A highly conserved plasmid from the extreme thermophile Thermotoga maritima MC24 is a member of a family of plasmids distributed worldwide

We have screened Thermotoga strains; isolated from hydrothermal vents near the Kuril Islands, for the presence of plasmid DNA. The miniplasmid pMC24 w as isolated from the extreme thermophilic eubacteria Thermotoga maritima an d sequenced, showing it to be a plasmid of 846 bp. It was found, from a sea rch of the databases, to be closely related to the previously described The rmotoga miniplasmid pRQ7, isolated from a strain found on the Azore Islands , and was distinguished by only two point mutations. These changes resulted in two consecutive frameshifts altering a region encoding 9 amino acids in the Rep-coding region. We have also shown that pMC24, as with pRQ7, is neg atively supercoiled. It seems that negatively supercoiled miniplasmids rela ted to pRQ7 are spread worldwide and strongly maintained among Thermotoga s trains. (C) 1999 Academic Press.