Characterization and functional analysis of seven flagellin genes in <it>Rhizobium leguminosarum </it>bv. <it>viciae</it>. Characterization of <it>R. leguminosarum </it>flagellins

• Main Authors: Tambalo Dinah D, Bustard Denise E, Del Bel Kate L, Koval Susan F, Khan Morgan F, Hynes Michael F
• Format: Article
• Language: English
• Published: BMC 2010-08-01
• Series: BMC Microbiology
• Online Access: http://www.biomedcentral.com/1471-2180/10/219

<p>Abstract</p> <p>Background</p> <p><it>Rhizobium leguminosarum </it>bv. <it>viciae </it>establishes symbiotic nitrogen fixing partnerships with plant species belonging to the Tribe Vicieae, which includes the genera <it>Vicia, Lathyrus, Pisum </it>and <it>Lens</it>. Motility and chemotaxis are important in the ecology of <it>R. leguminosarum </it>to provide a competitive advantage during the early steps of nodulation, but the mechanisms of motility and flagellar assembly remain poorly studied. This paper addresses the role of the seven flagellin genes in producing a functional flagellum.</p> <p>Results</p> <p><it>R. leguminosarum </it>strains 3841 and VF39SM have seven flagellin genes (<it>flaA</it>, <it>flaB, flaC, flaD, flaE, flaH</it>, and <it>flaG</it>), which are transcribed separately. The predicted flagellins of 3841 are highly similar or identical to the corresponding flagellins in VF39SM. <it>flaA, flaB, flaC</it>, and <it>flaD </it>are in tandem array and are located in the main flagellar gene cluster. <it>flaH </it>and <it>flaG </it>are located outside of the flagellar/motility region while <it>flaE </it>is plasmid-borne. Five flagellin subunits (FlaA, FlaB, FlaC, FlaE, and FlaG) are highly similar to each other, whereas FlaD and FlaH are more distantly related. All flagellins exhibit conserved amino acid residues at the N- and C-terminal ends and are variable in the central regions. Strain 3841 has 1-3 plain subpolar flagella while strain VF39SM exhibits 4-7 plain peritrichous flagella. Three flagellins (FlaA/B/C) and five flagellins (FlaA/B/C/E/G) were detected by mass spectrometry in the flagellar filaments of strains 3841 and VF39SM, respectively. Mutation of <it>flaA </it>resulted in non-motile VF39SM and extremely reduced motility in 3841. Individual mutations of <it>flaB </it>and <it>flaC </it>resulted in shorter flagellar filaments and consequently reduced swimming and swarming motility for both strains. Mutant VF39SM strains carrying individual mutations in <it>flaD, flaE, flaH</it>, and <it>flaG </it>were not significantly affected in motility and filament morphology. The flagellar filament and the motility of 3841 strains with mutations in <it>flaD </it>and <it>flaG </it>were not significantly affected while <it>flaE </it>and <it>flaH </it>mutants exhibited shortened filaments and reduced swimming motility.</p> <p>Conclusion</p> <p>The results obtained from this study demonstrate that FlaA, FlaB, and FlaC are major components of the flagellar filament while FlaD and FlaG are minor components for <it>R. leguminosarum </it>strains 3841 and VF39SM. We also observed differences between the two strains, wherein FlaE and FlaH appear to be minor components of the flagellar filaments in VF39SM but these flagellin subunits may play more important roles in 3841. This paper also demonstrates that the flagellins of 3841 and VF39SM are possibly glycosylated.</p>