Abstract
Outer surface protein C (OspC) is the most studied major virulence factor of Borrelia burgdorferi, the causative agent of Lyme disease. The level of OspC varies dramatically among B. burgdorferi strains when cultured in vitro, but little is known about what causes such variation. It has been proposed that the difference in endogenous plasmid contents among strains contribute to variation in OspC phenotype, as B. burgdorferi contains more than 21 endogenous linear (lp) and circular plasmids (cp), and some of which are prone to be lost. In this study, we analyzed several clones isolated from B. burgdorferi strain 297, one of the most commonly used strains for studying ospC expression. By taking advantage of recently published plasmid sequence of strain 297, we developed a multiplex PCR method specifically for rapid plasmid profiling of B. burgdorferi strain 297. We found that some commonly used 297 clones that were thought having a complete plasmid profile, actually lacked some endogenous plasmids. Importantly, the result showed that the difference in plasmid profiles did not contribute to the ospC expression variation among the clones. Furthermore, we found that B. burgdorferi clones expressed different levels of BosR, which in turn led to different levels of RpoS and subsequently, resulted in OspC level variation among B. burgdorferi strains.
Highlights
Lyme disease is the most common arthropod-born disease in the United States, Europe as well as Asia (Samuels, 2011; Radolf et al, 2012)
We found that different clones expressed different levels of BosR, and such difference, not the difference in their plasmid profiles, contributes to the ospC expression variation among B. burgdorferi strains
PL133 and A-1 had very low or undetectable levels of BosR in comparison to high Outer surface protein C (OspC) clones (AH130, B-2, D-1). These results suggest that there is a difference in BosR levels among B. burgdorferi strains, which results in different levels of RpoS, and subsequently, ospC expression variation
Summary
Lyme disease is the most common arthropod-born disease in the United States, Europe as well as Asia (Samuels, 2011; Radolf et al, 2012). Unlike other Gram-negative bacteria that have lipopolysaccharide (LPS) on the outer membrane, B. burgdorferi outer membrane lacks LPS and contains numerous lipoproteins. These outer surface lipoproteins are differentially expressed and play key roles in host adaptation during its enzootic cycle between ticks and mammals (Radolf et al, 2012; Caimano et al, 2016). The major outer surface lipoprotein C (OspC), is induced in B. burgdorferi during nymphal tick feeding and during early phase of mammalian infection, and it plays an essential role for spirochetes to establish early infection and may be important for spirochetal transmission from tick to mammal (Grimm et al, 2004b; Pal et al, 2004; Carrasco et al, 2015a).
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