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Infection and Immunity, November 1999, p. 6008-6018, Vol. 67, No. 11
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Identification, Characterization, and Expression of Three New Members of the Borrelia burgdorferi Mlp (2.9) Lipoprotein Gene Family

Xiaofeng Yang,1 Taissia G. Popova,1 Kayla E. Hagman,1 Stephen K. Wikel,2 George B. Schoeler,2 Melissa J. Caimano,3 Justin D. Radolf,3 and Michael V. Norgard1,*

Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 752351; Oklahoma State University, Stillwater, Oklahoma 740782; and Center for Microbial Pathogenesis, University of Connecticut Health Center, Farmington, Connecticut 060303

Received 8 July 1999/Returned for modification 13 August 1999/Accepted 23 August 1999

We previously reported on the existence of a family of lipoprotein genes, designated 2.9 lipoprotein genes, encoded in at least seven versions on the circular (supercoiled) cp32 and cp18 plasmids of Borrelia burgdorferi 297. A distinguishing feature of the 2.9 lipoproteins were highly similar signal sequences but variable mature polypeptides that segregated into two antigenic classes. Further screenings of B. burgdorferi 297 genomic libraries led to the identification of three additional 2.9 lipoprotein genes, renamed herein mlp, for multicopy lipoprotein genes. Computer analyses and immunoblotting revealed that Mlp-9 segregated with the antigenic class I lipoproteins, whereas Mlp-8 and Mlp-10 were members of class II. Northern blotting showed that all three of the mlp genes were expressed when B. burgdorferi was cultivated in vitro at 34°C, although mlp-9 and mlp-10 transcripts were expressed at very low levels. Additional combined immunoblotting and comparative reverse transcription-PCR analyses performed on borreliae cultivated in vitro at 23, 34, or 37°C indicated that although Mlp-8 was substantially more abundant than Mlp-9 or Mlp-10, all three of the mlp genes were upregulated during B. burgdorferi replication at 37°C. Expression of the same three lipoproteins was further enhanced upon growth of the spirochetes within dialysis membrane chambers (DMCs) implanted intraperitoneally in rats (i.e., spirochetes in a mammalian host-adapted state), suggesting that temperature alone did not account for maximal upregulation of the mlp genes. That certain mlp genes are likely expressed during the growth of B. burgdorferi in mammalian tissues was supported by findings of antibodies against all three Mlp lipoproteins in mice after challenge with Ixodes scapularis nymphs harboring B. burgdorferi 297. The combined data suggest that as opposed to being differentially expressed in any reciprocal fashion (e.g., OspA/OspC), at least three mlp genes are simultaneously upregulated by temperature (37°C) and some other mammalian host factor(s). The findings have importance not only for understanding alternative modes of differential antigen expression by B. burgdorferi but also for assessing whether one or more of the Mlp lipoproteins represent new candidate vaccinogens for Lyme disease.

* Corresponding author. Mailing address: Department of Microbiology, U.T. Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75235-9048. Phone: (214) 648-5900. Fax: (214) 648-5905. E-mail: norgard{at}utsw.swmed.edu.

Infection and Immunity, November 1999, p. 6008-6018, Vol. 67, No. 11
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.