Characterisation of a cryptic plasmid from an Antarctic bacterium Pedobacter cryoconitis strain BG5

A cryptic plasmid, pMWHK1 recovered from an Antarctic bacterium Pedobacter cryoconitis BG5 was sequenced and characterised. The plasmid is a circular 6206 bp molecule with eight putative open reading frames designated as orf1, orf2, orf3, orf4, orf5, orf6, orf7 and orf8. All the putative open reading frames of pMWHK1 are found to be actively transcribed. Proteins encoded by orf2 and orf4 are predicted to be responsible for the mobilization and replication of the plasmid respectively. orf4 shares 55% and 61% identities with the theta-type Rep proteins from two strains of Riemerella anatipestifer. This suggests that pMWHK1 could be a member of the theta-type replicating plasmid. The origin of replication is located within the AT-rich region upstream of orf4. orf5 and orf6 encode bacterial toxin-antitoxin proteins predicted to maintain plasmid stability. orf3 encodes an entry exclusion protein that is hypothetically involved in reducing the frequency of DNA transfer through conjugation. orf1, orf7 and orf8 encode proteins with unknown functions. Plasmid, pMWHK1 is stably maintained in P. cryoconitis BG5 at 20 °C.

► A cryptic plasmid of Pedobacter cryoconitis BG5, pMWHK1 was sequenced.
► Plasmid, pMWHK1 has 8 open reading frames.
► The putative toxin and antitoxin system of the plasmid is to ensure its stability.
► pMWHK1 inherited a mobilization gene (orf2) from a Gram-positive bacterium.
► Gene encoding the relaxase is present in pMWHK1 but the cis-acting oriT is absent.