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 th
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