FIG 5 .

Selective and titratable removal of individual bacterial strains in mixed cultures. (A) Selective removal of BW25113-T7 and BL21(DE3) in mixed cultures. Equal numbers of BW25113-T7 and BL21(DE3) cells harboring pCas3 and either pCasA-E (+ casABCDE) or pCasA-E′ (− casABCDE) were mixed prior to preparation for electroporation. Mixed cultures electroporated with the indicated pCRISPR plasmid were plated on LB agar containing IPTG, X-Gal, l-arabinose, IPTG, and antibiotics. Only BL21(DE3) possesses the lacZ gene, which yields blue colonies (see Fig. S8 in the supplemental material). Plates are representative of three independent experiments. (B) Titratable removal of BL21(DE3) in mixed cultures. Transformations were conducted similarly to the method described for panel A except that cells were transformed with different ratios of the E. coli B-targeting plasmid (pCRISPR-ogr) and the nontargeting plasmid (pCRISPR) for a total of 100 ng. The ratio of blue to white colonies was normalized to the ratio of blue to white colonies for the same culture transformed with the pCRISPR plasmid. Values represent the geometric means and SEM of data from three independent experiments.