Figure 2.

Lower frequency but higher relative importance of genR transfer via phage delivery (relative to conjugation) occurs at lower bacterial concentration. (a) Transfer frequency was determined after 1 h of conjugation and phage delivery assays in minimal medium with 3.0 g/L glucose and shaken at an Re of 5 × 10⁴. The genR donor (E. coli DH5α harboring plasmid RP4 for conjugation assays or λ phage for phage delivery assays) and recipient (E. coli MG1655) were mixed at a 1:1 ratio. Frequency determined by the plate counting method is presented as bars with the detection limit (10^–6) indicated by the horizontal dashed line; orange dots represent the frequency determined by qPCR analysis. Asterisks (*) indicate significant differences (p < 0.05) between conjugation and phage delivery frequency based on Student’s t-test. “N.D.” refers to “not detected”. (b) Upregulation of conjugation-related genes (traI, traJ, and trbAp) and phage delivery-related genes (lamB and malT) at lower bacterial concentration (twofold gene expression change). The top X-axis depicts decreasing bacterial concentration (CFU/mL). The expression level at a bacterial concentration of 10⁸ CFU/mL was used as the control. Error bars depict ± one standard deviation from the mean of at least three independent replicates.