Nika Vafadari Week 7 Update

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Electronic Lab Notebook Week 7 Update

Purpose

To edit previous model generated in Week 7 in order to incorporate the relationship that exists between glucose consumption and CO2 production in hopes of creating a better representation of the relationship between nitrogen consumption, glucose consumption, the growth of yeast, and CO2 production rate during fermentation in yeast.

Work Flow and Methods

  • While the previous model aimed to determine if the rate of nitrogen consumption does in fact control alcohol fermentation time since Albertin et. al found that fermentation is controlled by yeast population size (found to have a positive correlation with nitrogen consumption rate), the rate of nitrogen consumption and glucose consumption had the same effects on the model when altered.
  • Therefore, in order to differentiate the effects of the rate of glucose consumption and nitrogen consumption on CO2 production rate, the relationship between glucose consumption and CO2 production has to be taken into account an incorporated within the equations
  • As Albertin et. al discusses, during the process of fermentation as glucose decreases, CO2 increases. However, once glucose levels are low, cell switches from fermentation to cellular respiration, which is indicated by the drop in CO2 production rate to below 0.5 g liter ^-1 h^-1.


  • To better represent the relationship between glucose consumption and CO2 production, V, which represents the amount of CO2 produced was incorporated into the rate of glucose consumption equation in order to indicate that the CO2 being produced comes from the glucose
  • Now V represents the amount of glucose being converted into CO2, as shown below in the updated differential equations
    • Updated Differential Equations
  • Since this is a batch model there is no steady state.
  • used equations to create function on matlab
  • Function:
  • updated function
  • created script for function in order to plot CO2 production rate vs. time
  • updated script

*state variables:

    • c1= concentration of nitrogen
    • c2= concentration of glucose
    • y= concentration of yeast
    • V= amount glucose converted to CO2

parameters:

    • V1= rate of nitrogen consumption
    • V2= rate of glucose consumption
    • K1= metabolic constant (1/2 Vmax of nitrogen)
    • K2= metabolic constant (1/2 Vmax of glucose)
    • R= replaces relative efficiency
    • Vmax= max rate of CO2 production


  • plotted function, changing the rate of nitrogen consumption and the rate of glucose consumption one at a time in order to analyze their effects when all other parameters remained constant

Results

  • First the effect of the rate of nitrogen consumption was observed at the values of V1= 10, 50, 100 with the other parameters set at V2= 10, V3= 4, K1= 2, K2= 2, R= 5 (as they were in the previous model)
  • Therefore, the same exact graphs were generated as seen in the presentation, showing that as the rate of nitrogen consumption increases, alcohol fermentation time decreases as shown by the crash of CO2 production rate below 0.5 g liter ^-1 h^-1


  • However the effect of the rate of glucose consumption was observed at the values of V2= 10, 50, 100 while the other parameters remained constant at the same values (V1= 10, V3= 4, K1= 2, K2= 2, R= 5) there was a significant change in the effect of the rate of glucose consumption on alcohol fermentation time
  • Instead of producing the same exact results as the change in the rate of nitrogen consumption, which is what occurred in the previous model, the changes in the rate of glucose consumption produced some very interesting results as shown below.
  • graph1
  • Fig. 1. The figure above displays the rate of CO2 production over time when V2=10, V1= 10, V3= 4, K1= 2, K2= 2, R= 5.
  • graph2
  • Fig. 2. The figure above displays the rate of CO2 production over time when V2=50, V1= 10, V3= 4, K1= 2, K2= 2, R= 5.
  • graph3
  • Fig. 3. The figure above displays the rate of CO2 production over time when V2=100, V1= 10, V3= 4, K1= 2, K2= 2, R= 5.



Conclusion

While alcohol fermentation time was hypothesized to be controlled by the rate of nitrogen consumption due to the findings of Albertin et. al, which determined that yeast population size controls fermentation, the figure above display that that rate of glucose consumption plays a role in the duration of fermentation as well. For example, as seen in Fig. 2. which greatly sticks out from the other two, the rate of CO2 production is seen to increase alcohol fermentation time when increased from V2=10 to V2=50. These findings indicate that the rate of nitrogen consumption (based on population size) may not be the only factor controlling alcohol fermentation time. However, the model still needs to be reevaluated in order to better display the relationship between nitrogen consumption and glucose consumption in order to better differentiate their effects which cold be down potentially using a chemostat model.

Acknowledgments

  • Except for what is noted above, this individual journal entry was completed by me and not copied from another source.

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 7. Retrieved from http://www.openwetware.org/wiki/BIOL398-05/S17:Week_7 on 22 March 2017.






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