The main aim of this thesis is to provide a precise method by which the growth of the yeast Saccharomyces cerevisiae can be standardized from a specified initial optical density (OD). To apply the proposed method of standardization and also to compare with the previous methods, we use two datasets: one consists of 99 wild-type yeast strains growth data, observed for 24 hours and the other consists of 200 wild-type yeast strains, observed for 44 hours, cultured in normal environment. We propose a method to standardize the growth of yeast with respect to an initial OD, fitting two observed growth curves at the same time by the modified Chapman-Richards growth model. We check the fitting and standardization of growth by residual plot and calculating the coefficient of determination. To verify the efficiency of the proposed method, we standardize growth curves at the
mean initial OD values for each dataset by the proposed method and also by the previous methods, and compare the estimates of the physiologically growth parameters: the lag phase, the maximum relative growth rate and stationary phase
OD increment. The method works well for close observed growth curves. It shows better result for lag phase using distant observed curves but slightly worse results for the
other two growth parameters. Weighing the observations has a better effect in this case and it is found to be insensitive with respect to the point of standardization. Finally, a generalization of the method is also discussed. |