to a different chemical composition. Based on encouraging results from recent experiments, this objective will be accomplished by placing a population under selective pressure for the loss of a given amino acid. Two different strategies have been designed to replace isoleucine by valine and threonine by serine in Escherichia coli. These strategies combine selection strategies that exploit classical strain constructions with the use of a continuous culture apparatus that allows long-term experiments.