EXPRESSION OF THE FLAGELLIN GENE IN BORRELIA IS CONTROLLED BY AN ALTERNATIVE SIGMA-FACTOR

The flagellin genes from six Borrelia species were cloned, sequenced a nd characterized at the molecular level. The flagellin genes of two re lapsing fever Borrelia species, B. hermsii and B. crocidurae, three Ly me disease genomic species, B. burgdorferi, B. afzelii and B. garinii, and the avian borreliosis agent, B. anserina, were compared and showe d an 85-93 % sequence identity to each other. Comparison of the fla ge nes from the different Lyme borreliosis spirochaetes revealed that the y were 94-99 % identical. Nucleotide sequencing of the fla gene and pr imer extension on isolated mRNA from both B. hermsii (as transcribed i n Escherichia coli) and B. burgdorferi (as transcribed in the natural host) identified the putative transcriptional start points, the riboso me binding sites and the promoter regions of these genes. The deduced promoter of the Borrelia flagellin gene resembled neither the sigma(70 ) promoter of prokaryotes, as seen for the genes for the outer-surface proteins A and B in Lyme disease Borrelia and the genes for the varia ble major proteins 7 and 21 of a. hermsii, nor the sigma(28) consensus promoter region of motility genes from other bacteria. Instead, the p romoter of the fla gene in Borrelia has most similarity to the bacteri ophage SPO1 sigma(gp33-34) promoter sequence of Bacillus subtilis.