Probing Cell Wall Synthetic Dynamics by Bacterial Flagellar Motor in Escherichia coli

• Main Authors: Yi-Jen Sun, 孫翊仁
• Other Authors: Chien-Jung Lo
• Format: Others
• Language: en_US
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/dtm828

碩士 === 國立中央大學 === 物理學系 === 107 === Bacterial reproduction is a critical and dynamic life process. Here, we raise a simple yet fundamental question that how does the mother cell remodels the cell wall into two daughter cells? Compare to the DNA replication, we have far less understanding in the mechanism of cell wall remodeling due to the technical difficulties. In this thesis, we develop a new approach using membrane anchored protein as landmarks to study the cell wall synthesis dynamics. Bacterial flagellar motors (BFM) are membrane protein complexes anchored firmly on the cell wall. Thus BFMs position changes along with cell growth depend solely on the spatiotemporal coordinate of the cell wall insertion. By tracking fluorophore labeled BFMs in Escherichia coli while cell reproduce, we confirm the existence and determine the size of the cell wall growth inert zone. The normalized axial position of the motor remains constant while cell elongate, indicate a uniform axial cell wall insertion rate. During division, the mid-cell motors will be moved away from cell center indicating that the septum is completely formed by new cell wall material. With the understanding of the cell wall insertion, we built a modified Bernoulli-shift map to predict the position of the motors in each generation once it was formed. The smoothing property of the Bernoulli-shift map also indicate the motor distribution only determine by the newly born motor. With sequentially labeling motors with different color fluorophore, we are able to distinguish the newly born motors and confirm the concave distribution of the BFM is contributed by the preference of the motors to synthesize in the cell center. With this new experimental method, we open a new door to study the cell wall dynamics and membrane anchored proteins dynamics.