Arjan,
Klebsiella live on starch but other bacteria may live on other substances especially for us indigestible fiber can host a lot of bacteria. Cellulose is a good substrate for some bacteria it contains the same sugars as starch but they are only linked in another way (stronger) to each other. So if we eat enough vegetables there is enough to eat for the creatures. Sauerkraut is even better as it is already predigested by bacteria and only leaves fiber and nutrients and few energy.
Gerard
"Walk gently, breathe peacefully, laugh hysterically." -Nelson Mandela-
