Characterisation and modelisation of phenotypic variability in saccharomyces cerevisiae: the interaction of nutrient stress, cell size and morphology

Abstract

In this work, the size (volume) and morphological characteristics of the yeast Saccharomyces cerevisiae CEN.PK 113-7D CHI-GFP were characterized and modeled under nutrient stress. The goal was to determine if these aspects were critical factors in explaining phenotypic variations. The distribution of cell volume was analyzed using flow cytometry (via Forward Scatter Area) on the dataset from Tieke, which consisted of a continuous culture with varying dilution rates, either accelerating or decelerating. The data suggests that the cell size distribution followed a skewed log-normal distribution, with the parameters of this distribution being influenced by nutrient availability. Under respiratory metabolism, a decrease in the mean cell size in conjunction with nutrient availability was observed. However, after the transition from a respiratory to a respiro-fermentative metabolism due to the Crabtree effect, an increase in the mean cell size with nutrient availability was noted. Furthermore, a comparison of cell size using flow cytometry and microscopy at different dilution rates not only confirmed previous observations about cell size but also allowed the budding state of cells to be observed. It was shown that under favorable nutrient conditions, smaller cells have an increased likelihood of entering the budding phase. A method was then proposed to distinguish the distributions of budding and unbudding cells in flow cytometry based on observation in microscopy. These features were integrated into a pre-existing modeling tool, FlowStoCKS (Flow cytometry Stochastic Kinetic Simulator), to assess whether the model was enhanced by the addition of these characteristics. The results indicated that size and budding state were indeed key determinants of phenotypic variability.