Characterization of Peptidoglycan, and the Enzymes that Synthesize it, in Borrelia burgdorferi and Insights into the Peptidoglycan of Other Pathogenic Borrelia

Peptidoglycan (PG) is an essential cell-wall biopolymer in virtually all bacteria. It is composed of glycan strands of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) crosslinked by peptide chains of alternating D- and L- amino acids and diamines. PG plays an important role in 1) cell elongation and division, 2) cell strength and morphology, 3) antibiotic susceptibility, and 4) host immune detection and modulation. While differences in peptide chains are common, deviations in glycan strand composition were not previously known to occur. Here, we provide characterization of the first known deviation to bacterial glycan strand composition — GlcNAc-GlcNAc-anhMurNAc (G-G- anhM) in Borrelia burgdorferi, the causative agent of Lyme disease. B. burgdorferi with less G-G-anhM were found to be significantly less motile, flexible, and stress-tolerant while possessing gross morphological defects and less overall PG. Our studies also characterized the muropeptide profile of Borrelia afzelii, Borrelia garinii, and Borrelia hermsii — species of Borrelia associated with causing different disease manifestations of Lyme disease, and relapsing fever, respectively. These species were found to incorporate appreciable amounts of G-G-anhM into their PG, suggesting an evolutionary adaptation to life inside a tick that predates the differentiation of Lyme disease and relapsing fever Borrelia. Finally, we provide partial characterization of a putative penicillin-binding protein in B. burgdorferi — a class of highly conserved PG synthesis enzymes present in the vast majority of bacteria. Collectively, the work in this thesis furthers our understanding of the structure, function, and synthesis of PG in Borrelia.