| 摘要: | 本篇論文主要探討溶藻弧菌的群游動態行為以及群體和單一長型細菌自我推動的運動。自我推動粒子在理論與實驗方面都已被研究，但理想的自我推動粒子系統受限實驗技術，目前理論計算仍領先實驗研究。細菌群游是一種相當良好的方法建立自我推動粒子系統。我們量測了溶藻弧菌的群游行為並建立一套自我推進粒子系統的實驗。
溶藻弧菌是一種擁有兩種鞭毛馬達系統的海洋類細菌，兩種鞭毛馬達分別是單一長在菌體極端由鈉離子驅動的鞭毛（極端鞭毛）和多條分佈在全身的氫離子驅動鞭毛（側邊鞭毛）。當細菌長在洋菜膠培養皿上，菌體會抑制分裂和延長體型，進入群游的型態。我們利用三種基因改良的溶藻弧菌：138-2(擁有兩種鞭毛)、VIO5(只有極端鞭毛)、YM19(只有側邊鞭毛)比較不同種鞭毛在膠狀洋菜膠與水溶液環境的運動。YM19在膠體表面表現活躍的群游動能性，可做為一個理想的細菌群游和自我推動粒子實驗系統。
在YM19菌落生長期間，細菌呈現非常多元的運動結構；例如渦流狀、邊界波浪、邊界湧流、塞擠和單層的狀態。我們使用粒子影像速度測量(PIV)的計算方法得到各流場速度和渦度，並藉由時間和空間的頻率次方頻譜描述各行為的特徵。不同的細菌濃度和邊界條件呈現不同的動態樣貌。當菌落邊界被限制前進，會有一帶狀區域銜接在被禁止移動的菌落邊線上做週期擺盪，其頻率約0.8赫茲。驅使的力不僅須由漩渦區提供，同時須要自我推動的細菌群形成波動。在菌落擴張的時候，菌落邊線並不是同步向前推進，而是由後面的細菌推擠。在不同區段突出與追平，菌落內部的運動性和集體運動是菌落擴張的關鍵因素。
利用高速攝影機和顯微鏡可以在菌落單層的區域追蹤單隻細菌。相對少量的長型細菌和周遭多數的短型菌體呈現高動態的形體結構。一般而言，細菌的細胞壁相當堅硬以維持菌體形狀，然而短型細菌維持像桿狀的同時，長型細菌被周遭短型細菌擠壓、碰撞卻可以大角度的彎曲。長型細菌的身體兩端呈現獨立的運動。長型細菌還可以自我有序聚的集，變成一個旋轉的螺旋圈。螺旋圈可由旋轉方向和中心結溝分成單層順時(CW) 、單層逆時鐘(CCW)、雙層順時(DCW)和雙層逆時鐘(DCCW)螺旋圈。螺旋圈的長度介32到296微米，旋轉速度2.22到22.96 rad/s。這些螺旋圈的轉速穩定，但整體位移會受短型細菌群的碰撞改變。螺旋圈的形成和拆解是由長型細菌的區域方向改變以及周圍細菌的碰撞造成。穩定旋轉的螺旋圈在主動驅動的系統證實在一不平衡的背景環境，區域性的穩定結構是可以存在的。螺旋圈自我有續聚集的過程或許是一個值得開發的微米技術。
The aims of this thesis are investigating the swarming dynamics of Vibrio alginolyticus and studying the collective motions and individual dynamics of self-propelled long bacteria. Self-propelled particle (SPP) has been studied both in theoretical and experimental approaches. However, theoretical works lead experimental works because of the limitation of manufacturing ideal experimental SPP systems. Bacterial swarm is a good candidate for building an experimental SPP system. Here, we survey the swarming behavior of Vibrio alginolyticus and build up swarming protocol to perform self-propelled particle experiments.
Vibrio alginolyticus is a marine bacterium with dual flagellar motor systems, a Na^+-driven polar flagellum and multiple H^+-driven lateral flagella. While growing on agar plate, they elongate without division into swarming phase. Three strains of Vibrio alginolyticus, 138-2 (wild-type), VIO5 (Pof^+), and YM19 (Laf^+) were first examined in both agar plate and aqueous environments. We found that YM19 strain shows very strong surface swarm motility and is an ideal experimental system for both bacterial swarming and self-propelled particle experiments.
During the swarm colony development, YM19 cells shows rich dynamical patterns such as turbulence, edge waving, edge streaming, jamming and mono-layer. We calculate the velocity fields by particle image velocimetry (PIV) and characterize the dynamics of the velocity by power spectra and vorticity calculation. The cells show different dynamical patterns and movement in different cell-densities and boundary conditions. With confined edge, a band of cells anchored on the non-moving contact-line show periodic waving about 0.8 Hz. The driving force is not only from the external turbulence region but also the self-propelled cells in the band. During the colony expansion, the contact-line is not marching together but protruding by a group of cells behind it. Both cell motility and collected motion are critical for the colony expansion.
At mono-layer, single cell can be tracked by microscope and high speed camera. In this region, some long cells are interacting with large amount of short cells and showing very dynamical configurations. The cell wall is rigid to maintain the bacterial shape. However, long cells can be bended by the collisions of short cells. Short cells are like a rigid rod while long cells are bendable and the two ends move independently. Long cells can be self-assembled into rotating spiral coils. Four types of spiral coils can be found featuring by rotational direction and the center structure: single clockwise (SCW), single counterclockwise (SCCW), double clockwise (DCW), and double counterclockwise spiral coil (DCCW) spiral coils. The length of spiral coils cells are between 32 to 296 μm. The rotational speeds are between 2.22 to 22.96 rad/s. These spiral coils rotate stably and the displacement are strongly influenced by the collision of short-cells clusters. The folding and unfolding of spiral coils are the results of the interaction between cells and the change of local moving direction of long cells. The finding of stable spiral coils in the active system indicating the existence of a local stable structure in the non-equilibrium background. The self-assembled process of spiral coil may inspire a new micro manufacturing technology. |
