CONJUGATION IN ARCHAEA - FREQUENT OCCURRENCE OF CONJUGATIVE PLASMIDS IN SULFOLOBUS

We describe five novel conjugative plasmids (CPs) and two subfamilies, each comprising several closely related variants of CPs isolated from colony-cloned strains of the extremely thermophilic, heterotrophic ar chaeon Sulfolobus islandicus, which were obtained by plating of sample s from Icelandic solfataras after liquid enrichment. They are related to each other and to the previously described CP pNOB8 from a Japanese Sulfolobus strain in that they share essential functions and limited similarity of genomes as demonstrated by DNA cross-hybridization and s equences. All these plasmids thus form a family of highly efficient se lf-spreading elements directly transferred from donor into recipient c ells. Conjugation is initiated by pair formation, followed by selectiv e transfer of the plasmids into the recipient and expression of transf er functions. Some of these CPs exclude superconjugation of the transc ipients with closely related CPs. The novel CPs are stable upon conjug ative transfer, but vary upon growth of transcipients. The stability o f the CPs is higher in their original hosts or in related S. islandicu s strains, than in Sulfolobus solfataricus strain PH1 as recipient. Th e deletion variant pING3 has lost the ability to transfer itself but i s still subject to being transferred by the transfer apparatus of its complete relative, pING6. The dissection of genes and functions has be en initiated by characterizing this incomplete variant. (C) 1998 Acade mic Press.