In lab tests or in the wild, has any yeast/bacteria/etc. evolved to be able to digest artificial sweeteners? Is this a theoretical possibility?
Given that aspartame is composed of two common amino acids I’d have to say yes. Lots of critters, in fact, can digest aspartame including yourself. (It takes so little to produce a sensation of sweetness it can be considered “no calorie” in the amounts used. It actually has 4 calories per gram).
Given the wide range of things various life forms have evolved to eat (including certain minerals/rocks and concrete) if something doesn’t already find some sort of nutrition or energy in the more synthetic sweetener something probably* could* evolve to do so.