GENETIC AND TRANSCRIPTIONAL ANALYSIS OF FLGB FLAGELLAR OPERON CONSTITUENTS IN THE ORAL SPIROCHETE TREPONEMA-DENTICOLA AND THEIR HETEROLOGOUS EXPRESSION IN ENTERIC BACTERIA

Oral spirochetes possess many potential virulence factors, including t he capacity for tissue invasion and persistence despite a vigorous hos t immune response. In an attempt to identify treponemal immunoreactive components, sera derived from individuals with advanced periodontal d isease were used as a reagent to isolate recombinant bacteriophage lam bda clones expressing antigens of the oral spirochete Treponema dentic ola ATCC 35405. Nucleotide sequence analysis of a clone expressing thr ee immunoreactive products has revealed seven T. denticola genes which appear to encode homologs of flagellar basal body constituents, FlgB, FlgC, FliE, and FliF, a flagellar switch component, FliG, and the put ative flagellar export proteins, FliH and Flil, initially characterize d in Salmonella typhimurium. Also identified was a gene resembling. Pr imer extension analysis identified a transcriptional start site 5' to the treponemal flgB gene. Appropriately spaced with respect to this st art site was a sigma(28) binding motif. The absence of additional iden tifiable sigma factor binding motifs within the treponemal sequence an d the proximity of adjacent genes suggested operonic arrangement, and reverse transcriptase PCR provided evidence of cotranscription. Suppor ting the identification of these genes as flagellar components, hetero logous expression in enteric bacteria of the putative switch basal bod y genes from T. denticola interfered with motility, Specifically, the presence of a plasmid expressing treponemal fliG reduced swarming moti lity in S. typhimurium, while in Escherichia coli, this plasmid confer red a nonmotile phenotype and a reduction in flagellar number. Thus, w hile spirochetal flagella are subject to unique synthetic and function al constraints, the organization of flagellar genes and the presence o f sigma(28)-like elements are reminiscent of the flagellar systems of other bacteria, and there appears to be sufficient conservation of con stituent proteins to allow interaction between T. denticola switch-bas al body proteins and the flagellar machinery of gram-negative bacteria .