Warthaug
Contributor
The above was concerning my comment that if the mutants were placed back in natural environments they would get outcompeted.
https://www.msu.edu/~lenski/
click on: publications-complete list-acrobat file (for #180, the PNAS paper)
First full paragraph on page 7904
This stable coexistence suggests that the Cit- cells are superior
to the Cit+ cells in competition for glucose, allowing the former
to persist as glucose specialists. Indeed, the Cit- cells have a
shorter lag phase and higher growth rate on glucose than do the
Cit+ cells (Fig. 2).
However, you're ignoring a rather simple part of evolutionary theory - species evolve to survive in their current environment. There is no drive to maintain fitness for past environments; indeed, such a drive could be quite detrimental. I already used this example, but by your logic we humans are less fit than fish, as we are not as fit in our old (aqueous) environment, as we have lost our gills.
That of course is nonsence; we're superbly adapted to our current environment, and have lost the adaptations we needed when we were lobe-finned fish. By yoiur logic, evolution would only be true if we kept the fins & gills. The same it true of these bacteria - there is little glucose in their environment, compared to their previous environment (which also wasn't natural, but rather a lab, btw), and as such their ability to better use citrate is a vast improvement.
And, as I pointed out in a previous post, depending on which "natural" environment you're talking about, the ability to utilize citrate, even if that comes with poorer glucose metabolism, may still represent an advantage. In the human gut, or inside of human cells, for example - in both of those environments, free citrate is more available than glucose. Which is why many infective e. coli pick up oxic citrate metabolism genes from other species.
Bryan