Let's say you want to create a strain of bacteria that is resistant to heat. You expose all bacteria to high heat and those who have mutated to survive this heat will be the survivors. Then you allow this group to reproduce and continue to gradually raise the heat until you are left with a population of highly heat-resistant bacteria.

Let's say you wanted to do the same but instead of selecting heat resistance you want to select for the production of a certain enzyme, for example amylase. How do you manipulate the environment so that only those with higher production would survive?

One thing that comes to my mind would be introducing all the microbes to an environment where the substrate they need to break down to survive is scarce. So the specimens that would create the most enzymes to break it down would survive. But then all of the other specimens would benefit too because the enzyme from the high-producing specimen would also give them the substrate they need to survive - so it would not be isolated but rather would 'carry the entire population on its back' (I have no idea whether this is how it would work, this is an idea)

  • $\begingroup$ Interesting, has there been a case where the enzymes did change shape to adapt? Also, wouldn't the poor enzyme producers also use up the product of the enzymatic reaction and therefore the high-producers won't be isolated? $\endgroup$
    – Anonymir
    Jun 13 at 9:18
  • $\begingroup$ No. Most substrates for growth have to be taken up by the cell before being metabolized. The lac operon mentioned by @user338907 contains a permease gene for this purpose. $\endgroup$
    – David
    Jun 13 at 18:23
  • $\begingroup$ @user338997 ? Lac permease doesn’t transport lactose into the cell? $\endgroup$
    – David
    Jun 13 at 18:39
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    $\begingroup$ I suggest you do a little reading on this yourself. Some substrates like proteins or polysaccharides are too large to be taken up by cells so they do excrete extracellular proteases and glycosidases to break them down into smaller molecules that can be taken up and metabolized internally. Ok, starch will not be permeable, but I was considering the general situation. If you need a group of enzymes to metabolize starch, other bacteria can only hitch a ride on the extracellular ones, which is no use if they lack the intracellular ones. $\endgroup$
    – David
    Jun 13 at 19:19
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    $\begingroup$ But if we take glucose for example, isn't glucose the final form of sugar needed for cellular respiration? And if there is a secretion of enzymes to the extracellular environment, and the activity of these enzymes results in free glucose in the extracellular fluid environment, then it seems these bacteria could soak it up and hitch a ride., preventing natural selection (they weren't the fittest but they were always around the fittest) $\endgroup$
    – Anonymir
    Jun 14 at 9:46

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