A culture of Y-87 (B-M-Lac1-V1r) has just been sent off to you. Fortunately, we were able to recover and repurify it. It
should behave all right now. If now, a few single-colony streakings on lactose EMB agar will certainly do the trick.
This culture has the interesting faculty of being "mutabile" -- the classical instances of bacterial mutation, namely
lactose-positive papillae forming on Lac-EMB agar. Other recurrences of Lac1- have been found which differ in their mutability,
and my wife is studying the genetic basis of these differences in mutation rate. So far, they seem to represent asseries
of alleles, one might almost say iso-alleles. However, some of the stocks throw off pepiline which are not reverse-mutations,
but "suppressor" mutations, i.e. yield Lac-/ which when crossed with the wild type Lac-/ give Lac- recombinants.
I thought you might be interested to observe this phenomenon on Lac EMB.