Incompatibility among α-hemolytic plasmids studied after inactivation of the α-hemolysin gene by transposition of Tn802

Five α-hemolytic plasmids were studied with respect to their molecular and genetic properties. Their molecular weights ranged from 48 to 93 Mdal. Digestion with HindIII restriction endonuclease indicated that they were all clearly different plasmids although similarities in their band patterns were observed. Plasmids pSU1, pSU105, and pSU316 produce F-like pili. Incompatibility studies between Hly plasmids were prevented by lack of markers other than α-hemolysin production. In order to overcome this problem, the inactivating properties of the transposable element Tn802 were used. Several Hly plasmids that have lost the ability to produce α-hemolysin were isolated after insertion of the ampicillin transposon Tn802. Incompatibility between the parental plasmids and their Tn802 derivatives suggests that α-hemolytic plasmids have spread over, at least, four incompatibility groups. Plasmids pSU1 and pSU105 were found to be incompatible with Hly-P212, the only representative, so far, of IncFVI. Plasmid pSU316 was incompatible both with ColB-K98 and R124, which suggests the existance of a FIII-FIV incompatibility complex. In addition, pSU5 and pSU233 were compatible with each other and with pSU316, pSU1, pSU105, and Hly-P212. They also produce a different type of pili from this test plasmids.