The Campylobacter sigma 54 flaB flagellin promoter is subject to environmental regulation

The complex flagellum of Campylobacter coli VC167 is encoded by two tandemly oriented flagellin genes which are transcribed as two discrete transcriptional units from two different classes of promoters. The flaB gene, which encodes the minor FlaB filament protein, is controlled by a sigma 54 promoter. A transcriptional fusion between a promoterless chloramphenicol acetyltransferase (CAT) reporter gene cartridge and C. coli VC167 DNA carrying flaB transcription and translation signals, including the typical position -13-to-(-)26 flaB sigma 54 consensus promoter sequence, was constructed. When carried on plasmid pRIC1013, the sigma 54-CAT fusion expressed chloramphenicol resistance in Escherichia coli, and CAT production was affected by the pH of the growth medium, the composition of the growth atmosphere, and the growth temperature, with production being significantly higher at 42 degrees C. A conjugative suicide vector, pRIC1028, containing the sigma 54-CAT fusion was constructed and used to recombine the flaB-CAT fusion back into the C. coli chromosome in the correct position with respect to the flaA gene and its transcription terminator. CAT production from the flaB sigma 54 promoter in the C. coli transconjugant VC167-T2/28-1 was shown to peak at mid-log phase and to be modulated by growth medium pH, growth temperature, and the concentration of certain inorganic salts and divalent cations in the growth medium. Under growth conditions which promoted elevated flaB sigma 54 promoter activity, a flaA flaB+ mutant of C. coli VC167 produced increased amounts of FlaB flagellar protein and displayed increased motility.