购彩中心

TOPIC：Mechanical Principles of Biofilm Formation（细菌菌膜形成的力学机制）
SPEAKER：Dr. Jing Yan, Princeton University（严兢博士，普林斯顿大学）

TIME: May 24 (Wednesday) 10:00 am
LOCATION：Room 410, Chemistry Building B （化学B楼410室）
INVITER：Prof. Xinyuan Zhu, Prof. Yongfeng Zhou（朱新远教授，周永丰教授）        

ABSTRACT
Biofilms are surface-associated bacterial communities embedded in an extracellular matrix. Biofilm cells are a major problem in the context of chronic infections, because biofilm dwelling cells have increased antibiotic resistance compared to their planktonic counterparts. Investigations so far have mainly focused on the genetic and regulatory features driving biofilm formation. However, still lacking is a fundamental biophysical and biomechanical understanding of how bacteria, in time and space, build these dense three-dimensional structures.

During this talk, I will discuss about our recently progress in using Vibrio cholerae as a model biofilm former to reveal the mechanical principles behind biofilm formation. I will first present a new methodology to image living, growing bacterial biofilms at single-cell resolution, and demonstrate how cell-cell adhesion and cell-surface adhesion balance each other to cause V. cholerae biofilms to transition from a two-dimensional branched morphology to an ordered three-dimensional cluster. Next, I will demonstrate how matrix production enables biofilm cells to establish an osmotic pressure differential between the biofilm and the external environment, and use this osmotic pressure to facilitate the biofilm expansion. Finally, I will present various mechanical instabilities that takes place when biofilms grow on soft tissue-like substrates. We also complemented these mechanical studies by genetic analyses and ecological competition experiments to decipher the biological consequences of the biomechanical phenomena observed in bacterial biofilms.

   细菌菌膜是细菌依附于各种表面，由细胞外基质包裹而成的团簇。菌膜引起的慢性病很难根治，因为菌膜中的细菌相比于浮游的细菌更具有抗药性。至今为止的大多数研究侧重于导致菌膜形成的基因及其调控机制，然而我们仍缺少从生物物理和生物力学角度对于菌膜形成机理的理解。

   在这个报告中，我会讨论我们近期以弧形霍乱菌为模型生物，从生物力学角度对菌膜形成的研究进展。首先，我们发展了一种成像技术使得我们能够在单细胞水平上实时原位观察菌膜形成的过程。我们发现细菌之间的结合力和细菌与表面的结合力之间的平衡使得菌膜能够完成从枝状的二维结构向紧密有序堆积的三维结构的转变。其次，我们发现菌膜中的细菌通过分泌细胞外基质而建立渗透压梯度，从而获取养分并帮助其在表面上扩展。最后，我会讨论当菌膜在不同的柔性表面上形成时所发生的力学失稳现象。通过对不同菌种的表征和竞争实验，我们进一步分析了以上力学机理对于菌膜在自然生态环境中的影响。

Short Bio:
Dr. Jing Yan obtained his bachelor degree in the College of Chemistry and Molecular Engineering in Peking University. As a graduate student, he studied soft matter physics in the Department of Materials Science and Engineering at University of Illinois at Urbana-Champaign. During his Ph.D., he developed a series of nonequilibrium colloidal materials driven by external electromagnetic fields. He then transitioned to biology, working at Princeton jointly in the Department of Molecular Biology and Mechanical Engineering, on understanding the formation of bacterial biofilms. He has published a series of research papers in journals including Nature and Nature Materials, and he is now a Burroughs Wellcome Fellow working at the interface between biology and engineering.

   严兢博士本科毕业于北京大学化学与分子工程学院。博士期间，他就读于伊利诺伊大学香槟分校的材料科学与工程系，专攻软物质物理。在博士期间，他发展了一系列由外场驱动的非平衡态胶体材料。博士毕业后，他转向生物方向并就职于普利斯顿大学的分子生物系与机械工程系，主要研究方向为细菌菌膜的形成与治理。在博士及博士后期间，其曾在自然，自然材料等杂志上发表文章，并获得2016年度美国Burroughs Wellcome基金会的交叉学科成就奖。