Nika Vafadari Week 6

Electronic Lab Notebook Week 6

Purpose

To hypothesize a model that shows the relationship between ammonium feed and another quantity, such as the production of carbon dioxide, within a yeast population in the process of fermentation.

Work Flow and Methods

• read the paper "Population Size Drives Industrial Saccharomyces cerevisiae Alcoholic Fermentation and Is under Genetic Control" by Albertin et. al
• took notes on the paper, comparing it to results from "The Concentration of Ammonia Regulates Nitrogen Metabolism in Saccharomyces cerevisiae" by ter Shure et. al
  • brief notes on paper

Results

Hypothesis

• Rate of nitrogen consumption governs Alcohol Fermentation (AF) time. Increased rate of nitrogen consumption (positively correlated with population size) decreases AF time, which is measured by observing when CO2 production rate drops below 0.5 g liter ^-1 h^-1, thus indicating the end of fermentation.
  • increased nitrogen consumption will cause CO2 production rate to reach Vmax sooner then crash
  • this is because nitrogen consumption positively correlated with K (carrying capacity)
  • increased population leads to increase in nitrogen consumption
  • population size governs AF time
  • increased population size leads to a decrease in glucose thus switching from fermentation to cellular respiration (end in fermentation)
  • fermentation= less yeast cells
  • cellular respiration=more yeast cells

Variables & Parameters

*State Variables:

• • y=concentration of yeast
  • c1= concentration of nitrogen
  • c2= concentration of glucose

*Parameters:

• • V1= rate of consumption of nitrogen
  • V2= rate of consumption of glucose
  • K= carrying capacity
  • Vmax= max rate of CO2 production
  • R= in place of relevant efficiency because two nutrients are required in this model

• • Note:
    • AF time=when CO2 production rate drops below 0.5 g liter ^-1 h^-1
    • N(t)=population size of yeast size at time t

Differential Equations

• 

Explanation

• when looking at a batch reactor instead of a chemostat, there is no inflow/ outflow rate of the nutrient

*Nitrogen:

• • c1(0)= initial concentration of nitrogen
  • V1=rate of consumption of nitrogen
  • y(c1/K1+c1 * c2/K2+c2)=amount of nutrient being consumed/ assimilated by the yeast

*Glucose:

• • c2(0)= initial concentration of glucose
  • V2=rate of consumption of glucose
  • y(c1/K1+c1 * c2/K2+c2)=amount of nutrient being consumed/ assimilated by the yeast

*Yeast:

• • yR(c1/K1+c1 * c2/K2+c2)= rate at which the nutrient taken up/consumed by yeast and converted into new yeast

*CO2:

• • Vmax=max rate of CO2 production
  • ( )=some variable that denotes how CO2 is affected by population size/ nitrogen consumption
  • x= concentration of CO2

Conclusion

• Using the results of the paper it was determined that nitrogen consumption and population size of yeast are correlated. In addition, a correlation between population size and Vmax, which is the max rate of CO2 production was established. Using this information a set of differential equations were created to model the effects of the rate nitrogen consumption and population size on CO2 production which determines the duration or time of alcohol fermentation, since the end of fermentation occurs when CO2 production rate drops below 0.5 g liter ^-1 h^-1.

Acknowledgments

• Key pieces from the paper, such as descriptions of variables measured, were copied and pasted into the brief notes on paper pdf.
• Spoke to Dr. Fitzpatrick in office hours on February 22, 2017 in order to determine what differential equations to use as a basis for mine.
• Except for what is noted above, this individual journal entry was completed by me and not copied from another source.
• Nika Vafadari 14:51, 22 February 2017 (EST):

References

• Albertin, W., Marullo, P., Aigle, M., Dillmann, C., de Vienne, D., Bely, M., & Sicard, D. (2011). Population Size Drives Industrial Saccharomyces cerevisiae Alcoholic Fermentation and Is under Genetic Control . Applied and Environmental Microbiology, 77(8), 2772–2784. http://doi.org/10.1128/AEM.02547-10
• Dahlquist, Kam D. (2017) BIOL398-05/S17:Week 6. Retrieved from http://www.openwetware.org/wiki/BIOL398-05/S17:Week_6 on 22 February 2017.

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