Characterization and genomic analysis of the Borrelia burgdorferi bacteriophage phiBB-1
Lyme disease is a tick-borne infection caused by the spirochete Borrelia burgdorferi. Spirochetes have highly fragmented genomes composed of a linear chromosome and a constellation of linear and circular plasmids that encode diverse outer surface lipoproteins that facilitate the enzootic cycle. Portions of the B. burgdorferi genome shows evidence of horizontal transfer between strains. The mechanisms of horizontal gene transfer between B. burgdorferi strains remain unclear. Almost all Lyme disease spirochetes are infected by circular cp32 prophages that undergo lytic replication and produce infectious virions called phiBB-1. In the laboratory, phiBB-1 transduces cp32s and shuttle vectors between spirochetes. However, it is not clear the extent that phiBB-1 participates in horizontal gene transfer between Lyme disease spirochetes. Here, we use proteomics and long-read sequencing to characterize phiBB-1 virions and the genetic material they package. Our studies reveal that phiBB-1 packages linear cp32s via a headful mechanism and we identify the cp32 pac region. We also find phiBB-1 packages portions of the entire B. burgdorferi genome, including fragments of the linear chromosome and other plasmids such as lp54, cp26, and others. Additionally, sequencing of packaged DNA allowed us to resolve the covalently closed hairpin telomeres for the linear B. burgdorferi chromosome and all linear plasmids in strain CA-11.2A. Collectively, our study sheds light on the biology of the ubiquitous phiBB-1 phage and further implicates phiBB-1 in the generalized transduction of diverse genes between spirochetes and the maintenance of genetic diversity in Lyme Borrelia.