Text A. The Largest Organism on Earth Is a Fungus

The blue whale is big, but nowhere near as huge as a sprawling fungus in eastern Oregon

By Anne Casselman

Next time you purchase white button mushrooms at the grocery store, just remember, they may be cute and bite-size but they have a relative out west that occupies some 2,384 acres (965 hectares) of soil in Oregon's Blue Mountains. Put another way, this humongous fungus would cover 1,665 football fields, or nearly four square miles (10 square kilometers) of turf. The discovery of this giant Armillaria ostoyae in 1998 heralded a new record holder for the title of the world's largest known organism, believed by most to be the 110-foot- (33.5-meter-) long, 200-ton blue whale. Based on its current growth rate, the fungus is estimated to be 2,400 years old but could be as ancient as 8,650 years, which would earn it a place among the oldest living organisms as well.

A team of forestry scientists discovered the giant after setting out to map the population of this pathogenic fungus in eastern Oregon. The team paired fungal samples in petri dishes to see if they fused, a sign that they were from the same genetic individual, and used DNA fingerprinting to determine where one individual fungus ended.

This one, A. ostoyae, causes Armillaria root disease, which kills swaths of conifers in many parts of the U.S. and Canada. The fungus primarily grows along tree roots via hyphae, fine filaments that mat together and excrete digestive enzymes. But Armillaria has the unique ability to extend rhizomorphs, flat shoestringlike structures, that bridge gaps between food sources and expand the fungus's sweeping perimeter ever more. A combination of good genes and a stable environment has allowed this particularly ginormous fungus to continue its creeping existence over the past millennia. "These are very strange organisms to our anthropocentric way of thinking," says biochemist Myron Smith of Carleton University in Ottawa, Ontario.

All fungi in the Armillaria genus are known as honey mushrooms, for the yellow-capped and sweet fruiting bodies they produce. Some varieties share this tendency for monstrosity but are more benign in nature. In fact the very first massive fungus discovered in 1992—a 37-acre (15-hectare) Armillaria bulbosa, which was later renamed Armillaria gallica—is annually celebrated at a "fungus fest" in the nearby town of Crystal Falls, Mich. Myron Smith was a PhD candidate in botany at the University of Toronto when he and colleagues discovered this exclusive fungus in the hardwood forests near Crystal Falls. "This was kind of a side project," Smith recalls. "We were looking at the boundaries of [fungal] individuals using genetic tests and the first year we didn't find the edge."

Next, the microbiologists developed a new way to tell an individual apart from a group of closely related siblings using a battery of molecular genetic techniques. The major test compared fungal genes for signs of inbreeding, where heterozygous strips of DNA become homozygous. That's when they realized they had struck it big. The individual Armillaria bulbosa they found weighed over 100 tons (90.7 metric tons) and was roughly 1,500 years old.

Ironically, the discovery of such huge fungi specimens rekindled the debate of what constitutes an individual organism. "It's one set of genetically identical cells that are in communication with one another that have a sort of common purpose or at least can coordinate themselves to do something," explains Tom Volk, a biology professor at the University of Wisconsin–La Crosse. Both the giant blue whale and the humongous fungus fit comfortably within this definition. So does the 6,615-ton (six-million-kilogram) colony of a male quaking aspen tree and his clones that covers 107 acres (43 hectares) of a Utah mountainside.

And, at second glance, even those button mushrooms aren't so tiny. A large mushroom farm can produce as much as one million pounds (454 metric tons) of them in a year. "The mushrooms that people grow in the mushroom houses - they're nearly genetically identical from one grower to another," Smith says. "So in a large mushroom-growing facility that would be a genetic individual—and it's massive!" In fact, humongous may be in the nature of things for a fungus. "We think that these things are not very rare," Volk says. "We think that they're in fact normal." (From Scientific American Online, October 4, 2007)

Text B. Seedy but Speedy: Fungus Spews Spores at 55 Mph

By Susannah F. Locke

In a finding that could help control harmful fungus, researchers have discovered a high-speed mechanism the germs use to project their spores into the air. Scientists from Miami University (M.U.) in Oxford, Ohio, and the College of Mount St. Joseph in Cincinnati report in the journal PLoS ONE that fungi may be one of the fastest land species, clocking speeds of up to 55 miles (88 kilometers) per hour and producing accelerations 180,000 times greater than gravity.

Fungi are the most common crop pathogens in the world. Most are fairly harmless to people, although like other allergens they sometimes exacerbate allergies and asthma. But certain varieties such as Stachybotrys chartarum, commonly referred to as black mold, that thrive in damp places like basements may also infect the lungs of people who have compromised immune systems or chronic bronchitis. Biologists once believed that mild air currents were enough to release fungi's spores, but are increasingly finding that molds employ elaborate methods to spew their seeds away from the nest. Using ultrahigh-speed video, the researchers calculated that some fungi use their own natural water pressure like squirt guns to eject their spores.

Lead study author Nicholas Money, a fungus biologist at M.U., studied fungi that grow on cow patties and other herbivore dung. These species play a critical role in the ecosystem by breaking down waste to recycle its nutrients into the soil. The fungi project their spores away from the resident dung because cows will not eat near feces. By shooting them up to eight feet (2.5 meters) away, a grazing animal will be more inclined to eat them, thereby spreading the fungal spawn via its own manure.

The research video camera shot 250,000 frames per second to capture fungi spurting their spores into the air, trailing glistening liquid behind them. The researchers used the video to clock the spores speeding along at 55 mph. The team also identified how several fungi build up water pressure to power a spore launch. First, the fungi accumulate sugars and other small molecules in their cells, which, in turn, brings in more water. Targeting the first step of this process could be a key to developing new fungicides. "By understanding the basic mechanism," he says, "you might find ways to remediate a mold-damaged home." (From Scientific American Online, September 17, 2008)

Exercise 4. Answer the following questions using the information from the texts:

1. What animal is generally considered the biggest organism on earth?

2. What extraordinary characteristics does the discovered Armillaria ostoyae fungus possess?

3. Why is Armillaria ostoyae characterized as a pathogenic fungus?

4. What conditions allowed the fungus to grow to such enormous size?

5. How can scientists distinguish an individual from a group of closely related siblings?

6. What effect do fungi produce on people and the environment?

7. What mechanisms does Stachybotrys chartarum black mold use to spurt its spores into the air?

8. Why do fungi have to employ such complicated techniques?

Date: 2016-03-03; view: 1697