Table 1.
Increased evolvability of five knockout strains under single-step antibiotic exposurea
| KEIO strain | Ciprofloxacin MIC (ng/ml) | Gene function | Frequency of resistant populations |
||
|---|---|---|---|---|---|
| Ciprofloxacin (200 ng/ml) | Chloramphenicol (12.5 μg/ml) | Streptomycin (30 μg/ml) | |||
| WT | 18.4 | 0.04 | 0.02 | 0.2 | |
| Δfur mutant | 13.9 | Fe uptake regulation | 0.6 | 0.00 | 0.73 |
| ΔmiaA mutant | 26.7 | Translational fidelity | 0.99 | 0.92 | 1 |
| ΔmutH mutant | 19.4 | Mismatch repair | 1 | 0.92 | 1 |
| ΔmutL mutant | 19.4 | Mismatch repair | 0.95 | 1 | 0.99 |
| ΔmutS mutant | 20.5 | Mismatch repair | 1 | 0.96 | 1 |
a
In the presence of a single antibiotic, five null mutants showed a significant increase in the frequency of resistant populations compared to the WT (BW25113, CGSC 7636). Experiments were conducted with deep-well plates using 96 parallel replicates per strain. In each well, ∼108 cells were exposed to a single antibiotic at a concentration well beyond the MIC. The MICs are 2.2 μg/ml for chloramphenicol and 2.6 μg/ml for streptomycin. After 5 days of incubation, the frequency of resistant populations was determined by transferring ∼2 μl of each culture to an agar plate supplemented with the same concentration of the antibiotic.