Figure 6.

Evidence that OmpA contributes to reversion during selection. (A) Appearance of colonies on Congo Red (CR) plates with or without the tetA gene inducer anhydrotetracycline, AnTet (216 nM). The strains are the wild-type ompA strain TR7178 (P⁺ ompA⁺), a strain with ompA deleted (TT27065, ΔompA), and a strain with ompA under tetA promoter control (TT27100, P_Tet ompA⁺). (B) Conjugation efficiency in liquid medium. The donor strain TT27083 (Rif^R/F′lac Cam^R) was mixed with one of the recipient strains TT27036 (P⁺ ompA⁺ Str^R/F⁻), TT27037 (P⁺ ompA⁺ Str^R/F′lac), TT27063 (ΔompA Str^R/F⁻), TT27067 (ΔompA Str^R/F′lac), TT27271 (P_Tet ompA⁺ Str^R/F⁻), or TT27272 (P_Tet ompA⁺ Str^R/F′lac). The inducer AnTet was added during pregrowth and mating in liquid LB medium. Conjugation efficiency is the number of transconjugants Str^R Cam^R per donor cell. (C and D) Total cumulative numbers of revertant Lac⁺ colonies per 10⁸ cells of the tester strain plated. Cells were pregrown to stationary phase in minimal glycerol with or without AnTet (216 nM) and then washed and plated on selective lactose plates with or without AnTc. Strains are TR7178 (P⁺ ompA⁺), TT27100 (P_Tet ompA⁺), and TT27065 (ΔompA). Each data point represents mean ± SEM (error bars) of five independent cultures of each strain.