Fig. 2.
From: Competition for nutritional resources masks the true frequency of bacterial mutants
a Growth inhibition of ∼100 Δpst::Km cells plated with increasing amounts of wild-type MG1655 bacteria (wt). Inset shows the growth of phoR cells plated with and without 109 wild-type cells. Each bar represents the mean ± S.E.M. of 5 independent experiments. b Effect of wild-type spent medium on PCM growth. 109 MG1655 cells grown overnight in medium TGP were resuspended in TG2PP and further incubated at 37 ∘C for 48 h. The filtered supernatant of this culture (spent) was mixed with 100 Δpst::Km cells and plated on TG2PP for another 48 h (Δpst + spent). One hundred Δpst::Km (Δpst only) and 100 Δpst::Km mixed with 109 wild-type cells (Δpst + 109 wt) were plated as controls. c Growth inhibition by dead cells. 109 wild-type bacteria were killed either by freeze-thawing in liquid nitrogen (N2 killed cells) or by UV-irradiation (UV killed cells). The dead bacteria were mixed with 100 Δpst cells, plated on TG2PP and incubated for 48 h. Δpst cells alone and Δpst cells mixed with 109 untreated wild-type cells served as controls. Each bar represents the mean ± S.E.M. of 5 independent cultures. d Growth inhibition of Δpst PCMs does not require contact with inhibitor cells. Δpst::Km cells were grown overnight in medium TGP, washed, and diluted in saline. Approximately 100 bacteria were spread on the surface of a 0.22-µm filter which in turn was placed on a TG2PP plate seeded (left) or unseeded (right) with 109ΔphoA::Cm cells. In addition, 100 Δpst::Km bacteria were spread on top of a 3 filter stack placed on the surface of a TG2PP plate. The plates were incubated at 37 ∘C for 48 h