Chemical Evolution of a Bacterium’s Genome


  • We are grateful to Jean Weissenbach for his constant support and encouragement. We also thank Sophie Tuffet for DNA-composition analysis; Julie Poulain, Karine Labadie, Valérie Barbe, and Béatrice Chane-Woon-Ming for genome sequencing and annotation; Valérie Delmas for strain construction; Isabelle Boko and Angela Lahrz for technical assistance; and Susan Cure, Sven Panke, and Phil Holliger for improving the manuscript.


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Automated selection was used to evolve an Escherichia coli strain unable to synthesize thymine nucleotides into a chemically modified organism whose DNA genome is composed of adenine, cytosine, guanine, and an artificial base, the thymine analogue 5-chlorouracil. Evolving cells were initially observed as irregular filaments and progressively recovered the appearance of short rods typical of wild-type E. coli (see picture).