Identification of a fliG homologue in Treponema denticola

Using a bacteriophage lambda library of Treponema denticola (Td) ATCC 35405 DNA, and, as a reagent, sera derived from individuals with advanced adult periodontal disease, a variety of recombinant clones producing antigens of this oral spirochete have been isolated. Nucleotide sequence analysis of a clone expressing three immunoreactive antigens has revealed the presence of an open reading frame highly homologous to the flagellar switch/motor protein, FliG, which is known to be essential for flagellar assembly and rotation, and chemotaxis in enteric bacteria. The deduced amino-acid sequence of the treponemal FliG protein had 73% similarity (55% identity) to the Bacillus subtilis FliG protein, and showed significant, but lesser homologies to Gram- FliG proteins. Sequence analysis of regions flanking fliG indicated that this gene is immediately preceded by a fliF homologue, further supporting that the cloned DNA encodes FliG of Td. The findings imply that although the signals for control of chemotaxis may be distinctly different in spirochetes, at least some of the molecules involved in torque generation, control of flagellar rotation and signal transduction are highly conserved with other bacteria. The stronger homology of the spirochete FliG with those of Gram+ bacteria is also consistent with recent analyses of other spirochetal genes.