TABLE 2.
Conjugation frequencies of the S. typhimurium virulence plasmid under various conditions
| Donor | Recipientb | Condition | Conjugation frequency (SE)a |
|---|---|---|---|
| BA1541 | BA770 | LB plate | 4.2 × 10−6 (3.9 × 10−7) |
| BA1541 | BA770 | M9 plate | 2.9 × 10−4 (1.3 × 10−5) |
| BA1541 | BA770 | LB broth | 1.1 × 10−5 (2.5 × 10−6) |
| BA1541 | BA770 | M9 broth | 2.2 × 10−5 (1.6 × 10−6) |
| BA1541 | IR715 | M9 plate | 7.0 × 10−7 (6.8 × 10−8) |
| BA1741 | BA770 | LB plate | 1.4 × 10−6 (2.1 × 10−7) |
| BA1741 | BA770 | M9 plate | 1.7 × 10−4 (2.3 × 10−5) |
| BA1541 | None | LB plate | 9.0 × 10−8 |
| BA1541 | None | M9 plate | 1.1 × 10−7 |
Bacteria were grown as rolling overnight cultures at 37°C in LB medium. A total of 5 μl of donor strain and 50 μl of recipient strain were added to 5 ml of 10 mM MgSO4. This solution was filtered through a 0.45-μm-pore size filter, and the filter was placed on either an M9 minimal plate containing 0.2% glucose (recipe in reference 1) or an LB plate. After overnight incubation at 37°C, the filter was lifted from the plate, added to 5 ml of 10 mM MgSO4, and vortexted to remove the bacteria from the filter. Dilutions were plated on LB plates containing kanamycin (60 μg/ml) to select for donors or on LB plates containing kanamycin and nalidixic acid (50 μg/ml) to select for transconjugants. To perform liquid matings, bacteria were grown as rolling overnight cultures at 37°C in LB medium. A total of 5 μl of donor strain and 50 μl of recipient strain were added to either 1 ml of M9 minimal medium containing 0.2% glucose or 1 ml of LB medium in a 1.5-ml microcentrifuge tube. After a standing overnight incubation at 37°C, dilutions were plated on selective plates as described for filter matings. The conjugation frequency is reported as the number of transconjugants per donor (the number of Kanr Nalr colonies divided by the number of Kanr colonies). The conjugation frequency for each donor-recipient pair was determined by averaging the results of triplicate matings performed on three separate days (nine total matings). The error value is the standard error of the three daily means.
In cases where there is no recipient strain, the value represents the isolation frequency of spontaneously Nalr colonies. These experiments were performed exactly like the others, with triplicate matings on three separate days. However, most filters resulted in no spontaneously Nalr colonies, so an average was not calculated. The value given is the single highest frequency obtained from the nine individual filters.