Among forty strains of marine cyanobacteria isolated in our laboratory, five strains had 1-3 different plasmids. The unicellular marine cyanobacterium, Synechococcus sp. NKBG 042902, contains at least three plasmids (pSY09, pSY10, and pSY11). However, these plasmids are cryptic. Therefore, a hybrid plasmid pUSY02 containing the 1.4kb HindIII fragment of pSY11 and Escherichia coli plasmid pUC18 was constructed. The plasmid pUSY02 transformed both marine Synechococcus sp. NKBG042902-YG1116, which is a cured strain, and fresh water Anacystis nidulans R2 by dark incubation or Ca2+ treatment. However, the plasmid pSG111 constructed from the plasmid DNA of A. nidulans R2 failed to transform marine Synechococcus sp. Electroporation was also applicable to transformation of marine Synechococcus sp. and fresh water A. nidulans R2. The plasmid pUSY02 was rapidly introduced into marine Synechococcus sp.
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