Transcriptional Profiling the 150 kb Linear Megaplasmid of Borrelia turicatae Suggests a Role in Vector Colonization and Initiating Mammalian Infection

Abstract

Adaptation is key for survival as vector-borne pathogens transmit between the arthropod and vertebrate, and temperature change is an environmental signal inducing alterations in gene expression of tick-borne spirochetes. While plasmids are often associated with adaptation, complex genomes of relapsing fever spirochetes have hindered progress in understanding the mechanisms of vector colonization and transmission. We utilized recent advances in genome sequencing to generate the most complete version of the Borrelia turicatae 150 kb linear megaplasmid (lp150). Additionally, a transcriptional analysis of open reading frames (ORFs) in lp150 was conducted and identified regions that were up-regulated during in vitro cultivation at tick-like growth temperatures (22°C), relative to bacteria grown at 35°C and infected murine blood. Evaluation of the 3’ end of lp150 identified a cluster of ORFs that code for putative surface lipoproteins. With a microbe’s surface proteome serving important roles in pathogenesis, we confirmed the ORFs expression in vitro and in the tick compared to spirochetes infecting murine blood. Transcriptional evaluation of lp150 indicates the plasmid likely has essential roles in vector colonization and/or initiating mammalian infection. These results also provide a much needed transcriptional framework to delineate the molecular mechanisms utilized by relapsing fever spirochetes during their enzootic cycle.

Immunological responses to the relapsing fever spirochete Borrelia turicatae in infected Rhesus macaques: implications for pathogenesis and diagnosis.

“…bta112 was overexpressed in BL21 Star (DE3) cells (Figure 4A), and rabbit immune serum was generated against the recombinant protein. Since native bta112 is up-regulated by B. turicatae during culture at 22°C relative to 35°C (43), spirochetes grown at both temperatures were evaluated to assess temperature-mediated protein production. Optical density analysis of immunoblots probed with the rabbit serum sample generated against rBta112 indicated 3.2-fold increase of the protein in B. turicatae grown at 22°C versus 35°C (Figure 4B, top panel).…”

“…Initially, bta112 was identified as a gene up-regulated by B. turicatae in the tick and at 22°C (tick-like growth conditions) compared to spirochetes isolated from infected murine blood and spirochete grown at 35°C (mammalian-like growth conditions) (43). The protein was evaluated using the Basic Local Alignment Search Tool (BLAST) from NCBI, LipoP1.0, and ScanProsite.…”

The relapsing fever spirochete Borrelia turicatae persists in the highly oxidative environment of its soft‐bodied tick vector

“…Therefore, the populations of B. turicatae present in the salivary glands and midguts of O. turicata ticks must withstand and adapt to distinct microenvironments. This is especially intriguing for the spirochetes colonising the O. turicata salivary glands, which appear to be preadapted for infection of mammalian hosts (Wilder et al, ). Our study suggests that ROS and RNS generated in the O. turicata salivary glands may serve as important environmental signals sensed by B. turicatae to prime it for mammalian infection.…”

Immunological Responses to the Relapsing Fever Spirochete Borrelia turicatae in Infected Rhesus Macaques: Implications for Pathogenesis and Diagnosis

“…Computational analysis of Bta112. Initially, the Bta112 gene was identified as a gene upregulated by B. turicatae in the tick and at 22°C (tick-like growth conditions) compared to spirochetes isolated from infected murine blood and spirochete grown at 35°C (mammalian-like growth conditions) (43). The protein was evaluated using the Basic Local Alignment Search Tool (BLAST) from NCBI, LipoP1.0, and ScanProsite.…”