Fig. 2

Selective effect of gentamicin on a Z-mating mixture. Colonies of bacteria from a supernumerary Z-mating step after a cross between Lac⁺ Gm^R MG407-like and Lac⁻ Km^R IL1-like bacteria and a 3-h exposure to kanamycin and gentamicin (KG). They were stabbed into NA and, after incubation, were replica-plated on two McConkey lactose agar plates, one containing 50 μg kanamycin mL⁻¹ alone (LK) and the other 15 μg gentamicin mL⁻¹ in addition (LKG). All colonies grew quite well as Lac⁻ on LK and more or less on LKG where some of the growing bacteria were Lac⁺