How does lactic acid bacteria prevent bread spoilage caused by species of Bacillus bacteria?

Answer 1

http://www.nyx.net/~dgreenw/howdolacticbacteriaaffects.html

Answer 2

Sourdough bread is thought to be one of the oldest foods of humanity. A culture of yeast and lactic acid bacteria, when kneaded into bread dough, produces bubbles that make the bread "rise" and give a delicate texture. The shelf-life is extended because when bread spoils it is usually from mold. The lactic acid produced by bacteria makes the bread more acid "hence the sour taste" and this makes mold grow more slowly.