TABLE 1.

Frequency of ideR inactivation events in a merodiploid (ST17) versus a haploid (ST9) strain of ideR

EventNo. of transformantsa
Merodiploid (ST17)Haploid (ST9)
High ironLow ironHigh ironLow iron
Expt 1Expt 2Expt 1Expt 2Expt 1Expt 2Expt 1Expt 2
Wild-type double crossoverb4845404594979494
Mutant double crossoverc525556550003
  • a Strains were plated in 8% sucrose in the absence of antibiotics. One hundred sucrose-resistant colonies from two independent experiments were tested for kanamycin and streptomycin resistance. The second crossover and selection in sucrose were allowed to occur in high-iron (50 μM) or low-iron (10 μM) concentrations. In these experiments, kanamycin-resistant, streptomycin-resistant colonies (spontaneous sucrose-resistant colonies presumably due to sacB mutations) occurred at a frequency of 6% or less. For the differences in the frequencies of mutant double crossover and wild-type double crossover between the merodiploid and the haploid strains, P was <0.0001; χ2 or Fisher's exact test (two tailed) was used.

  • b Kanamycin-sensitive, streptomycin-sensitive colonies.

  • c Kanamycin-resistant, streptomycin-sensitive colonies.