Cellular decision-making models in yeast

Decision-making is ubiquitous throughout all levels of biological complexity, from social insect colonies to individual cells and multi-cellular organisms. The study of decision-making by different fields has suggested that there are shared underlying principles and decision-making mechanisms that can be used to describe the behaviour of any given biological system, regardless of its specific nature. The relatively recent application of decision theory to the study of cellular systems has provided great insights into the nature of different cellular processes. In this thesis, I aim to explore and describe the sugar consumption dynamics observed in a yeast culture growing in a binary-sugar mixture. In order to study this cellular process, I develop several mathematical models to describe the sugar consumption behaviour of yeast. The models are influenced by the work of Pais et al. (2013) on house-hunting honeybee swarms. I use experimental data gathered from yeast cultures grown in maltose, galactose, and a mixture of both sugars to validate and parameterise the models. I show that with a single parameterisation, the models are capable of replicating the metabolic and biomass experimental data of yeast growing in single sugar, as well as binary-sugar mixtures. Additionally, the models are studied by means of bifurcation and dynamical systems analysis. As pointed out by Aidelberg et al. (2014), microorganisms growing in a media with two different sugars present one of three different consumption strategies: 1) simultaneous consumption of both sugars present in the media, 2) exclusive consumption of one of the two sugars available, and 3) no consumption. I show that the models developed present features such as decision-deadlock, deadlock-breaking bifurcations, and deadlock-restoring bifurcations, which give rise to these consumption strategies. We also show that the transition between these regimes depends on the value of key parameters of our models.