|dc.description.abstract||The aim of this thesis is investigating the swarming dynamics of Vibrio alginolyticus from physical and biological aspects of self-propelled particles collective motions, colony expansion and cell division.
Vibrio alginolyticus is a marine bacterium with dual flagellar motor systems which are single Na+ driven polar flagellum and multiple H+ driven lateral flagella. When cells transfer from liquid to agar or high viscosity medium, the number of flagella on the cell surface increases, become highly motile on agar surface. The lateral flagella are expressed for swarm motility on the surface. To give a clear understanding of the functions of polar and lateral flagellar motors, three strains of Vibrio alginolyticus were used: 138-2 ( Pof + Laf + ), VIO5 ( Pof + Laf -), and YM19 ( Pof - Laf + ); wild type with single polar and many lateral filaments, polar only and lateral only, respectively.
During the swarm colony development, YM19 cells shows rich dynamical patterns such as turbulence, edge waving, edge streaming, jamming and mono-layer. In this thesis, I focus on the two collective patterns, edge waving and jamming.
1. Edge waving: The edge waving is happed when the cells are elongated and confined to the edge, a band of cells anchored on the non-moving contact-line show periodic waving. We calculate the velocity by particle image velocimetry (PIV) to study the mechanism of the waving patterns. The waving frequency is inverse proportional to the cell length. The mechanical origin of waving is the self-propelled motion of these cells with one end fixed on the edge of the colony.
2. Jamming: Jamming state is a very interesting phenomenon which can be found at inner region of colony with high density in single layer. Individual cells have high motility but all packed with other neighbors into a non-moving nematic patterns. We track the motion of single cell and calculate the MSD to study the jamming forming process. The jamming state formation is similar to the phase transition phenomenal.
3. The colony could expand rapidly at 1.03 μm/s. We found the local edge moving speed is correlated to the collective motion behind it. There is a high motility active region behind contact line. We propose a colony expanding model based on simple physical mechanism.
4. Cell division: Swarming cells suppress their cell division. Once the cells return to bulk liquid environment, the filamentous cells would return to Planktonic cell type quickly. We design a new agar plate system with bulk liquid environments to observe the dynamical process of cell division in vitro. We found the cells divide with correct size from one end sequentially and also other position of different size.