Comparative genomics of Borrelia lusitaniae

Human Lyme disease is a frequent tick-borne human disease that is caused by several species in the Borrelia burgdorferi sensu lato (BBSL) clade of the bacterial spirochete genus Borrelia. Although Borrelia lusitaniae does not appear to be a major cause of this disease, it has been isolated from human patients. This Borrelia species is unusual in that its vertebrate reservoir includes reptiles in Europe and North Africa. We describe here the complete genome sequences of three B. lusitaniae isolates, PotiB2T (the species type strain) and PotiB3 that represent a Southern Portugal-North African lineage and PoHL1 that represents a Northern Portugal-Central Europe lineage. Like other members of this genus, their genomes include linear chromosomes as well as numerous circular and linear plasmids. Their total genomes contain 1,202,579 bp (PotiB2T), 1,171,499 bp (PotiB3), 1,155,617 bp (PoHL1), and they carry eight (PotiB2T and PotiB3) or six (PoHL1) plasmids. We discuss the differences and similarities of these genomes with other members of the BBSL species group. A most unusual feature of the B. lusitaniae genomes is that their important cp26 plasmids are partially degraded dimers of the cp26 plasmid that is present in all other BBSL isolates analyzed to date. The cp26 plasmid has been shown to be essential for growth of B. burgdorferi sensu stricto B31T. The B. lusitaniae dimer cp26 plasmids carry multiple ospC genes of different types, which is unique to this species. OspC is an important protein that is required for the establishment of mammalian infection by B. burgdorferi B31T and tick salivary gland infection in Borrelia afzelii. It remains unclear how genes of more than one OspC type in one strain might affect the infection process.