Department of Mechanical Engineering, University of Vermont, Burlington, VT, United States of America.
PLoS One. 2020 Dec 8;15(12):e0243280. doi: 10.1371/journal.pone.0243280. eCollection 2020.
Gram-negative bacteria, as well as some Gram-positive bacteria, possess hair-like appendages known as fimbriae, which play an important role in adhesion of the bacteria to surfaces or to other bacteria. Unlike the sex pili or flagellum, the fimbriae are quite numerous, with of order 1000 fimbriae appendages per bacterial cell. In this paper, a recently developed hybrid model for bacterial biofilms is used to examine the role of fimbriae tension force on the mechanics of bacterial biofilms. Each bacterial cell is represented in this model by a spherocylindrical particle, which interact with each other through collision, adhesion, lubrication force, and fimbrial force. The bacterial cells absorb water and nutrients and produce extracellular polymeric substance (EPS). The flow of water and EPS, and nutrient diffusion within these substances, is computed using a continuum model that accounts for important effects such as osmotic pressure gradient, drag force on the bacterial cells, and viscous shear. The fimbrial force is modeled using an outer spherocylinder capsule around each cell, which can transmit tensile forces to neighboring cells with which the fimbriae capsule collides. We find that the biofilm structure during the growth process is dominated by a balance between outward drag force on the cells due to the EPS flow away from the bacterial colony and the inward tensile fimbrial force acting on chains of cells connected by adhesive fimbriae appendages. The fimbrial force also introduces a large rotational motion of the cells and disrupts cell alignment caused by viscous torque imposed by the EPS flow. The current paper characterizes the competing effects of EPS drag and fimbrial force using a series of computations with different values of the ratio of EPS to bacterial cell production rate and different numbers of fimbriae per cell.
革兰氏阴性菌和一些革兰氏阳性菌都拥有一种称为菌毛的毛发状附属物，它在细菌黏附于表面或其他细菌方面起着重要作用。与性菌毛或鞭毛不同，菌毛数量众多，每个细菌细胞大约有 1000 个菌毛附属物。在本文中，使用最近开发的细菌生物膜混合模型来研究菌毛张力对细菌生物膜力学的作用。在该模型中，每个细菌细胞由一个球柱形颗粒表示，通过碰撞、黏附、润滑和菌毛力相互作用。细菌细胞吸收水分和营养物质并产生细胞外聚合物质（EPS）。使用连续体模型计算水和 EPS 的流动以及这些物质内的营养物质扩散，该模型考虑了渗透压梯度、细菌细胞上的阻力以及粘性剪切等重要影响。菌毛力使用围绕每个细胞的外球柱形胶囊来建模，它可以将拉伸力传递到与菌毛胶囊碰撞的相邻细胞。我们发现，在生长过程中，生物膜结构主要由 EPS 从细菌菌落流出导致的细胞向外阻力和作用于通过黏附菌毛附属物连接的细胞链的向内拉伸菌毛力之间的平衡来决定。菌毛力还会引起细胞的大旋转运动，并破坏由 EPS 流动引起的粘性扭矩导致的细胞对齐。本文使用不同 EPS 与细菌细胞产生速率比和每个细胞不同菌毛数的一系列计算来描述 EPS 阻力和菌毛力的竞争作用。
