Active fluids are often is known as the aqueous suspensions of self-propelled elements such as bacteria, algae, or sperm cells, which their properties fundamentally differ from conventional fluids. Active fluids exhibit remarkable physical manifestations over a wide range of scales, from time-dependent microscopic diffusion to the large-scale colonization of aqueous spaces. Properties of active fluids depend on the behavior of microbial suspensions, among which motility plays a crucial role.
In this work, we focus on the effect of microbial growth and aging on microorganism motility. Hence, the motility behavior of cyanobacterium Synechocystis sp. CPCC 534, and its relationship with aging were investigated in a closed microfluidic chip. The growth of Synechocystis cultures was followed from the lag phase, through exponential and linear growth up to the stationary phase. Culture samples were periodically examined; cell populations were measured by spectroscopy technique and cell trajectories were tracked by video-microscopy. Cell trajectory length and average cell motility were extracted from the video recordings and were correlated with the age and growth phase of the bacterium.