Analysis of Borrelia burgdorferi membrane architecture by freeze-fracture electron microscopy

Abstract

Freeze-fracture electron microscopy was used to investigate the membrane architectures of high-passage Borrelia burgdorferi B31 and low- and high-passage isolates of B. burgdorferi N40. In all three organisms, fractures occurred almost exclusively through the outer membrane (OM), and the large majority of intramembranous particles were distributed randomly throughout the concave OM leaflet. The density of intramembranous particles in the concave OM leaflet of the high-passage N40 isolate was significantly greater than that in the corresponding leaflet of the low-passage N40 isolate. Also noted in the OMs of all three organisms were unusual structures, designated linear bodies, which typically were more or less perpendicular to the axis of the bacterium. A comparison of freeze-fractured B. burgdorferi and Treponema pallidum, the syphilis spirochete, revealed that the OM architectures of these two pathogens differed markedly. All large membrane blebs appeared to be bounded by a membrane identical to the OM of B. burgdorferi whole cells; in some blebs, the fracture plane also revealed a second bilayer closely resembling the B. burgdorferi cytoplasmic membrane. Aggregation of the lipoprotein immunogens outer surface protein A (OspA) and OspB on the bacterial surface by incubation of B. burgdorferi B31 with specific polyclonal antisera did not affect the distribution of OM particles, supporting the contention that lipoproteins do not form particles in freeze-fractured OMs. The expression of poorly immunogenic, surface-exposed proteins as virulence determinants may be part of the parasitic strategy used by B. burgdorferi to establish and maintain chronic infection in Lyme disease.

Virulent strain associated outer membrane proteins of Borrelia burgdorferi.

“…5 and summarized in Table III. The diameters of the organisms shown (between 230-250 nm) are consistent with those of whole intact cells ( 1,12,19,24) and endoflagella were not observed, indicating that the B. burgdorferi used were structurally intact. The gold particles observed thus correspond to antibody-bound surface antigens.…”

“…Such membrane-spanning proteins have distinct surface exposed domains and are seen as particles by freeze-fracture analysis (18,19,22,24) ( 18,19,22). While these freeze-fracture analyses do not address the possibility that a certain proportion of the Osp lipoproteins are surface exposed, it does highlight the fact that unidentified and uncharacterized outer membrane-spanning proteins are present on the surface of B. burgdorferi.…”

Isolation and partial characterization of Borrelia burgdorferi inner and outer membranes by using isopycnic centrifugation

“…Dry weights were determined as described by Kotarski and Salyers (19 (Fig. 1A) was within the range of measured densities of outer membranes of gram-negative bacteria (19,32). The density of peak II was 1.16 g/cm3.…”

Hypercholesterolemia and ApoE deficiency result in severe infection with Lyme disease and relapsing-fever Borrelia

“…The borreliae also have cholesterol glycolipids: cholesteryl 6-O-acyl-β-D-galactopyranoside and cholesteryl-β-D-galacto-pyranoside in B. burgdorferi; and 6-O-acylated cholesteryl β-D-glucopyranoside and cholesteryl β-D-glucopyranoside in relapsing-fever Borrelia. They also have noncholesterol glycolipids, monogalactosyl-diacylglycerol in B. burgdorferi and monoglucosyl-diacylglycerol in relapsing-fever Borrelia, as well as many lipoproteins (7)(8)(9)(10)(11)(12)(13)(14)(15). The presence of cholesterol is not common among prokaryotes, but it is increasingly being reported in bacterial pathogens other than Borrelia spp., including species of Helicobacter, Mycoplasma, Ehrlichia, Anaplasma, and Brachyspira (16)(17)(18)(19)(20).…”