Bifidobacterial plasmids reported so far are derived from a limited number of strains and plasmids of bifidobacterial type strains isolated from humans are unknown. We found that Bifidobacterium kashiwanohenseJCM 15439 (type strain) isolated from a healthy infant contained two cryptic plasmids, designated pBBKW-1 and pBBKW-2. We determined and analyzed the complete sequences of both plasmids. pBBKW-1 (7716 bp) was predicted to replicate by a rolling-circle mechanism and encode six protein-coding genes, two of which are putative replication proteins. pBBKW-1 seems to be a cointegrate plasmid containing two copies of the plasmid pMG1 from Bifidobacterium longum. pBBKW-2 (2920 bp) was predicted to encode six protein-coding genes and be a theta-type replicating plasmid, which has been reported to be more stable than a rolling circle-type replicating plasmid frequently found in bifidobacteria. Our finding will provide new insights into safe recombinant plasmid constructions for humans.
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