A flagellar gene cluster from the oral spirochaete Treponema maltophilum

A flagellar gene cluster from the oral spirochaete Treponema maltophilum ATCC 51939T was cloned. Sequence analysis revealed six putative ORFs, two of which encode the flagellar subunit proteins FlaB2 (286 aa) and FlaB3 (285 aa). Northern blot analysis revealed two flagellin transcripts with the expected size of monocistronic mRNAs. Sequence analysis and primer extension experiments indicated that the transcription of the flaB2 gene is directed by a sigma28-like FliA factor. Using fliA and fliA+ Escherichia coli K-12 strains, it was shown that flaB2 expression in E. coli required the sigma28 factor using an initiation site identical to that in Treponema maltophilum. Primer extension analysis revealed two transcriptional start sites 5' of the flaB3 gene, a strong promoter with a sigma28-like -10 promoter element and a weak promoter with a putative sigma54 promoter consensus sequence. Downstream of flaB3, a putative fliD homologue was found, probably encoding the flagellar cap protein of Treponema maltophilum. Flagellin-gene-specific DNA probes hybridized to all 13 Treponema strains investigated, whereas a fliD-specific DNA probe only hybridized to Treponema maltophilum, other treponemal group IV isolates and Treponema brennaborense.