闡釋細菌線毛的伸長機制與評估其應用

Abstract

線毛是細菌外膜的附屬物，主要功能在協助細菌黏附宿主細胞並進而感染細胞。線毛的直徑約數個奈米、長度約1到2微米，結構類似螺旋彈簧。近年來，線毛經由奈米技術量測後，展現出線毛在受力伸長過程歷經三個階段。第一階段是遵守虎克彈簧定律。第二階段則是線毛持續伸長但拉力強度卻維持不變的特性，此已被Sticky Chain Model (SCM)的理論模型加以解釋。 在本研究中，我們建立兩種力學模型系統，用來作為類比的宏觀實驗進行模擬線毛在第一階段與第二階段的受力伸長機制，並且分別用來評估可否應用線毛彈簧特性製作一個線毛振盪式的病毒感測元件，以及形象化SCM的理論模型並推論其假設的正確性。 在評估線毛振盪式感測元件之可行性的實驗中，將市售彈簧串接一基座平台，總質量為427.43公克，用以模擬線毛在水中的阻尼振盪行為。藉由光學偵測系統追蹤振盪系統在砝碼放置前後的不同振盪軌跡，然後經由公式擬合後，得知自然共振角速率從37.86 狰 0.09 弧度/秒降為36.20 狰 0.29 弧度/秒，推測微砝碼的質量約為37.48公克。對照電子秤所秤得微砝碼的質量為38.54公克，其相對誤差僅為2.8%。 在形象化SCM的力學機制並驗證其假設的實驗中，SCM指出某一特定外力對粒子躍遷系統所作的功將符合原本雙捕捉陷阱的位能差，即Fd 责 岛xAB = VB – VA，而使得粒子在兩捕捉陷阱中的躍遷頻率可變成一致。為驗證此假設的正確性，我們調整兩雷射之光功率製造出兩捕捉陷阱的位能差為VB − VA = 1.03 kBT，且兩陷阱的間距為岛xAB = 430 奈米。模型預測水流外力應為Fd = 9.8 毕 10-15 牛頓，而實驗量測結果為8.4 毕 10-15 牛頓，兩者誤差僅為17.9%。 總體而言，第一部分的測試評估了線毛振盪式感測元件在under-damped條件下是可行的，且第二部分的實驗則已驗證了SCM的假設在外力作用下可達到某種程度的準確性。

Bacterial fimbriae, which are appendages expressed on bacteria, mainly assist bacteria in adhering to host cells and initiate bacterial infection. A fimbria is generally several nanometers in diameter and 1 to 2 micrometers in length displaying a helix-like spring. Recently, the mechanical properties of single fimbriae were characterized using some nanotechnologies and exhibit three phases in a force-elongation curve. The first stretching behavior of fimbriae agrees with the Hooke’s law. The second stretching behavior of fimbriae shows an unusual property, where a fimbria is stretched up to a few micrometers at a fixed force. The feature was described well by a sticky chain model (SCM). In this study, we built two mechanical model systems, which are regarded as analogical macro-experiments, to imitate the first two stretching mechanism of a fimbria, respectively. Furthermore, the first system was also used to assess whether fimbriae are suitable elements for a vibration-based virus sensing device. The second system was used to visualize the concept of SCM and examine the validity of an assumption in SCM. In the experiments on assessing the feasibility of a vibration-based sensor, we built a vibration system composed of commercially available springs linking a platform, whose total mass was 427.43 grams, to imitate the damped oscillation of a fimbria in water. By recording different vibrating trajectories of the platform with and without a loading weight measured using an optical tracking system and by analyzing the data with a curve fitting method, we observed the resonant angular speed of the vibration system decreasing from 37.86 □ 0.09 rad/s to 36.20 □ 0.29 rad/s and estimated the weight of 37.48 grams in mass. Finally, a relative error of 2.8% was derived from a comparison to the weight of 38.54 grams measured using electronic scales. In the experiments on visualizing SCM and examining the validity of SCM, SCM provided an assumption, where a specific external force Fd, which does a work on a particle dwelling in dual wells of different potential energy VB – VA, so that Fd □ □xAB = VB – VA, can change the transition rates of the particle in the wells to be identical. To examine this assumption, we controlled the laser power to create a potential energy difference VB − VA = 1.03 kBT between well B and well A. Furthermore, the controlled spacing between the potential wells was □xAB = 430 nm. Therefore, a predicted flow force was derived at Fd = 9.8 □ 10-15 N from the model. Finally, a relative error of 17.9% was derived from a comparison to the really controlled flow force of 8.4 □ 10-15 N. In summary, the first part of the study demonstrated that the fimbriae-based vibration sensor situated in an under-damped condition is available and the experiments in the second part have approved the assumption in SCM conditionally.