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Infection and Immunity, November 2001, p. 7083-7090, Vol. 69, No. 11
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.11.7083-7090.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Analysis of Borrelia burgdorferi vlsE Gene Expression and Recombination in the Tick Vector

Karl J. Indest,1,dagger Jerrilyn K. Howell,2 Mary B. Jacobs,1 Dorothy Scholl-Meeker,1 Steven J. Norris,2 and Mario T. Philipp1,*

Department of Parasitology, Tulane Regional Primate Research Center, Tulane University Health Sciences Center, Covington, Louisiana 70433,1 and Department of Pathology and Laboratory Medicine and Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston, Houston, Texas 770302

Received 20 April 2001/Returned for modification 10 July 2001/Accepted 27 July 2001

Expression and recombination of the antigenic variation vlsE gene of the Lyme disease spirochete Borrelia burgdorferi were analyzed in the tick vector. To assess vlsE expression, Ixodes scapularis nymphs infected with the B. burgdorferi strain B31 were fed on mice for 48 or 96 h or to repletion and then crushed and acetone fixed either immediately thereafter (ticks collected at the two earlier time points) or 4 days after repletion. Unfed nymphs also were examined. At all of the time points investigated, spirochetes were able to bind a rabbit antibody raised against the conserved invariable region 6 of VlsE, as assessed by indirect immunofluorescence, but not preimmune serum from the same rabbit. This same antibody also bound to B31 spirochetes cultivated in vitro. Intensity of fluorescence appeared highest in cultured spirochetes, followed by spirochetes present in unfed ticks. Only a dim fluorescent signal was observed on spirochetes at the 48 and 96 h time points and at day 4 postrepletion. Expression of vlsE in vitro was affected by a rise in pH from 7.0 to 8.0 at 34°C. Hence, vlsE expression appears to be sensitive to environmental cues of the type found in the B. burgdorferi natural history. To assess vlsE recombination, nymphs were capillary fed the B. burgdorferi B31 clonal isolate 5A3. Ticks thus infected were either left to rest for 4 weeks (Group I) or fed to repletion on a mouse (Group II). The contents of each tick from both groups were cultured and 10 B. burgdorferi clones from the spirochetal isolate of each tick were obtained. The vlsE cassettes from several of these clones were amplified by PCR and sequenced. Regardless of whether the isolate was derived from Group I or Group II ticks, no changes were observed in the vlsE sequence. In contrast, vlsE cassettes amplified from B. burgdorferi clones derived from a mouse that was infected with B31-5A3 capillary-fed nymphs showed considerable recombination. It follows that vlsE recombination does not occur in the tick vector.

* Corresponding author. Mailing address: Tulane Regional Primate Research Center, Tulane University Health Sciences Center, 18703 Three Rivers Rd., Covington, LA 70433. Phone: (504) 871-6221. Fax: (504) 871-6390. E-mail: philipp{at}tpc.tulane.edu.

dagger Present address: ASI Services, Vicksburg, MS 39182.

Infection and Immunity, November 2001, p. 7083-7090, Vol. 69, No. 11
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.11.7083-7090.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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