| dc.description.abstract | Bacterial swarming motility is a rapid and collective translocation of a bacterial population on the semi-solid surface by rotating their flagellar motors to generate thrusting force. In the last decades, people have demonstrated that there are many fascinating collective behaviors and pattern formations in the swarming colony of bacterial cells. In multiple layer region of swarming colony, turbulence state, edge waving, and edge streaming were observed in the swarm of Vibrio alginolyticus. People can only studied the collective behavior of bacterial cells due to the technical difficulty of individual cell tracking of high density region. However, the capability of single cell tracking can provide further insight to the collective behavior of the complex bacterial swarm. It is clear to see that cell alignment due to the excluded volume effect in the single layer region. Therefore, the swarming bacterial cells in single layer region is an ideal experimental system to study both bacterial properties and dynamics in active system.
People have studied the properties and collective behaviors of swarming bacterial cells for many years, but there are still many questions left unsolved especially in high cell density system. For example, how does the bacterial cells expand the colony, how does bacterial cells with peritrichous flagella form flagella bundle and generate propulsion. In this work, we studied the mechanism behind colony expansion with the use of confocal microscope, and demonstrate both the properties and collective behaviors of self-propelled particles in two dimensional systems by observing the swarming motion of Vibrio alginolyticus in single layer region.
By tracking the motion of each bacterial cell in single layer region of the swarm. We demonstrated the collective behaviors of swarming Vibrio alginolyticus with different cell density. Giant number fluctuation was observed in the system when the cell density is in the range of 0.2 to 0.6. At high cell density, bacterial cells were able to form a local order nematic structure, and the order is enhanced when both the average cell length and cell density increased. Two interesting properties of swarming Vibrio alginolyticus were observed in the system. First, some of the swarming bacterial cells were able to reverse their velocity direction with a frequency 0.7 hertz in three different densities. The mechanism of these velocity reversal events are different from the known mechanism of velocity reversal event in E. coli swarm. Second, some bacterial cells are able to travel long distance in high cell density system. Here, long range displacement events are considered as a result of wide distribution in force generation of cells. But the mechanism behind the velocity reverse events are not clear.
We also show that during the expansion, the motion of bacterial cells could change the local surface curvature of the colony, and make the surface tension a variable during the expansion. | en_US |