Thomas Wendy E, Nilsson Lina M, Forero Manu, Sokurenko Evgeni V, Vogel Viola
Department of Bioengineering, University of Washington, Seattle, WA, 98195, USA.
Mol Microbiol. 2004 Sep;53(5):1545-57. doi: 10.1111/j.1365-2958.2004.04226.x.
It is generally assumed that bacteria are washed off surfaces as fluid flow increases because they adhere through 'slip-bonds' that weaken under mechanical force. However, we show here that the opposite is true for Escherichia coli attachment to monomannose-coated surfaces via the type 1 fimbrial adhesive subunit, FimH. Raising the shear stress (within the physiologically relevant range) increased accumulation of type 1 fimbriated bacteria on monomannose surfaces by up to two orders of magnitude, and reducing the shear stress caused them to detach. In contrast, bacterial binding to anti-FimH antibody-coated surfaces showed essentially the opposite behaviour, detaching when the shear stress was increased. These results can be explained if FimH is force-activated; that is, that FimH mediates 'catch-bonds' with mannose that are strengthened by tensile mechanical force. As a result, on monomannose-coated surfaces, bacteria displayed a complex 'stick-and-roll' adhesion in which they tended to roll over the surface at low shear but increasingly halted to stick firmly as the shear was increased. Mutations in FimH that were predicted earlier to increase or decrease force-induced conformational changes in FimH were furthermore shown here to increase or decrease the probability that bacteria exhibited the stationary versus the rolling mode of adhesion. This 'stick-and-roll' adhesion could allow type 1 fimbriated bacteria to move along mannosylated surfaces under relatively low flow conditions and to accumulate preferentially in high shear regions.
一般认为，随着流体流速增加，细菌会从表面被冲走，因为它们通过在机械力作用下会减弱的“滑动键”附着在表面。然而，我们在此表明，对于大肠杆菌通过1型菌毛粘附亚基FimH附着于单甘露糖包被的表面而言，情况恰恰相反。提高剪切应力（在生理相关范围内）会使1型菌毛化细菌在单甘露糖表面的积累增加多达两个数量级，而降低剪切应力则会导致它们脱离。相比之下，细菌与抗FimH抗体包被表面的结合表现出基本相反的行为，即当剪切应力增加时会脱离。如果FimH是力激活的，那么这些结果就可以得到解释；也就是说，FimH介导与甘露糖的“捕获键”，这种键会因拉伸机械力而增强。因此，在单甘露糖包被的表面上，细菌表现出一种复杂的“粘-滚”粘附，即在低剪切力下它们倾向于在表面滚动，但随着剪切力增加，它们会越来越多地停下来并牢固地粘附。在此还表明，先前预测会增加或减少FimH中力诱导构象变化的FimH突变，会增加或降低细菌表现出静止粘附模式与滚动粘附模式的概率。这种“粘-滚”粘附可以使1型菌毛化细菌在相对低流量条件下沿着甘露糖化表面移动，并优先在高剪切区域积累。
