INTEGRATION OF HETEROLOGOUS DNA INTO THE GENOME OF PARACOCCUS-DENITRIFICANS IS MEDIATED BY A FAMILY OF IS1248-RELATED ELEMENTS AND A 2ND TYPE OF INTEGRATIVE RECOMBINATION EVENT

All members of the IS1248 family residing in the genome of Paracoccus denitrificans have been isolated by using a set of insertion sequence entrapment vectors. The family consists of five closely related number s that integrate the entrapment vectors at distinct sites. One of thes e, IS1248b, was sequenced and, except for a single base change, shown to be identical to the previously isolated IS1248a. Southern analysis of genomic DNA with labeled IS1248 revealed different hybridization pa tterns for different isolates of P. denitrificans and Thiosphaera pant otropha. No hybridization was observed with DNA from Thiobacillus vers utus and more distantly related species. From a comparison of the fing erprints it was shown that one of the members of the IS1248 family fou nd in P. denitrificans DSM413 is absent in strain NCIB8944, although t hey are catalogued in international strain catalogues as identical str ains. Furthermore, strains Pd1222 and Pd1235, both derivatives of P. d enitrificans DSM413, were shown to have different patterns of IS1248 h ybridizing restriction fragments. In 14 of 18 strains, the entrapment vectors used in this study were incorporated into the genome via IS124 8-mediated cointegrate formation. In the other four strains, the entra pment vectors were shown to be integrated through a different mechanis m not involving IS1248.