The life of diatoms is governed by two coupled cycles on different time scales: the cell cycle and the intergenerational size reduction and restitution cycle. The cell cycle influences the progression of the intergenerational cycle and a population’s size distribution. Previous studies have indicated that differences in division speed or intermitotic time may exist between cells resulting from the same division (siblings), and that these differences depend on each cell’s size. The existence of systematic asymmetries in the lineages of the benthic, motile diatom Seminavis robusta have been investigated using time-lapse recordings from a customized microscope. For data analysis, a Python program was written and subsequently evaluated. The program consists of a detector applying a weighted U-Net and a Kalman filter based tracking algorithm. To visualize and check the output of the algorithm, a user interface is provided as well. The program extracts information of cell lineages and tracks the inheritance of thecae and their relative size from the third recorded generation. The conducted experiments revealed no systematic asymmetry of cell cycle durations between siblings. However, the observed lineages exhibited entrainment of cell cycle duration which indicates a “kicked” cell cycle that has been reported for diverse other microorganisms before. The cycle duration oscillated with circadian time at the division and cells in one generation exhibited similar cycle durations while being dissimilar to the previous or next generations. Cells also predominantly divided in the morning. Besides cycle duration the motility of cells was investigated. Here, a significant difference between two siblings was found. The cells inheriting the smaller theca moved for longer periods and at higher velocities than the ones inheriting the larger theca. The latter often remained at the location of the division. Furthermore, the movement was tightly bound to divisions and rarely observed at later stages of a cells life. In summary, Seminavis robusta exhibits the characteristics of a kicked cell cycle which provides a starting point for deeper investigations into the underlying mechanisms and for an advanced understanding of the coupling between the cell and intergenerational cycle. Additionally, asymmetrical motility between siblings was discovered which might provide an advantage for sexual reproduction or in niche occupation and subsequently influences the population and its cycles.
Jonas Michel Ziebarth (Wed,) studied this question.