Selection-Driven Accumulation of Suppressor Mutants in Bacillus subtilis: The Apparent High Mutation Frequency of the Cryptic gudB Gene and the Rapid Clonal Expansion of gudB+ Suppressors Are Due to Growth under Selection
Figure 2
Intraspecies competition experiment to identify the selective advantage for keeping the gudBCR allele in the laboratory strain 168.
(A) Mixed populations of strains BP40 (rocG+ gudBCR amyE::yfp) and BP52 (rocG+ gudB+ amyE::cfp) or BP41 (rocG+ gudBCR amyE::cfp) and BP156 (rocG+ gudB+ amyE::yfp) were grown for up to 24 h in C minimal medium supplemented with glucose and ammonium, and in minimal medium supplemented with glucose, ammonium and glutamate. (B) Prior to co-cultivation (0 h), and after 7 h and 24 h of growth dilutions of cells were plated on complex medium. The surviving cells that emerged after 12 h of incubation were identified by fluorescence microscopy and counted. Exposure time, 0.6 s; Scale bar, 1 mm. (C) Outcome of the competition experiment. The bars represent standard deviations for at least four independently repeated experiments.