Some time ago, you mentioned in a letter that strain 58-278 showed an unusually high rate of mutation to Sr. I recently had
occasion to use this information in experiments adding further proof to the evidence that resistance mutations occur independently
of the selective environment. May I acknowledge the source of this information as a private communication from yourself in
the paper Esther and I are writing?
The experiments use velvet to make replicas of the growth on plain agar to a series of streptomycin agar plates. Starting
with an inoculum from plain broth, heavily spread on plain agar, and incubated a few hours, we find that the Sr mutants on
replica plates are roughly superimposable, showing prior growth of clones. Furthermore, by using the congruent sites on plain
agar for fresh inocula, we enrich for Sr, and in a few such indirect selections obtain Sr mutants in pure culture from populations
never in contact with streptomycin. We finally succeeded in getting one clone from W-1; 58-278 was of course, much easier.
Do you have any further information of the genetics of the high mutability?