Decorin-Binding Proteins A and B Confer Distinct Mammalian Cell Type-Specific Attachment by Borrelia burgdorferi, the Lyme Disease Spirochete

Host cell binding is an essential step in colonization by many bacterial pathogens, and the Lyme disease agent, Borrelia burgdorferi, which colonizes multiple tissues, is capable of attachment to diverse cell types. Glycosaminoglycans (GAGs) are ubiquitously expressed on mammalian cells and are recognized by multiple B. burgdorferi surface proteins. We previously showed that B. burgdorferi strains differ in the particular spectrum of GAGs that they recognize, leading to differences in the cultured mammalian cell types that they efficiently bind. The molecular basis of these binding specificities remains undefined, due to the difficulty of analyzing multiple, potentially redundant cell attachment pathways and to the paucity of genetic tools for this pathogen. In the current study, we show that the expression of decorin-binding protein (Dbp) A and/or DbpB, two B. burgdorferi surface proteins that bind GAGs, is sufficient to convert a high-passage nonadherent B. burgdorferi strain into one that efficiently binds 293 epithelial cells. Epithelial cell attachment was mediated by dermatan sulfate, and, consistent with this GAG-binding specificity, these recombinant strains did not bind EA-Hy926 endothelial cells. The GAG-binding properties of bacteria expressing DbpB or DbpA were distinguishable, and DbpB but not DbpA promoted spirochetal attachment to C6 glial cells. Thus, DbpA and DbpB may each play central but distinct roles in cell type-specific binding by Lyme disease spirochetes. This study illustrates that transformation of high-passage B. burgdorferi strains may provide a relatively simple genetic approach to analyze virulence-associated phenotypes conferred by multiple bacterial factors.