Department of Biology, Indiana University Bloomington, Bloomington, Indiana, USA.
Division of Gastroenterology, Department of Medicine, Mayo Clinic, Rochester, Minnesota, USA.
J Bacteriol. 2020 Nov 19;202(24). doi: 10.1128/JB.00261-20.
Motility is required for many bacterial pathogens to reach and colonize target sites. traverses a thick mucus barrier coating the small intestine to reach the underlying epithelium. We screened a transposon library in motility medium containing mucin to identify factors that influence mucus transit. Lesions in structural genes of the type VI secretion system (T6SS) were among those recovered. Two-dimensional (2D) and 3D single-cell tracking was used to compare the motility behaviors of wild-type cells and a mutant that collectively lacked three essential T6SS structural genes (T6SS). In the absence of mucin, wild-type and T6SS cells exhibited similar speeds and run-reverse-flick (RRF) swimming patterns, in which forward-moving cells briefly backtrack before stochastically reorienting (flicking) in a new direction upon resuming forward movement. We show that mucin induced T6SS expression and activity in wild-type bacteria but significantly decreased their swimming speed and flicking, yielding curvilinear or near-surface circular traces for many cells. Conversely, mucin slowed T6SS cells to a lesser extent, and many continued to flick and produce RRF-like traces. Δ cells, which exclusively swim in the forward direction and thus cannot flick, also produced curvilinear traces with or without mucin present and, on occasion, near-surface circular traces in the presence of mucin. The dependence of flicking on swimming speed suggested that mucin-induced T6SS activity further decreased motility and thereby reduced flicking probability during reverse-to-forward transitions. We propose that this encourages cells to continue on their current trajectory rather than reorienting, which may benefit those tracking toward the epithelial surface. deploys an arsenal of virulence factors as it attempts to traverse a protective mucus layer and reach the epithelial surface of the distal small intestine. The T6SS used to cull bacterial competition during infection is induced by mucus. We show that this activity may serve an additional purpose by further decreasing motility in the presence of mucin, thereby reducing the probability of speed-dependent, near-perpendicular directional changes. We posit that this encourages cells to maintain course rather than change direction, which may aid those attempting to reach and colonize the epithelial surface.
运动性是许多细菌病原体到达并定殖靶位所必需的。 穿过覆盖小肠的厚厚的粘液屏障到达下面的上皮细胞。我们在含有粘蛋白的运动培养基中筛选转座子文库，以鉴定影响粘液转运的因素。在回收的突变体中，有一类是属于 VI 型分泌系统（T6SS）的结构基因的突变体。使用二维（2D）和三维单细胞跟踪来比较野生型细胞和缺乏三个必需 T6SS 结构基因（T6SS）的突变体的运动行为。在没有粘蛋白的情况下，野生型和 T6SS 细胞表现出相似的速度和跑-反转-弹（RRF）游泳模式，其中向前移动的细胞在随机重新定向（弹回）之前短暂地向后移动，然后在重新开始向前运动时在新方向上弹回。我们表明，粘蛋白诱导野生型细菌中的 T6SS 表达和活性，但显著降低了它们的游泳速度和弹回，导致许多细胞产生曲线或近表面圆形轨迹。相反，粘蛋白对 T6SS 细胞的减速作用较小，许多细胞继续弹回并产生 RRF 样轨迹。Δ 细胞只能向前游动，因此不能弹回，即使存在粘蛋白，也会产生曲线轨迹，偶尔在存在粘蛋白的情况下也会产生近表面圆形轨迹。弹回与游泳速度的依赖性表明，粘蛋白诱导的 T6SS 活性进一步降低了 运动性，从而降低了反向到正向转变过程中的弹回概率。我们提出，这鼓励细胞继续沿当前轨迹运动，而不是重新定向，这可能有利于那些追踪到上皮表面的细胞。在试图穿过保护性粘液层并到达远端小肠上皮表面时，会部署一系列毒力因子。用于在感染过程中清除细菌竞争的 T6SS 是由粘液诱导的。我们表明，这种活性通过在粘蛋白存在的情况下进一步降低运动性，从而降低与速度相关的近垂直方向变化的概率，可能具有额外的目的。我们假设，这鼓励细胞保持方向而不是改变方向，这可能有助于那些试图到达并定殖上皮表面的细胞。
