Figure 2.

Cassette recruitment in Vibrio cholerae SCI during horizontal gene transfer. (A) Experimental setup of the cassette insertion assay. The pSW23T::attC_aadA7 suicide vector is delivered to N16961 V. cholerae recipient strains containing an integrase expressing vector or the sole endogenous integrase, and the SCI. The delivery occurs by two horizontal gene transfer processes: conjugation from the β2163 donor or natural transformation. As pSW23T cannot replicate in V. cholerae recipient strains, recombinant clones can be selected on appropriate Cm containing plates to evaluate the recombination frequency (see also Results and Materials and Methods). The attC_aadA7 site carried by the suicide vector is represented by a green triangle and the attIA site on the V. cholerae SCI by a red triangle. (B) Frequency of insertion of the pSW23T::attC_aadA7suicide vector into the attIA site. The recombination frequencies were calculated in N16961 V. cholerae wt, ΔintIA and lexA(ind-) strains. Results correspond to recombination frequencies that were normalized after analysis of PCR reactions (Materials and Methods). +IntIA: recipient strains transformed with the pBAD43 integrase expressing vector; -IntIA: control strains transformed with the empty pBAD43 vector. * correspond to the limits of detection. Values represent the mean of at least three independent experiments and error bars correspond to average deviations from the mean.