Molecular characterization of a chemotaxis operon in the oral spirochete, Treponema denticola

A chemotaxis gene cluster from Treponema denticola (Td), a pathogenic spirochete associated with human periodontal diseases, was cloned, sequenced, and analyzed. The gene cluster contained three chemotaxis (che) genes (cheA, cheW, and cheY) and an open reading frame (cheX) that is homologous with Treponema pallidum (Tp) and Borrelia burgdorferi (Bb) cheX. The Td che genes have the same transcriptional orientation with a sigma 70-like promoter located upstream of cheA and a stem-loop structure characteristic of a Rho-independent transcriptional terminator downstream of cheY. Primer extension analysis identified a transcriptional start point six nucleotides (nt) downstream of the -10 (TAAAAA) promoter sequence. Reverse-transcriptase-polymerase chain reaction (RT-PCR) data indicated that cheA through cheY are co-transcribed and suggested that transcription is terminated after cheY. The gene organization of the Td che operon is identical to that of the Tp che operon. Southern blot analysis indicated the presence of one copy of each che gene on the Td genome. The cheA, cheW, cheX, and cheY genes are 2403, 1332, 462, and 438nt long, respectively, and encode proteins with predicted molecular masses of 88.2, 49.7, 16.8, and 16. 0kDa, respectively. Functional domains of the T. denticola CheA and CheY proteins are highly conserved with those of the Escherichia coli (Ec) CheA and CheY proteins. Phylogenetic analysis of Td CheY indicated that it is closely related to Tp CheY and Bb CheY3.