Characterization of a novel cryptic plasmid, pHLHK26, in Laribacter hongkongensis

We report the complete nucleotide sequence and characterization of a cryptic plasmid, pHLHK26, recovered from a strain of Laribacter hongkongensis isolated from a patient with community acquired gastroenteritis. pHLHK26 consists of 8700 bp, with G + C content 51.3%. The copy number (mean±SD) is 0.57±0.07 and it is stable after four passages (about 240 generations) in the absence of selection. There is a predicted origin of replication that consists of a DnaA box and five 22-bp direct repeats. pHLHK26 has four ORFs with two genes encoded in the sense direction and the other two in antisense direction. These four ORFs encode a putative plasmid partitioning protein of the ParA family, a putative protein that contains putative ADP-ribose 1"-phosphatase activity belonging to the Appr-1 -p processing enzyme family, a putative recombinase (TniR) of the resolvase/invertase family, and a putative replication protein, respectively. We speculate that pHLHK26 is a theta, possibly Class A, replicative plasmid, as it contains an origin of replication with AT-rich region, a number of herons and a DnaA box and a gene that encodes a replicative protein most homologous to those of other theta replicative plasmids and it shares eight of the nine positions of the consensus sequence TTAT(C/A)CA(C/A)A (TTTTCCACA in pHLHK26) in the DnaA boxes observed in other classical examples of Class A plasmids of this group.