TABLE 2.
Strain SS1 susceptibility to spontaneous and Mtz-induced mutation
| Strain | Growth conditiona (μg of MTZ/ml) | Mean no. of Rifr colonies/108 cellsb |
|---|---|---|
| Wild-type SS1 | 0 | 2 ± 1 |
| 0.5 | 144 ± 35 | |
| Mtzr SS1c | 0 | 2 ± 1 |
| 32 | 44 ± 14 | |
| 64 | 322 ± 181 |
a
Bacteria were grown on media without MTZ or with the indicated concentrations of MTZ for 48 h before being spread on medium with rifampin, essentially as described in reference 26.
b
Data are the mean values and standard deviations of five independent populations.
c
This strain contains the rdxAΔ111 allele that was used in DNA transformation and also contains a frameshift mutation in frxA (loss of one AT pair in a run of seven AT pairs at position 48). This additional point mutation was selected (and may have been induced as well) when transformed cells were spread on medium with 3 μg of MTZ/ml (see reference 26).