Co-opting and elaboration of existing systems is evolution.<quoted text>
E coli have a whole suite ---an operon---to confer citrate fermenting ability. They already possess the ability to "digest" citrate, but only under certain circumstances.
We have been through this before....
Short attention span?
Too close to bedtime?
Lenski himself stated, " A more likely possibility, in our view, is that an existing transporter has been co-opted for citrate transport under high oxic conditions"
Also see, in regards to the transporter:
Pos, K M, Dimroth, P and Bott, M, "The Escherichia coli Citrate Carrier CitT: a member of a novel eubacterial transporter family related to the 2-oxoglutarate/Malate translocator from Spinach chloroplasts, J Bacteriol 180(16):4160-4165, 1998. www.pubmedcentral.nih.gov/articlerender.fcgi...
This transporter is only activated under oxygen free conditions with good reason.
But you will never know the reason.....
The ability to digest citrate required a modification of existing systems and occurred through two separate mutations occurring thousands of generations apart, the first being apparently neutral until the second occurred.