Biofilms exist in complex environments, including the intestinal tract, as a part of the gastrointestinal microbiota. The interaction of planktonic bacteria with biofilms can be influenced by material properties of the biofilm. During previous confocal studies, we observed that amyloid curli-containing Salmonella enterica serotype Typhimurium and Escherichia coli biofilms appeared rigid. In these studies, Enterococcus faecalis, which lacks curli-like protein, showed more fluid movement. To better characterize the material properties of the biofilms, a four-dimensional (4D) model was designed to track the movement of 1-μm glyoxylate beads in 10- to 20-μm-thick biofilms over approximately 20 min using laser-scanning confocal microscopy. Software was developed to analyze the bead trajectories, the amount of time they could be followed (trajectory life span), the velocity of movement, the surface area covered (bounding boxes), and cellular density around each bead. Bead movement was found to be predominantly Brownian motion. Curli-containing biofilms had very little bead movement throughout the low- and high-density regions of the biofilm compared to E. faecalis and isogenic curli mutants. Curli-containing biofilms tended to have more stable bead interactions (longer trajectory life spans) than biofilms lacking curli. In biofilms lacking curli, neither the velocity of bead movement nor the bounding box volume was strictly dependent on cell density, suggesting that other material properties of the biofilms were influencing the movement of the beads and flexibility of the material. Taken together, these studies present a 4D method to analyze bead movement over time in a 3D biofilm and suggest curli confers rigidity to the extracellular matrix of biofilms.

中文翻译：

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基于珠子运动的新计算框架的开发表明细菌淀粉样蛋白 Curli 降低了生物膜中的珠子流动性。

生物膜存在于复杂的环境中，包括肠道，作为胃肠道微生物群的一部分。浮游细菌与生物膜的相互作用会受到生物膜材料特性的影响。在之前的共聚焦研究中，我们观察到含有淀粉样蛋白 curli 的肠沙门氏菌血清型鼠伤寒和大肠杆菌生物膜显得僵硬。在这些研究中，粪肠球菌，缺乏类似卷曲的蛋白质，表现出更多的流体运动。为了更好地表征生物膜的材料特性，设计了一个四维 (4D) 模型，使用激光扫描共聚焦显微镜在大约 20 分钟内跟踪 1 μm 乙醛酸盐珠在 10 至 20 μm 厚的生物膜中的运动. 开发了软件来分析珠子轨迹、它们可以遵循的时间量（轨迹寿命）、运动速度、覆盖的表面积（边界框）以及每个珠子周围的细胞密度。发现珠粒运动主要是布朗运动。与粪肠球菌相比，含有 Curli 的生物膜在生物膜的低密度和高密度区域几乎没有珠子运动和等基因 curli 突变体。含有 Curli 的生物膜往往比缺乏 curli 的生物膜具有更稳定的珠子相互作用（更长的轨迹寿命）。在缺少 curli 的生物膜中，珠子运动的速度和边界框体积都不严格依赖于细胞密度，这表明生物膜的其他材料特性正在影响珠子的运动和材料的柔韧性。综上所述，这些研究提出了一种 4D 方法来分析珠子在 3D 生物膜中随时间的运动，并表明 curli 赋予生物膜的细胞外基质刚性。