Isolation and molecular characterization of a cryptic plasmid from Bifidobacterium longum.

An isolate from the fecal samples of children was identified as Bifidobacterium longum. A plasmid isolated from it pBIFA24 was 4,892 bp with three open reading frames, ORFI, ORFII, and ORFIII. ORFI encoded a replication protein involved in a rolling-circle replication mechanism, and three sets of tandem repeat sequences featuring iteron structure were identified. Secondary structure prediction analysis of ORFII suggested it was a transmembrane protein. ORFIII showed high amino acid sequence identity with some mobilization proteins and contained an oriT sequence.