Colloquially we say that the sour smell of damp clothes (e.g. clothes that have been left in the washing machine for too long) is due to "mildew". But from what I can find (Wikipedia), "mildew" refers to several species which seem rather different, including some which only grow on plants.
Which species is the one causing my clothes to smell bad? I am in the Northeast U.S. — does the answer depend on that? Is there a region of the world without this species of fungus where my damp clothes would not smell bad?