We co-transformed cells with AP1 and one of three CP plasmids (CP2-ACC, CP2-CCC or CP2-GCC) to generate three high-stringency E. coli strains (5, 6 and 7) for infection with SP encoding T7-DdCBE-DddA1 (Fig. 2 and Extended Data Fig. 3a). The gene discussed is CP; the disease is infection.