AN UNEXPECTED FLAA HOMOLOG IS PRESENT AND EXPRESSED IN BORRELIA-BURGDORFERI

Most investigators have assumed that the periplasmic flagella (PFs) of Borrelia burgdorferi are composed of only one flagellin protein. The PFs of most other spirochete species are complex: these PFs contain an outer sheath of FlaA proteins and a core filament of FlaB proteins. D uring an analysis of a chemotaxis gene cluster of B. burgdorferi 212, we were surprised to find a flaA gene homolog with a deduced polypepti de having 54 to 58% similarity to FlaA from other spirochetes. Like ot her FlaA proteins, B. burgdorferi FlaA has a conserved signal sequence at its N terminus. Based on reverse transcription-PCR and primer exte nsion analysis, this flaA homolog and five chemotaxis genes constitute a motility-chemotaxis operon. Immunoblots using anti-FlaA serum from Treponema pallidum and a lysate of B. burgdorferi showed strong reacti vity to a protein of 38.0 kDa, which is consistent with the expression of flaA in growing cells.