Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
School of Physics and Astronomy, The University of Edinburgh, Edinburgh, United Kingdom.
PLoS Biol. 2024 Feb 13;22(2):e3002488. doi: 10.1371/journal.pbio.3002488. eCollection 2024 Feb.
Bacteria live in social communities, where the ability to sense and respond to interspecies and environmental signals is critical for survival. We previously showed the pathogen Pseudomonas aeruginosa detects secreted peptides from bacterial competitors and navigates through interspecies signal gradients using pilus-based motility. Yet, it was unknown whether P. aeruginosa utilizes a designated chemosensory system for this behavior. Here, we performed a systematic genetic analysis of a putative pilus chemosensory system, followed by high-speed live-imaging and single-cell tracking, to reveal behaviors of mutants that retain motility but are blind to interspecies signals. The enzymes predicted to methylate (PilK) and demethylate (ChpB) the putative pilus chemoreceptor, PilJ, are necessary for cells to control the direction of migration. While these findings implicate PilJ as a bona fide chemoreceptor, such function had yet to be experimentally defined, as full-length PilJ is essential for motility. Thus, we constructed systematic genetic modifications of PilJ and found that without the predicted ligand binding domains or predicted methylation sites, cells lose the ability to detect competitor gradients, despite retaining pilus-mediated motility. Chemotaxis trajectory analysis revealed that increased probability and size of P. aeruginosa pilus-mediated steps towards S. aureus peptides, versus steps away, determines motility bias in wild type cells. However, PilJ mutants blind to interspecies signals take less frequent steps towards S. aureus or steps of equal size towards and away. Collectively, this work uncovers the chemosensory nature of PilJ, provides insight into how cell movements are biased during pilus-based chemotaxis, and identifies chemotactic interactions necessary for bacterial survival in polymicrobial communities, revealing putative pathways where therapeutic intervention might disrupt bacterial communication.
细菌生活在社会群体中，它们能够感知和响应种间和环境信号，这对于生存至关重要。我们之前曾表明，病原体铜绿假单胞菌能够检测到来自细菌竞争者的分泌肽，并利用菌毛运动来导航种间信号梯度。然而，尚不清楚铜绿假单胞菌是否利用专门的化学感觉系统来进行这种行为。在这里，我们对一个假定的菌毛化学感觉系统进行了系统的遗传分析，然后进行高速活细胞成像和单细胞跟踪，以揭示保留运动能力但对种间信号视而不见的突变体的行为。预测甲基化（PilK）和去甲基化（ChpB）假定菌毛感受器 PilJ 的酶对于细胞控制迁移方向是必要的。虽然这些发现表明 PilJ 是一种真正的化学感受器，但这种功能尚未通过实验来定义，因为全长 PilJ 对于运动是必不可少的。因此，我们构建了 PilJ 的系统遗传修饰，并发现没有预测的配体结合结构域或预测的甲基化位点，即使保留菌毛介导的运动，细胞也会失去检测竞争梯度的能力。趋化轨迹分析表明，铜绿假单胞菌对金黄色葡萄球菌肽的 PilJ 介导的趋化运动的概率和大小增加，与远离的运动相比，决定了野生型细胞的运动偏向。然而，对种间信号视而不见的 PilJ 突变体对金黄色葡萄球菌的趋化运动的频率降低，或者向金黄色葡萄球菌和远离金黄色葡萄球菌的运动步幅相等。总的来说，这项工作揭示了 PilJ 的化学感觉特性，深入了解了在菌毛依赖的趋化作用中如何使细胞运动偏向，并且确定了在多微生物群落中细菌生存所必需的趋化相互作用，揭示了潜在的治疗干预可能破坏细菌通信的途径。
