FIG. 5.

traR, expressed from pSRKGm, is tightly controlled in Agrobacterium tumefaciens. A culture of A. tumefaciens NTL4 harboring pKPC12 (traR::lacZ) and pSRKGmtraR was grown in ABM minimal medium to early exponential phase, and the culture was split into two equal subcultures, to one of which IPTG (1 mM final concentration) was added. Incubation was continued, each subculture (▪, with IPTG; □, without IPTG) was sampled at the indicated times, and the cells were tested for donor competency in matings with A. tumefaciens C58C1RS as described in Materials and Methods. Growth of the culture, expressed as CFU per ml (○), was monitored by viable-cell counts of samples taken at each time point. Transfer frequencies are expressed as the number of transconjugants obtained per input donor. Error bars show standard deviations.