We present an experimental study combining particle tracking, active microrheology, and differential dynamic microscopy (DDM) to investigate the dynamics and rheology of an oil–water interface during biofilm formation by the bacteria Pseudomonas Aeruginosa PA14. The interface transitions from an active fluid dominated by the swimming motion of adsorbed bacteria at early age to an active viscoelastic system at late ages when the biofilm is established. The microrheology measurements using microscale magnetic rods indicate that the biofilm behaves as a viscoelastic solid at late age. The bacteria motility at the interface during the biofilm formation, which is characterized in the DDM measurements, evolves from diffusive motion at early age to constrained, quasi-localized motion at later age. Similarly, the mobility of passively moving colloidal spheres at the interface decreases significantly with increasing interface age and shows a dependence on sphere size after biofilm formation that is orders-of-magnitude larger than that expected in a homogeneous system in equilibrium. We attribute this anomalous size dependence to either length-scale-dependent rheology of the biofilm or widely differing effects of the bacteria activity on the motion of spheres of different sizes.

中文翻译：

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细菌生物膜形成过程中油水界面的动态和机械演化

我们提出了一项结合粒子追踪、主动微流变学和微分动态显微镜 (DDM) 的实验研究，以研究铜绿假单胞菌生物膜形成过程中油水界面的动力学和流变学PA14。当生物膜建立时，界面从早期由吸附细菌的游泳运动主导的活跃流体转变为晚期活跃的粘弹性系统。使用微型磁棒进行的微流变学测量表明，生物膜在晚年表现为粘弹性固体。生物膜形成过程中界面处的细菌运动，在 DDM 测量中具有特征，从早期的扩散运动演变为晚期的受约束的准局部运动。类似地，界面处被动移动胶体球的流动性随着界面年龄的增加而显着降低，并且在生物膜形成后显示出对球体大小的依赖性，该大小比在平衡的均质系统中预期的大几个数量级。