A high-copy-number plasmid capable of replication in thermophilic cyanobacteria

A 2.5 kb high-copy-number plasmid, pMA4 in thermophilic cyanobacterium Syne chococcus sp. MA4 was isolated and characterized to develop a genetic engin eering system for thermophilic cyanobacteria. The copy number of pMA4 was d etermined to be by densitometry about 350/cell. The pMA4 may be a type of r olling-circle plasmid, because a possible rep gene encoding 34 kD-protein a nd a consensus sequence of a double-stranded origin nick site of rolling ci rcle plasmids were found in the pMA4 sequence. The pMA4 was electro-introdu ced into another thermophile, Synechococcus sp. MA19, which is the stronges t poly-beta-hydroxybutyrate (PHB) accumulator in photoautotrophic organisms . The pMA4 was incorporated and retained in MA19. These results indicate th at pMA4 could be developed as a useful vector for thermophilic cyanobacteri a.