Biochemical and genetic characterization of the flagellar filaments from the rumen anaerobe Butyrivibrio fibrisolvens OR77

Flagellar filaments isolated from stationary phase cells of the rumen anaerobe Butyrivibrio fibrisolvens OR77 were composed of three flagellins (54, 62 and 68kDa). All three proteins demonstrated a conserved N-terminus, with homology to the N-terminus of the flagellin from the intestinal anaerobe Roseburia cecicola. Two genes encoding flagellins were identified and cloned from the genome of this isolate. Transcriptional analysis indicated that both genes were expressed, but as separate unit length messages. The first gene (flaA) encoded a flagellin with a predicted molecular weight of 50 kDa. Transcription initiation within the flaA operon occured at two different promoter sites. The first promoter demonstrated significant sequence similarity to the flagellum specific promoter consensus sequence (sigma(28)), the second to the general "housekeeping" consensus sequence (sigma(43)). The second flagellin gene (flaB) encoded a flagellin with a predicted molecular weight of 54 kDa. Differences in the predicted and determined flagellin molecular weights, the number of flagellins and corresponding genes, and a positive reaction using an immunoassay for the detection of digoxigenin labeled sugars, indicate that the flagellins of B. fibrisolvens OR77 undergo post-translational modification in the form of glycosylation.