Characterization of the arthropod associated lipoprotein (Alp) in the tick-mammalian transmission cycle of Borrelia turicatae.

Pathogenic species of Borrelia are etiological agents of tick-borne relapsing fever (TBRF). Most species of TBRF Borrelia are transmitted by argasid ticks, and persistent colonization of the salivary glands is vital for spirochete transmission. This is due to the fast-feeding dynamics of the vector. However, the molecular mechanisms leading to vector colonization by the spirochete and their transmission to the vertebrate host remain vague. Previous work in Borrelia hermsii identified the arthropod associated lipoprotein (Alp) as being produced by spirochetes colonizing tick salivary glands. Upon transmission to mice, alp expression was down-regulated and the protein was undetectable in B. hermsii infecting mouse blood. Furthermore, Alp has homologs in multiple TBRF Borrelia species including Borrelia turicatae, Borrelia duttonii, and Borrelia recurrentis. To further evaluate the role of Alp in tick colonization and transmission, the gene was deleted in B. turicatae and the mutant's phenotype was evaluated. Our findings indicate that Alp is dispensable for colonization of the tick salivary glands and for the establishment of infection in laboratory mice.