BASICS
NATALIE ANGIER


In the eastern United States, thousands of cave-dwelling bats have died of an aggressive fungal disease called white-nose syndrome, and hundreds of thousands if not millions more are at risk of contracting the condition. Frogs and salamanders worldwide are dying in catastrophic numbers, very likely of a fungal disorder called chytridiomycosis, which clogs an amphibian’s skin and deranges its blood chemistry. Forests along the western and southern coasts of North America are withering as a result of fungal blooms injected into the wood by pine-boring beetles.

Can’t we just break out a few giant bottles of cleaner and wipe the world clean of its infernal fungus, its allergenic mold and sporulating mildew, its rot and blight, smut and rust?

We can never rid the world of its fungus, of course, nor would we want to. Some 100,000 species of fungi have been tallied, and scientists estimate that at least another 1.5 million remain to be discovered.

Fungi are everywhere, on every continent and in every sea, floating in the air, lacing through the soil, resting on your skin, colonizing mucosal cavities within, and settling on long-neglected pieces of fruit. And though some fungi are pathogenic and will kill the living tissue they have penetrated, the vast majority are benign, and many are essential to the life forms around them.

“They are the major decomposers,” outdoing even bacteria, worms and maggots, said David J.McLaughlin, a mycologist at the University of Minnesota.

Fungi also have a talent for symbiosis, for establishing cross-kingdom relationships that keep the fungus fed and happy while lending its partner vast new powers. Maybe 90 percent of all land plants depend on the so-called mycorrhizal fungi that stipple their roots and feed modestly on their plant sugars to in turn supply them with nutrients from the soil like phosphorus and nitrogen.

Fungus may well have given rise to human culture. For a loaf of bread to share with old friends and a jug of wine to help forge new ones, we can thank the fungus Saccharomyces, baker’s and brewer’s yeast.

More recently, Saccharomyces has served as an agreeable model organism in the laboratory, an excellent way to explore how genes behave and cells divide and a much cheaper experimental subject than a rodent. Fungal cells turn out to be surprisingly similar to animal cells, and researchers recently determined that the fungal and animal lineages didn’t split from each other until millions of years after both had branched away from the plants.

The most familiar fungi are the mushrooms. Given sufficient food and room, the filaments of a founding fungus may grow over thousands of hectares of soil and persist for centuries or millennia, all the while spawning genetically identical mushrooms above ground, and biologists think that such hyphal masses are some of the largest and most ancient organisms on Earth.

Most fungi are adapted to grow in cool temperatures, which is why the pathogens among them tend to prey on plants, or cold-blooded animals like insects, reptiles or amphibians.

Even then, most fungal diseases are not fatal, and the virulent strain that is thought to be involved in today’s mass amphibian die-offs may have been introduced into natural populations by frogs used in medical research.