Laboratory of Food and Environmental Microbiology, Earth and Life Institute, Université catholique de Louvain, Croix du Sud 2, Box L7.05.12, B-1348 Louvain-la-Neuve, Belgium.
Micron. 2012 Dec;43(12):1304-11. doi: 10.1016/j.micron.2012.01.014. Epub 2012 Feb 8.
Swarming motility is a fascinating phenomenon by which some bacteria use flagella to move over solid surfaces. Understanding the molecular mechanisms underlying swarming motility requires studying the factors that induce and control flagella expression in swarming cells. Traditionally, flagella are observed by optical or electron microscopy, but none of these techniques combine versatility and easiness, with quantitative and high-resolution information. We report an atomic force microscopy (AFM)-based approach for the fast imaging of bacterial phenotypes (cell shape, flagella expression) in swarming motility studies. Cells from the gram-positive bacterium Bacillus thuringiensis sv. israelensis were inoculated on energy-rich media containing increasing agar concentrations. Following swarming assays (2 days), the cell morphology and the amount of flagella were directly observed by AFM imaging in air. Consistent with the macroscopic swarming behavior, cells harvested from the rim of colonies spreading on soft agar were hyperflagellated, elongated and arranged in chains. Increasing the agar concentration led to much lower amounts of flagella and to shorter rod-shaped cells, a finding consistent with the slower swarming motility of the cells. Cells taken from colony centers on soft and hard agar surfaces were generally non-flagellated, rod-shaped, rarely arranged in chains, and exhibited lysis and sporulation. This study shows that AFM imaging can readily discriminate between swarming and non-swarming cells, and quantify their morphological details, thus offering an important tool to study the dynamics of bacterial populations.
群体运动是一种迷人的现象，一些细菌利用鞭毛在固体表面上移动。理解群体运动背后的分子机制需要研究诱导和控制群体运动细胞中鞭毛表达的因素。传统上，通过光学或电子显微镜观察鞭毛，但这些技术都没有将多功能性和易用性与定量和高分辨率信息结合起来。我们报告了一种基于原子力显微镜（AFM）的方法，用于快速成像细菌表型（细胞形状、鞭毛表达）在群体运动研究中。将革兰氏阳性菌苏云金芽孢杆菌 sv 的细胞接种在含有琼脂浓度逐渐增加的富含能量的培养基上。在进行群体运动实验（2 天）后，通过 AFM 成像在空气中直接观察细胞形态和鞭毛数量。与宏观群体运动行为一致，从在软琼脂上扩散的菌落边缘收获的细胞表现出超鞭毛、伸长和链状排列。随着琼脂浓度的增加，鞭毛数量显著减少，杆状细胞变短，这与细胞群体运动速度变慢的情况一致。从软琼脂和硬琼脂表面的菌落中心采集的细胞通常无鞭毛，呈杆状，很少排列成链状，并且表现出裂解和孢子形成。这项研究表明，AFM 成像可以轻易区分群体运动和非群体运动的细胞，并定量它们的形态细节，因此为研究细菌群体的动态提供了一个重要工具。
