The selective constraint on gut bacteria is not merely to eat food, it is to facilitate the health of the gut. That is, a symbiote has different evolutionary go

The selective constraint on gut bacteria is not merely to eat food, it is to facilitate the health of the gut. That is, a symbiote has different evolutionary goals than a bug that is just out for a meal. Don't go looking in rotten food for this stuff; the most likely place to find it is in another person's gut.