Fig. 2

Conjugation-assisted persistence of costly plasmids. For all modeling and experimental results, x-axis is days and y-axis is fraction of cells. a Engineered conjugation. The background strain, B, expresses BFP and Amp^R constitutively⁴⁵. B carries the helper plasmid F_HR (B⁰), which is non-self-transmissible, but can mobilize plasmids in trans. The mobile plasmid K carries the transfer origin (oriT), a kanamycin-resistant gene (Kan^R), and yfp under the control of strong constitutive promoter P_R ⁴⁴. When B carries K, it is denoted B^K. K without transferability (i.e., without oriT) is denoted K⁻, and when carried by B, B^K−. b Long-term dynamics without conjugation. Blue represents plasmid-free and orange plasmid-carrying cells. Shaded lines indicate different initial conditions generated by a strong dilution experimentally (~80 cells/well, 16 wells), or randomly chosen from a uniform distribution (total initial density maintained at 1 × 10⁻⁶, 20 replicates). Bold lines are the average across all initial conditions of corresponding color. Modeling (left): i–iii is α = 1.02, 0.97, and 0.42, respectively, estimated from experimental measurements (Supplementary Fig. 1C). Experiment (right): i–iii is Kan = 0, 0.5, and 2 μg/mL. Quantification is performed using flow cytometry, where the orange lines are cells expressing both BFP and YFP (B^K−), and the blue line are cells expressing BFP only (B⁰). c Long-term dynamics with conjugation. Experiments were done identically to (B), with B^K instead of B^K−. Without antibiotics, the plasmid-carrying population dominated despite the plasmid cost, exhibiting conjugation-assisted persistence. All modeling parameters are identical except for \({\eta _{\rm C}} = 0.025\) h⁻¹. d Nine conjugation plasmids carried by species R (except C with B⁰, which behaves similarly, Supplementary Fig. 3D) exhibit conjugation-assisted persistence. R⁰ was mixed in equal fraction with R^P (P for plasmid generality) and diluted 10,000× daily. CFU from four-to-six double-selection plates were divided by the total number of colonies averaged across four-to-six Cm plates for quantification. Experiments are repeated at least twice. Error bars represent the standard deviation of the four-to-six measurements. The plasmids used are (i) #168, (ii) #193, (iii) R388, (iv) C, (v) #41, (vi) RP4, (vii) K, (viii) PCU1, and (ix) R6K (see Supplementary Tables 1 and 3)