(a) At time zero, lysogenic 8325-SR (circles) was spotted on agar plates without antibiotics containing a growing USA300 population (squares) forming autotransduced 8325-SR (triangles). At selected time points, equal size areas of the agar were stamped out, cells extracted and plated on blood agar plates containing the relevant antibiotics. (b,c) Percentage lysogen (8325-SR) in liquid co-cultures with phage susceptible but erythromycin-resistant 8325-4 chrom (b) or USA300 (c) grown in the presence of erythromycin with (open bars) or without citrate (black bars). Percentage autotransductants of total population in the absence on citrate (grey bars) plotted on log-scale axis. No autotransductants were obtained in cultures with citrate. Error bars=s.d., n=3.