Stable and unstable alterations of the host-induced modification properties of Escherichia coli B, K and C

Strains with altered properties of host-induced modification (HIM) have been isolated. Someof these variants were stable on first isolation but the majority of them are unstable. They segregate during many generations two different stable HIM phenotypes and a third type which continues to segregate. Usually this instability disappears during repeated serial single colonyisolation, but in one case it still persisted after nine such single colony isolation steps. Evidence suggesting that they are unstable partial diploids is discussed.