From killers to dinner friends

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.

Fungi represent a kingdom unto themselves, up there in taxonomic sovereignty with the kingdoms Animalia and Plantae, the bacteria and the protists. 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, colonising mucosal cavities within, and festively decorating that long-neglected peach. 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 in their saprophagic industry, said David J McLaughlin, a mycologist at the University of Minnesota.

Fungi-plant symbiosis

Fungi also have a talent for symbiosis, for establishing cross-kingdom quid pro quos that keep the fungus fed and happy while lending its partner vast new powers. Maybe 90 per cent 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.
And botanists suspect that plants might never have made the leap onto land some 500 million years ago without their mycorrhizal assistants.

The fungus, 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 date 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 some nine million years after both had branched away from the plants.

The defining traits of a fungus are gustatory and architectural.

Whereas animals ingest a meal first and then digest it internally, fungi do the reverse.
After latching on to a suitable food source, they release enzymes to break down the substance into a soupy mash of sugars and amino acids, which they can then absorb through the membranes of their filamentous hyphae.

Some fungi remain simple, even unicellular, but others can sprout elaborate fruiting bodies packed with billions of microscopic spores, billions of wistful homuncular fungi.

The most familiar fruiting bodies are the mushrooms, with their vivid pigments of inscrutable purpose and their still more inscrutable forms, here a swollen pink pincushion or a bird’s nest filled with eggs, there a protruding black tongue or a batch of bright butter coral.

Given sufficient food and room, the filaments of a founding fungus may grow over thousands of acres of soil and persist for centuries or millennia, all the while spawning genetically identical mushrooms above ground, and biologists have argued that such hyphal masses qualify as some of the largest and most ancient organisms on earth.

Most fungi are adapted to grow in cool or foresty temperatures, maybe 60, 70 degrees Fahrenheit, which is why the pathogens among them tend to prey on plants, or insects or cold-blooded animals like 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.

With their hot body temperatures, mammals and birds suffer from few fungal diseases save those confined to the coolish epidermis.

Bats are mammals, but the species now afflicted by white-nose syndrome are cave-hibernating bats, and when the bats lapse into their hibernation torpor, said David S Blehert, a microbiologist with the U S Geological Survey’s National Wildlife Health Center in Madison, Wis., their core body temperature drops down to just a couple of degrees above cave conditions, as low as 44 degrees. “This pathogen is treating the bats as if they were forgotten tubs of cottage cheese in the back of the refrigerator,” Blehert said. Moreover, the fungus appears to be unusually virulent. “We’re seeing in excess of 90 percent mortality at some sites,” Blehert added.

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