J Bacteriol, May 1998, p. 2418-2425, Vol. 180, No. 9
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Department of Microbiology and Immunology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia 26506-9177,1 and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75235-90502
Received 2 June 1997/Accepted 3 March 1998
The spirochete which causes Lyme disease, Borrelia
burgdorferi, has many features common to other spirochete
species. Outermost is a membrane sheath, and within this sheath are the
cell cylinder and periplasmic flagella (PFs). The PFs are subterminally
attached to the cell cylinder and overlap in the center of the cell.
Most descriptions of the B. burgdorferi flagellar filaments
indicate that these organelles consist of only one flagellin protein
(FlaB). In contrast, the PFs from other spirochete species are
comprised of an outer layer of FlaA and a core of FlaB. We recently
found that a flaA homolog was expressed in B. burgdorferi and that it mapped in a fla/che operon.
These results led us to analyze the PFs and FlaA of B. burgdorferi in detail. Using Triton X-100 to remove the outer
membrane and isolate the PFs, we found that the 38.0-kDa FlaA protein
purified with the PFs in association with the 41.0-kDa FlaB protein. On
the other hand, purifying the PFs by using Sarkosyl resulted in no FlaA
in the isolated PFs. Sarkosyl has been used by others to purify
B. burgdorferi PFs, and our results explain in part their
failure to find FlaA. Unlike other spirochetes, B. burgdorferi FlaA was expressed at a lower level than FlaB. In
characterizing FlaA, we found that it was posttranslationally modified
by glycosylation, and thus it resembles its counterpart from
Serpulina hyodysenteriae. We also tested if FlaA was
synthesized in a spontaneously occurring PF mutant of B. burgdorferi (HB19Fla
). Although this mutant still synthesized
flaA message in amounts similar to the wild-type amounts,
it failed to synthesize FlaA protein. These results suggest that, in
agreement with data found for FlaB and other spirochete flagellar
proteins, FlaA is likely to be regulated on the translational level.
Western blot analysis using Treponema pallidum anti-FlaA
serum indicated that FlaA was antigenically well conserved in several
spirochete species. Taken together, the results indicate that both FlaA
and FlaB comprise the PFs of B. burgdorferi and that they
are regulated differently from flagellin proteins of other bacteria.
Present address: Department of Microbiology, Magainin
Pharmaceuticals, Inc., Plymouth Meeting, PA 19462.
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