HOMOLOGY THROUGHOUT THE MULTIPLE 32-KILOBASE CIRCULAR PLASMIDS PRESENT IN LYME-DISEASE SPIROCHETES

We have characterized seven different 32-kb circular plasmids carried by Borrelia burgdorferi isolate B31. Restriction endonuclease recognit ion site mapping and partial sequencing of these plasmids indicated th at all seven are probably closely I elated to each other throughout th eir lengths and have substantial relationships to cp8.3, an 8.3-kb cir cular plasmid of B. burgdorferi sensu late isolate Ip21. With the addi tion of the seven 32-kb plasmids, this bacterial strain is known to ca rry at least 10 linear and 9 circular plasmids. Variant cultures of B. burgdorferi B31 lacking one or more of the 32-kb circular plasmids ar e viable and, at least in some cases, infectious. We have examined a n umber of different natural isolates of Lyme disease borreliae and foun d that all of the B. burgdorferi sensu stricto isolates and most of th e B. burgdorferi sensu late isolates tested appear to carry multiple 3 2-kb circular plasmids related to those of B. burgdorferi B31. The ubi quity of these plasmids suggests that they may be important in the nat ural life cycle of these organisms. They may be highly conjugative pla smids or prophage genomes, which could prole to be useful in genetical ly manipulating B. burgdorferi.