There is no gain of information. It is just a matter of taking advantage of the information that is already there. And as Dr. Sanford points out in his book Genetic Entropy, when we do see actual beneficial mutations that change the total amount of available information, they invariably result from information loss, not information gain.
After the mutations. Bacteria could digest nylon.
Obviously that information was GAINED, even if you insist that the nylonase enzyme was simply ‘hidden’ within the esterase enzyme; it took MUTATION to UNLOCK that NEW INFORMATION.
As far as nylonase bacteria, the “total amount of available information” before the mutation didn't include the ability to digest nylon. The “total amount of available information” after the mutation included EVERYTHING the premutation bacteria could do, but with ADDITIONAL INFORMATION on how to digest nylon.
Obviously the total amount of information went up.