ISOLATION OF NEW PLASMIDS FROM HYPERTHERMOPHILIC ARCHAEA OF THE ORDERTHERMOCOCCALES

A collection of 57 strains of hyperthermophilic Archaea from the order Thermococcales was screened for the presence of plasmids; 9 plasmids present in six of these strains were isolated and characterized in ter ms of size and cross-hybridization. The Notl macro-restriction pattern s of genomic DNA of strains harbouring these plasmids were obtained. P yrococcos abyssi strains GE27 and GE23 as well as Thermococcus sp. GE3 1 contained a single plasmid of 3.5 kb (pGN27), 16.8 kb (pGN23) and 5. 3 kb (pGNB1), respectively, whilst the three strains I559, I568 and I6 90 all contained two plasmids of 3.5 kb (pSN559, pSN560, pSN690) and 2 4 kb (pLN559, pLN560, pLN690), respectively. Plasmid pGN27 strongly cr oss-hybridized with the previously described plasmid pGT5 from P. abys si strain GE5, whilst plasmids pGN23 and pGN31 did not cross-hybridize with each other, nor with any other plasmid. The three small plasmids of strains I559, I560 and I690 cross-hybridized, as well as their thr ee large plasmids. Macrorestriction pattern analysis and the results o f plasmid cross-hybridization experiments indicated that these three s trains were different but closely related, and likely belonged to the genus Thermococcus. This study shows that plasmids are widespread in h yperthermophilic archaea, and significantly increases the number and d iversity of plasmids available for laboratory work.