Borrelia burgdorferi small lipoprotein Lp6.6 is a member of multiple protein complexes in the outer membrane and facilitates pathogen transmission from ticks to mice

Abstract

Borrelia burgdorferi lipoprotein Lp6.6 is a differentially produced spirochete antigen. An assessment of lp6.6 expression covering representative stages of the infectious cycle of spirochetes demonstrates that the gene is solely expressed during pathogen persistence in ticks. Deletion of lp6.6 in infectious B. burgdorferi did not influence in vitro growth, or its ability to persist and induce inflammation in mice, migrate to larval or nymphal ticks or survive through the larval-nymphal molt. However, Lp6.6-deficient spirochetes displayed significant impairment in their ability to transmit from infected ticks to naïve mice, which was restored upon genetic complementation of the mutant with a wild-type copy of lp6.6, establishing that Lp6.6 plays a role in pathogen transmission from ticks to mammals. Lp6.6 is a subsurface, yet highly abundant, outer membrane antigen. Two-dimensional blue native/SDS-PAGE coupled with liquid chromatography-mass spectrometry (LC-MS/MS) analysis and protein cross-linking studies independently shows that Lp6.6 exists in multiple protein complexes in the outer membrane. We speculate that the function of Lp6.6 is connected to the physiological processes of these membrane complexes. Further characterization of differentially produced membrane antigens and associated protein complexes will likely aid in our understanding of the molecular details of B. burgdorferi persistence and transmission through a complex enzootic cycle.

Lipoproteins of Bacterial Pathogens

“…The differential expression of lipoproteins by B. burgdorferi is a characteristic of its transition to life inside the mammalian host (27). The 6.6-kDa lipoprotein of B. burgdorferi is one such protein that has been shown to be involved in the formation of outer membrane protein complexes and is consistently expressed within ticks (139). This pattern of expression is analogous that of to other Borrelia lipoproteins important in the vector, such as OspA and OspB (202).…”

Borrelia burgdorferi bba66 Gene Inactivation Results in Attenuated Mouse Infection by Tick Transmission

“…Recent research investigating borrelia-vector interactions have focused on inactivation of global regulators, individual genes, and replicons to advance our understanding of B. burgdorferi tick colonization and persistence and vector transmission mechanisms (1,4,7,18,(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54). The loss of BBA66 activity did not completely abolish the ability of B. burgdorferi to invade the host by tick bite (at least when more than 4 ticks/mouse fed to repletion), but mouse infectivity was significantly impaired.…”

A Surface Enolase Participates in Borrelia burgdorferi-Plasminogen Interaction and Contributes to Pathogen Survival within Feeding Ticks

“…For quantitative analysis of gene expression, the target transcripts were normalized to the number of flaB transcripts. Since there is probably no suitable gene, or method, to accurately quantify spirochete levels in vivo, we used flaB RNA-based qRT-PCR to measure spirochete burdens which also produces similar patterns in the differences of the tissue burdens of B. burgdorferi when using DNAbased qPCR (47). For quantitative measurement of B. burgdorferi burden in infected tissues, flaB transcripts were normalized to mouse or tick ␤-actin levels.…”