2.4 Conjugation assay
Prior to the conjugation assay, the E. coli strains were incubated overnight at 30°C on solid lysogeny broth (Lennox) (LB) agar (VWR) supplemented with antibiotics, 30 ug kanamycin/ml for donor/R27 and 10 ug tetracycline/ml for donor/pB10. A single colony per replicate used, was grown in 5 ml LB for 3 hours and enumerated by flow cytometry. Donors and recipients were resuspended in 0.9 % (9 g/l) NaCl solution and mixed in a 1:1 ratio. The 0.2 μm mixed cellulose ester (MCE) filter (Advantec®) was placed on solidified LB agar plates and the mixture was pipetted on to 54 mm2 corresponding to an initial cell density of 3.6 x 105 cells/mm2. The plates were then incubated for 20 hours at 30°C, at which state cells were harvested; the filter was transferred to a 0.9 % NaCl solution where cells were washed off and the suspension was stored at 4°C.