Thanks for your replies. What I need to prove is that the E. coli, a known facultative anaerobe, is definitely growing aerobically, ie expressing only aerobic proteins and no anaerobic ones (which would invalidate my work so far). It's quite easy for a flask culture to become anaerobic if its too full or too old, and of course you can't tell by looking.
So the test needs to be done on the actual culture itself - subculture to any other medium would only prove what the bacterium is actually capable of, not what it's doing at the present.
So, any ideas? Keep 'em coming!