Characterization of twoBacillus thuringiensisplasmids whose replication is thermosensitive inB. subtilis

Two cryptic plasmids of 8.6 and 15 kb, originating from Bacillus thuringiensis, have been cloned in Escherichia coli. The determination of their physical map shows that the 8.6-kb plasmid harbors the transposon Tn4430 and that the 15-kb plasmid carries Tn4430 plus one copy of the IS231 element. The replication regions were identified on the restriction maps and the segregational stability of derived plasmids containing these regions was analyzed in B. subtillis. The results indicate that the stability of these plasmids is negatively correlated to the temperature. After 30 generations, without selective pressure at 51°C, the two types of plasmids are lost.