Development of genetic system to inactivate a Borrelia turicatae surface protein selectively produced within the salivary glands of the arthropod vector.

Abstract

Borrelia turicatae, an agent of tick-borne relapsing fever, is an example of a pathogen that can adapt to disparate conditions found when colonizing the mammalian host and arthropod vector. However, little is known about the genetic factors necessary during the tick-mammalian infectious cycle, therefore we developed a genetic system to transform this species of spirochete. We also identified a plasmid gene that was up-regulated in vitro when B. turicatae was grown in conditions mimicking the tick environment. This 40 kilodalton protein was predicted to be surface localized and designated the Borrelia repeat protein A (brpA) due to the redundancy of the amino acid motif Gln-Gly-Asn-Val-Glu.Quantitative reverse-transcriptase polymerase chain reaction using RNA from B. turicatae infected ticks and mice indicated differential regulation of brpA during the tick-mammalian infectious cycle. The surface localization was determined, and production of the protein within the salivary glands of the tick was demonstrated. We then applied a novel genetic system for B. turicatae to inactivate brpA and examined the role of the gene product for vector colonization and the ability to establish murine infection.These results demonstrate the complexity of protein production in a population of spirochetes within the tick. Additionally, the development of a genetic system is important for future studies to evaluate the requirement of specific B. turicatae genes for vector colonization and transmission.