Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, AB T2N1N4, Canada.
BMC Microbiol. 2010 Aug 17;10:219. doi: 10.1186/1471-2180-10-219.
Rhizobium leguminosarum bv. viciae establishes symbiotic nitrogen fixing partnerships with plant species belonging to the Tribe Vicieae, which includes the genera Vicia, Lathyrus, Pisum and Lens. Motility and chemotaxis are important in the ecology of R. leguminosarum 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.
R. leguminosarum strains 3841 and VF39SM have seven flagellin genes (flaA, flaB, flaC, flaD, flaE, flaH, and flaG), which are transcribed separately. The predicted flagellins of 3841 are highly similar or identical to the corresponding flagellins in VF39SM. flaA, flaB, flaC, and flaD are in tandem array and are located in the main flagellar gene cluster. flaH and flaG are located outside of the flagellar/motility region while flaE 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 flaA resulted in non-motile VF39SM and extremely reduced motility in 3841. Individual mutations of flaB and flaC resulted in shorter flagellar filaments and consequently reduced swimming and swarming motility for both strains. Mutant VF39SM strains carrying individual mutations in flaD, flaE, flaH, and flaG were not significantly affected in motility and filament morphology. The flagellar filament and the motility of 3841 strains with mutations in flaD and flaG were not significantly affected while flaE and flaH mutants exhibited shortened filaments and reduced swimming motility.
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 R. leguminosarum 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.
根瘤菌属豌豆根瘤菌与属于 Vicieae 部落的植物物种建立共生固氮伙伴关系，其中包括 Vicia、Lathyrus、Pisum 和 Lens 属。运动性和趋化性在根瘤菌属豌豆根瘤菌的生态学中很重要，可为早期结瘤提供竞争优势，但运动性和鞭毛组装的机制仍研究甚少。本文研究了七个鞭毛蛋白基因在产生功能鞭毛中的作用。
根瘤菌属菌株 3841 和 VF39SM 有七个鞭毛蛋白基因（flaA、flaB、flaC、flaD、flaE、flaH 和 flaG），它们分别转录。3841 的预测鞭毛蛋白与 VF39SM 的相应鞭毛蛋白高度相似或相同。flaA、flaB、flaC 和 flaD 串联排列，位于主要鞭毛基因簇中。flaH 和 flaG 位于鞭毛/运动区域之外，而 flaE 则位于质粒上。五个鞭毛蛋白亚基（FlaA、FlaB、FlaC、FlaE 和 FlaG）彼此高度相似，而 FlaD 和 FlaH 则更为相关。所有鞭毛蛋白在 N 和 C 末端都具有保守的氨基酸残基，而在中心区域则具有可变的氨基酸残基。菌株 3841 具有 1-3 根普通的亚极鞭毛，而菌株 VF39SM 则具有 4-7 根普通的周生鞭毛。通过质谱法在菌株 3841 和 VF39SM 的鞭毛丝中分别检测到三种鞭毛蛋白（FlaA/B/C）和五种鞭毛蛋白（FlaA/B/C/E/G）。flaA 的突变导致 VF39SM 失去运动性，而 3841 的运动性大大降低。flaB 和 flaC 的单个突变导致鞭毛丝变短，从而降低了两种菌株的泳动和群集运动能力。flaD、flaE、flaH 和 flaG 单个突变的突变株 VF39SM 在运动性和丝状体形态上没有受到明显影响。flaD 和 flaG 突变株 3841 的鞭毛丝和运动性没有受到明显影响，而 flaE 和 flaH 突变株的鞭毛丝变短，泳动能力降低。
本研究结果表明，FlaA、FlaB 和 FlaC 是菌株 3841 和 VF39SM 鞭毛丝的主要成分，而 FlaD 和 FlaG 是次要成分。我们还观察到两株菌株之间存在差异，其中 FlaE 和 FlaH 似乎是 VF39SM 鞭毛丝的次要成分，但这些鞭毛蛋白在 3841 中可能发挥更重要的作用。本文还表明，3841 和 VF39SM 的鞭毛蛋白可能被糖基化。
