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Determining Yeast Respiration Rate in Glucose and their Cell Viability Claire McIntire BIOL 1050 Section 40 ABSTRACT The purpose of this study was to determine if the Saccharomyces cerevisiae cells grown with a 2% of glucose have a higher respiration rate than the cells grown in 0.5% of glucose. We also wanted to know which glucose concentration had a higher rate of viable cells. We used Trehalose as our glucose because it is easily found in yeast. We tested the cells respiration rate and viability levels. Our hypothesis stated that the respiration rate would be higher in the 0.5% concentration than the 2% concentration. Our second hypothesis said that the cell viability rate would be higher in the 0.5% than the 2%. We found that the respiration rate was not significant however, the viability rate was significant. INTRODUCTION Understanding the mechanism of glucose repression in yeast has proved to be a difficult and challenging problem (Trumbly et al, 2006). This is because yeast can ferment very well and does not always need cellular respiration. S. cerevisiae exhibits the Kluyver effect for trehalose: this disaccharide is assimilated and respired, but, in contrast to glucose or maltose, it cannot be fermented (Malluta et al, 2000). Fermentation is only used when oxygen is not available, however a yeast cell would be much more effective using cellular respiration, therefore trehalose is much more effective. The yeast used, S. Cerevisiae is well adapted to life in a range of chemical and nutritional conditions (Brauer et al, 2005). Glucose is the preferred use of energy

for yeast cells. Trehalose plays a roll in protecting cells, especially membranes from oxidative injuries (Herderio et al, 2006). In their study, they found that Trehalose protected the S. Cerevisiae from harm, therefore showing that its relationship must be positive. Trehalose was evidently a more effective compatible solute, per mole, than glycerol. (Mackenzie et al, 1988). Not only is trehalose a good source of energy for the yeast, but it is also better than glycerol, which is a vital supplement for most animals. METHODS AND MATERIALS First we extracted and obtained two yeast mediums of 2% Trehalose concentration and 0.5%. The following steps were carried out for both concentrations. We then set our spectrophotometer to 650nm and blanked it. After, we placed 0.9mL of yeast suspension and 100µL of methylene blue solution in a cuvette. Using the spectrophotometer, we recorded the %T every minute for ten minutes. We obtained 0.1mL for both concentrations of yeast and added the methylene blue solution, letting the cells stain for one minute. After, we placed them onto a hemocytometer, allowed cells to settle, placed onto a microscope at 400x magnification. Finally, we recorded the amount of viable, and nonviable cells along with the total number of cells per mL. RESULTS The average respiration rate when comparing both Trehalose concentrations is much higher in a 0.5% concentration than a 2% concentration (See Table 1). According to our P-Value proved that although quite different, the respiration rate is not significant. Similarly, when looking at the percentage of viability of cells, the 0.5% concentration is greater than the 2% concentrations. According to our P-Value in this instance, the difference was proved significantly different.

DISCUSSION Our hypothesis stated that there would be a significant change between concentrations for both respiration rates and cell viability. With our inferences and findings, we can say that the data did not support our experiment in the sense of significance for our cellular respiration rates, however they were supported in our cell viability. Development of resistance was accompanied by accumulation of trehalose and was apparently unrelated to glycerol content which, under these conditions, was always low (Mackenzie et al, 1988). Our findings also agree with this study because it also explains that trehalose is a very good source of energy for S. Cerevisiae. Trehalose markedly increased viability upon exposure to menadione stress (Herderio et al, 2006). This study was done to see how a certain glucose (trehalose) would protect a set of cells (S. Cerevisiae). This study also agreed with our second hypothesis about trehalose helping maintain the viability of the cells. CONCLUSION In this study, we saw marginal differences in respiration rates, however not significant enough to support our hypothesis. We also saw considerable differences in cell viability and was significant enough to support our hypothesis. Through further research we also saw that trehalose has been identified as one of the best sources of energy for the yeast S. Cerevisiae. Some weaknesses of this study could have been the temperature at which the yeast was stored, some research suggested differences in viability at different temperatures. Other weaknesses include human error, such as counting and calculating the amount of viable cells, or inaccurate measurements.

Future studies could try to confirm which type of glucose is the best for the yeast, or to confirm if trehalose also performs the same tasks in other type of yeast.

LITERATURE CITED Brauer, Matthew J., et al. “Homeostatic Adjustment and Metabolic Remodeling in GlucoseLimited Yeast Cultures.” Molecular Biology of the Cell, 9 Mar. 2005, https:// www.molbiolcell.org/doi/full/10.1091/mbc.e04-11-0968. Herdeiro, R.S., et al. “Trehalose Protects Saccharomyces Cerevisiae from Lipid Peroxidation during Oxidative Stress.” Biochimica Et Biophysica Acta (BBA) - General Subjects, Elsevier, 10 Feb. 2006, https://www.sciencedirect.com/science/article/pii/ S0304416506000134. Mackenzie, Kylie F., et al. “Water Stress Plating Hypersensitivity of Yeasts: Protective Role of Trehalose in Saccharomyces Cerevisiae.” Microbiology, Microbiology Society, 1 June 1988, https://www.microbiologyresearch.org/content/journal/micro/ 10.1099/00221287-134-6-1661?crawler=true. Malluta, É F., et al. “The Kluyver Effect for Trehalose in Saccharomyces Cerevisiae.” Wiley Online Library, John Wiley & Sons, Ltd, 10 July 2000, https://onlinelibrary.wiley.com/ doi/abs/10.1002/1521-4028(200007)40:3%3C199::AID-JOBM199%3E3.0.CO;2-E. Trumbly, R. J. “Glucose Repression in the Yeast Saccharomyces Cerevisiae.” Wiley Online Library, John Wiley & Sons, Ltd, 27 Oct. 2006, https://onlinelibrary.wiley.com/doi/abs/ 10.1111/j.1365-2958.1992.tb00832.x.

Table 1. Respirations rates and cell viability compared with both trehalose concentrations...