Chemical Evolution of a Bacterium’s Genome

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). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.