Defining the Plasmid-Borne Restriction-Modification Systems of the Lyme Disease Spirochete Borrelia burgdorferi

The restriction-modification (R-M) systems of many bacteria present a barrier to the stable introduction of foreign DNA. The Lyme disease spirocheteBorrelia burgdorferi has two plasmid-borne putative R-M genes,bbe02 andbbq67 , whose presence limits transformation by shuttle vector DNA fromEscherichia coli . We show that both thebbe02 andbbq67 loci in recipientB. burgdorferi limit transformation with shuttle vector DNA fromE. coli , irrespective of itsdam ,dcm , orhsd methylation status. However, plasmid DNA purified fromB. burgdorferi transformed naïveB. burgdorferi much more efficiently than plasmid DNA fromE. coli , particularly when thebbe02 andbbq67 genotypes of theB. burgdorferi DNA source matched those of the recipient. We detected adenine methylation of plasmid DNA prepared fromB. burgdorferi that carriedbbe02 andbbq67 . These results indicate that thebbe02 andbbq67 loci ofB. burgdorferi encode distinct R-M enzymes that methylate endogenous DNA and cleave foreign DNA lacking the same sequence-specific modification. Our findings have basic implications for horizontal gene transfer amongB. burgdorferi strains with distinct plasmid contents. Further characterization and identification of the nucleotide sequences recognized by BBE02 and BBQ67 will facilitate efficient genetic manipulation of this pathogenic spirochete.