HOW COME?: Spores can turn fruit into moldy oldies

How come foods like apples can get moldy, even in a cold refrigerator crisper drawer? asks reader Stephanie Waslin.

Ever start to bite into a red, ripe strawberry, only to discover a slimy white coating on the underside? As the fast food commercial goes, "You gotta eat." Except in this case, it's mold that's beaten you to a tasty fruit snack.

Mold and other kinds of fungus are champions at chowing down, and they're not picky eaters. In fact, human feet are favorites of fungi, who enjoy making a lunch of dead skin cells between your toes (spawning dozens of athlete's foot remedies).

What is mold, anyway? Fungus can't be categorized as a plant or animal. The Fungi - from mold to mushrooms - form their own kingdom. And the fungi kingdom is huge; scientists estimate there are more than 1 million species worldwide. The fungus is definitely among us, accounting for a startling one-quarter of the mass of all living things on Earth.

That's a good thing, since the fungi are among the best natural recyclers, reducing fallen trees and fruit to fertile soil. Unfortunately, fungi don't discriminate, and they're just as happy reducing an overripe peach hidden in your fridge to a rotting mass.

Microscopic mold spores are found nearly everywhere and grow quickly in warm, moist conditions. So a cold refrigerator will keep food mold-free longer. But some molds grow fine in chilly temperatures. And given enough time, mold always wins. Some ways to minimize mold: Keep the refrigerator clean, using baking soda and water to clean inside and a weak bleach solution on rubber door gaskets. And if food looks moldy - a bit of white fluff on one strawberry in a bunch or a soft spot on an orange - don't bring it home.

Molds may annoy us or even sicken us. No one wants to (or should) eat a moldy slice of bread. But molds are also our friends. Penicillium mold gives us both antibiotics and blue cheese dressing. Yeast makes bread dough rise as it consumes sugar and spits out carbon dioxide. And let's not forget mushrooms on pizza.

Molds come in a rainbow of colors and have a surprisingly complicated genetic code. When scientists mapped the genes of a reddish bread mold called Neurospora crassa, they discovered about 10,000 genes (we humans may have about 25,000). They already knew that the mold was exquisitely in tune with the passing of days on Earth, since it both eats and sends off spores in 24- hour shifts. But they also found genes that allow this mold to sense red light, even as it lurks silently in your breadbox.

And while this red mold likes bread in the warm indoors, it also thrives in the aftermath of forest and field fires, using the smoldering fire's heat to multiply, then happily living off the sugars in singed plants and trees.