dc.description.abstract | Through the observation of the movement of Vibrio alginolyticus variant strain YM19 (Laf+, Pof-) on agar surfaces, we investigated the dynamics of micrometer-sized active rods. Based on Joule expansion (passive expansion), we categorized the bacterial behavior into a two-stage model. In the first stage, when the bacteria enter the "cavity," they gather at the channel opening and slowly expand towards the center, while a small fraction of bacteria rapidly moves along the inner edge of the cavity. The second stage involves three different diffusion modes and a phenomenon contrary to the coffee ring effect, resulting in distinct precipitation patterns.
Furthermore, we examined bacterial movement on different terrain by creating agar surfaces with varying heights, including "cliffs" (representing changes in agar surface height from high to low) and "micro-pillars." We observed that bacteria avoid falling off cliffs and instead move parallel to the cliff edges. However, due to bacterial aggregation and pushing, occasional incidents of bacterial falling off cliffs occur. In such cases, bacteria move along the cliff walls. When bacteria encounter micro-pillars, we observed that they move parallel to the edges, forming "channels." As bacteria increase and aggregate, these channels expand continuously. Additionally, we noticed bacterial gathering and accumulation in various directions within the channels. As the channel edges expand, bacteria move to the next pillar and repeat the same movement pattern until the entire system is filled.
Based on these two studies, our findings demonstrate the complex and intriguing dynamic behavior of micron-sized active particles (bacteria) on agar surfaces. We observed different modes of expansion during bacterial spreading, leading to distinct patterns. Moreover, when encountering terrain obstacles, bacteria exhibited avoidance of falling off cliffs and moving along the edges, as well as the formation of channels and expansion on micro agar pillars, suggesting strategic behavior during their movement. These insights enhance our understanding of the behavior of micron-sized active particles. | en_US |