Observation of the Transition Phenomenon of High-Density Cell Distribution in a Two-Dimensional Microspace of the Unicellular Green Alga Chlamydomonas reinhardtii

Understanding the spatial distribution (SD) of unicellular organisms is crucial for comprehending population dynamics and adaptive strategies at the microbial scale. These behaviors include the formation of ordered structures through intercellular interactions and the broader implications for ecosystem interactions. In this study, the spatial distribution of the motile unicellular alga Chlamydomonas reinhardtii was investigated, with a focus on high-density conditions approximated by an area fraction of phi = 10%. Cell counting was carried out by image analysis, which applies the quasi-two-dimensional observation technique developed in our previous studies to analyze cell interactions in microspaces with thicknesses of 80 mu m and 200 mu m using both variance-to-mean ratio (VMR) and Eberhardt statistics (ES). The study reveals that experimental results, when evaluated using both VMR and ES, confirmed a similar trend and a density-dependent transition in cellular interaction. This transition ranges from swarming at lower densities to dispersal at higher densities, with a critical boundary observed at approximately phi = 8%. The findings suggest that cell behavior in dense populations shifts due to limited space and resources, offering a new perspective on the adaptive strategies of cells. These insights could enhance understanding of the mechanisms governing cell behavior in crowded environments.