CONFOUNDER. “The earlier potentiating mutations did not confer any immediate advantage with respect to using citrate, but they may have been beneficial with respect to growth on glucose. If so, it is possible that other populations in the LTEE have also become potentiated and might evolve the Cit+ phenotype, although no others have done so even after >50,000 generations.”
https://www.nature.com/articles/nrg3564