Team:Wageningen UR/testpage

Wageningen UR iGEM 2016

 

Metabolic Modeling

In order to assess the real world viability of the BeeT we evaluated the proposed system of application by making a model of the entire system. To do this we used Flux Balance Analysis (FBA) to make model the base chassis. The chassisThe chassis is the base organism that is modified of BeeT is a variant of ​ Escherichia coli, for which it is known that it does not grow in sugar water, mainly due to high osmotic pressure. 1 The question remained: Does it survive there, and if so, for how long?

What is Flux Balanace Analysis

Flux balance analysis (FBA) is a mathematical method for simulating metabolism in genome-scale reconstructions of metabolic networks.


Key Results

The relationship between max ATP available for survival and water efflux is shown in Figure 1, it demonstrates that there is a linear relation. This implies that if no water is available for ATP used for maintenance outside cell growth, the cell will die. When the model is run without any modification, ie in an environment where it is in the exponential growth phase an ATP Maintenance flux of 3.15 mmol*gram Dry Weight^-1*hour^-1 is given as output by the model.

We do not know the amount needed in sugar water conditions, but because of these results we can start looking at the relationship between survival time and water efflux.

In Figure 2 we can see not only the relationship of survival time against max ATP available for survival, but also how different thresholds of minimal cell-water tolerance would affect this relationship. The minimal cell-water tolerance threshold gives the value at which percentage of the remaining cell-water the point of no return for the cell had been reached. Which has a drastic effect on survival time, changing 20 minutes of maximum survival time to a mere ~90 seconds in the worst case scenario.

Conclusion

Figure 1 shows us that osmotic pressure alone can indeed have an effect on cell regulation and cell death and from Figure 2 it appears that the minimal water allowance threshold has a high impact on range of possible times. We also must accept that the range outside of 90 seconds to 90 minutes is completely undocumented territory as we can only say something about non-infinite values. Because we don't exactly know how much mmol*gDW-1*hour-1 is needed for proper maintenance under harsh conditions, we can not say anything about where on the scale that would be.

What we can say is that if the cells can survive for longer outside of this period, then they must have enough ATP available for basic maintenance, and that if cell death occurs then, that other processes than pure water-efflux must be the cause of that. Perhaps combinations of lack of nutrients and water-efflux, or over production of osmolytes to keep the balance.

References

    1. Cheng, Y. L., Hwang, J., & Liu, L. (2011). The Effect of Sucrose-induced Osmotic Stress on the Intracellular Level of cAMP in Escherichia coli using Lac Operon as an Indicator. Journal of Experimental Microbiology and Immunology (JEMI) Vol, 15, 15-21.