(A–C) Transformation is enhanced in T6SS-positive predator cells. To induce natural competence, cultures were grown on chitin flakes. Bacteria were grown as co-cultures (predator + prey) or as monocultures (predator only). In the latter case, purified gDNA served as the transforming material. Transformants were selected based on their acquisition of the aph resistance cassette located in vipA, VCA0747, or lacZ on chr1 or chr2, as indicated below the graphs. The killing capability of each strain is indicated below the graph (e.g., T6SS + or -). Transformation frequencies are shown on the Y-axis (± SD, as indicated by the error bars) and depict averages of at least two biologically independent experiments (corresponding to the experiments described in Figure 4 and maintaining the same color code). N.A., not applicable. (D) The location of the resistance genes does not influence the transformation efficiency. Natural transformability of the WT (plain bars) or its T6SS-minus derivative (T6SS-; ΔvipA; hashed bars) was scored using gDNA as the transforming material. The gDNA samples were derived from the prey strains of conditions j and l–p and the respective genotype is shown below the graph. Transformation frequencies were scored based on the acquisition of the aph resistance cassette, which was integrated into different genes on chromosome 1 or 2 (chr 1/chr 2). Data represent the average of three independent experiments (± SD). (A–D) Statistical significance is indicated (*p<0.05; **p<0.01; ns, not significant).