细菌等微生物在人体中生活在由蛋白质、多糖等大分子构成的拥挤环境中。同时，细菌趋于在界面积聚，个体之间的相互作用显著，相应的三维交互行为(靠近、接触、碰撞等) 频繁发生。因此，它们在该环境下的近界面的相互作用决定它们的行为，进而影响其生存和繁殖。然而，传统的显微技术在该环境下会出现影像重叠，无法观察这些三维行为。目前由于缺乏有效的观测手段，研究微生物在大分子环境下的相互作用十分具有挑战性。在本项目中，我们将利用数字全息显微镜对大分子浓溶液中多个细菌的近界面运动进行实时三维追踪。针对个体间相互作用导致的轨迹中断，我们将建立续连算法，引入三维运动矢量和形貌判据，恢复多个个体的轨迹片段，还原细菌从远离、靠近、接触至附着/再分离的三维交互行为。此外，我们将研究大分子组分、浓度和流变性能对相互作用的影响，深入了解这类微生物的生存机制。

Actively swimming bacteria live in human body, a circumstance crowded with macromolecules and biointerfaces. Swimming bacteria tends to accumulate near the biointerfaces, giving raise to frequent interactions between individuals. Consequently, the near-surface dynamics, especially the interactions between bacteria in macromolecular crowded environment determines their survival and colonization. However, two-dimensional optical techniques fail to track the cell interactions as the cells become denser due to the image overlapping. Therefore, monitoring the near-surface dynamics of bacteria at a high density in macromolecular crowded environment still remains a challenge. In this proposal, utilizing digital holographic microscopy (DHM) which reconstructs the three-dimensional (3D) trajectories of multiple objects with a high spatial resolution (hundreds of nm), we will track the near-surface dynamics of bacteria in macromolecular solutions. In particular, we will develop algorithms for identifying and connecting discontinued 3D trajectory segments. This algorithm will be appied to evaluate the interactive behaviors of bacteria in different biomacromolecular solutions. The outcome of this research will help a better understanding for the bacteria behaviors in real situations.