Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan, USA.
Environ Microbiol. 2022 Oct;24(10):4738-4754. doi: 10.1111/1462-2920.16193. Epub 2022 Sep 15.
Erwinia amylovora, the causative agent of fire blight, uses flagella-based motilities to translocate to host plant natural openings; however, little is known about how this bacterium migrates systemically in the apoplast. Here, we reveal a novel surface motility mechanism, defined as sliding, in E. amylovora. Deletion of flagella assembly genes did not affect this movement, whereas deletion of biosynthesis genes for the exopolysaccharides (EPSs) amylovoran and levan resulted in non-sliding phenotypes. Since EPS production generates osmotic pressure that potentially powers sliding, we validated this mechanism by demonstrating that water potential positively contributes to sliding. In addition, no sliding was observed when the water potential of the surface was lower than -0.5 MPa. Sliding is a passive motility mechanism. We further show that the force of gravity plays a critical role in directing E. amylovora sliding on unconfined surfaces but has a negligible effect when cells are sliding in confined microcapillaries, in which EPS-dependent osmotic pressure acts as the main force. Although amylovoran and levan are both required for sliding, we demonstrate that they exhibit different roles in bacterial communities. In summary, our study provides fundamental knowledge for a better understanding of mechanisms that drive bacterial sliding motility.
果胶杆菌，火疫病的病原体，利用鞭毛运动将自身转移到宿主植物的天然开口处；然而，对于这种细菌如何在植物细胞外质中系统性地迁移，我们知之甚少。在这里，我们揭示了果胶杆菌中一种新的表面运动机制，称为滑动。鞭毛组装基因的缺失不影响这种运动，而多糖（EPS）果胶糖和纤维二糖生物合成基因的缺失则导致非滑动表型。由于 EPS 的产生会产生渗透压，从而为滑动提供动力，因此我们通过证明水势对滑动有积极贡献来验证了这一机制。此外，当表面的水势低于-0.5 MPa 时，也观察不到滑动。滑动是一种被动的运动机制。我们进一步表明，重力的作用在指导果胶杆菌在无约束表面上滑动方面起着关键作用，但当细胞在受 EPS 依赖的渗透压作用的受限微管中滑动时，这种作用可以忽略不计。虽然果胶糖和纤维二糖都对滑动有要求，但我们证明它们在细菌群落中发挥不同的作用。总之，我们的研究为更好地理解推动细菌滑动运动的机制提供了基础知识。
