rbishop is right we are way :OT:.While this is all very interesting, I would like to remind all that the OP's question, dated 12/15/06 concerned an issue that is not being discussed and it involved a 72 hour period that has long ago expired. They also have not participated in the thread since then.
So it looks like we should be answering the question of how long the bacteria live without a food source. And some one might want to start a thread on the different effects of nitrifying bacteria. Thanks.
Everyone please continue this debate in the thread below:
http://www.aquariacentral.com/forums/showthread.php?t=94612