Fig. 1.

Schematic representation of the experimental design. a. Chromosomal modifications in the recipient strain, E. coli MG1655 att-λ::(tetR-Sp^R) att-p21::(CFP/YFP-Kn^R), for the transferred genes. Att-λ and att-p21correspond to the attachment sites of the phage λ and p21, respectively. TetR is the repressor protein controlling the expression of the transferred genes. Sp^R and Kn^R are the resistance genes for spectinomycin and kanamycin, respectively. P_N25 and P_λR are the constitutive promoters. See Methods section for details. b. Depiction of the competition assay. Blue cells with CFP represent the ‘mutant’ strain that carries the pZS*-HGT plasmid containing the introduced gene, whereas yellow cells with YFP represent the ‘wild type’ strain that carries the empty pZS*-HGT plasmid without the introduced gene. The plot illustrates an example where the fitness effect of the gene is deleterious, resulting in a decrease in the frequency of blue cells over time. Numbers inside the segments represents the frequency of the type of the cell with same color