Cryptic plasmid pKA22 isolated from the naphthalene degrading derivative of Rhodococcus rhodochrous NCIMB13064.

Cryptic plasmids were found in Rhodococcus rhodochrous NCIMB13064 derivatives which had lost the ability to utilize short-chain 1-chloroalkanes (chain length C3-C10) and had acquired the ability to degrade naphthalene. The reversions of these derivatives to the original phenotype were accompanied by the loss of the cryptic plasmids. The 4969-bp pKA22 plasmid was cloned in Escherichia coli and sequenced. This plasmid encodes a putative 33,200-Da protein which contains motifs typical of theta replicase proteins and shows a high degree of similarity to a putative theta replicase from Brevibacterium linens plasmid pRBL1 and to a putative protein encoded by ORF1 of the plasmid pAL5000 from Mycobacterium fortuitum. Two sets of long direct repeats were found in pKA22 which may be involved in the replication of the plasmid and recombination processes.