Evolution You engineer yeast to produce biofuel from complex carbon. Your metabo

Question

Evolution

You engineer yeast to produce biofuel from complex carbon. Your metabolic engineering causes the yeast to excrete a costly extracellular protein that breaks the cellulose down into sugars the yeast can take up and eat. You are excited to make your first million and start growing the yeast in giant bioreactors. The bioreactors keep the yeast suspended in well-mixed liquid which contains the complex carbon. The yeast breakdown the carbon, feed on the released sugar and continue to divide as they produce biofuels. The bioreactors work great for a week, but then the yeast population stops breaking down the cellulose and starves.

A)   Provide an explanation based on social evolution to explain the crash.

B)   What is one way you might be able to alter the selection to avoid this outcome?

C)   Why might changing an ultimate driver of the population crash be a better solution than changing a proximate cause of the crash?

PART C ESPECIALLY NEED HELP

Explanation / Answer

A. The possible reason that the crash occurs is that the yeast population has reached the stationary phase.

It adapted to the substrate during the lag phase, grew and metabolised rapidly during the log phase but the growth stalled in the stationary phase and since no action was taken during this phase, the yeast cells started dying since it stop breaking down the complex carbon (death phase). The possible reasons for the yeast population crash and no metabolism can be the following -

All the above factors may have worked together as well.

B. To counter the problem the following solutions can be employed -

C. Because changing a proximate cause of the crash would be a temporary solution to the problem, the crash would still happen but after a prolonged time. Its not a permanent solution. For example, if we assume that the yeast stops growing and breaking down cellulose because the presence of large concentration of biofuels has changed the pH of the media , adding a pH buffer to the media might be a good solution temporarily, and it would give us time to run the bioreactor for sometime more. But even pH buffers have limits and soon a pH crash would occur in the future. Now if we change the ultimate driver of the population crash, i.e. the high concentration of biofuels in the media by extracting it and adding fresh media instead, the yeast would resume cellulose metabolism, we would get our biofuel and also save the costs on not just a failed bioreactor but also on purchasing unnecessary buffer besides making our first million.

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