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Journal of Bacteriology, November 2001, p. 6558-6564, Vol. 183, No. 22
Departments of Microbiology and
Immunology1 and
Pathology,3 New York Medical College,
Valhalla, New York 10595, and Department of Microbiology
and Immunology, West Virginia University, Health Sciences Center,
Morgantown, West Virginia 265062
Received 30 May 2001/Accepted 17 August 2001
With the recent identification of antibiotic resistance phenotypes,
the use of reporter genes, the isolation of null mutants by insertional
inactivation, and the development of extrachromosomal cloning vectors,
genetic analysis of Borrelia burgdorferi is becoming a
reality. A previously described nonmotile, rod-shaped,
kanamycin-resistant B. burgdorferi flaB::Km
null mutant was complemented by electroporation with the erythromycin
resistance plasmid pED3 (a pGK12 derivative) containing the wild-type
flaB sequence and 366 bp upstream from its initiation
codon. The resulting MS17 clone possessed erythromycin and kanamycin
resistance, flat-wave morphology, and microscopic and macroscopic
motility. Several other electroporations with plasmids containing
wild-type flaB and various lengths (198, 366, or 762 bp)
of sequence upstream from the flaB gene starting codon did not lead to functional restoration of the nonmotile
flaB null mutant. DNA hybridization, PCR analysis, and
sequencing indicated that the wild-type flaB gene in
nonmotile clones was present in the introduced extrachromosomal
plasmids, while the motile MS17 clone was a merodiploid containing
single tandem chromosomal copies of mutated
flaB::Km and wild-type flaB
with a 366-bp sequence upstream from its starting codon.
Complementation was thus achieved only when wild-type
flaB was inserted into the borrelial chromosome. Several
possible mechanisms for the failure of complementation for
extrachromosomally located flaB are discussed.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.22.6558-6564.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Complementation of a Nonmotile flaB Mutant of
Borrelia burgdorferi by Chromosomal Integration of a
Plasmid Containing a Wild-Type flaB Allele
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Basic Sciences Bldg., New York Medical
College, Valhalla, NY 10595. Phone: (914) 594-4182. Fax: (914)
594-4176. E-mail: cabello{at}nymc.edu.
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