Book 1 Reading and Speaking (1108795), страница 4
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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 excretedigestive enzymes. But Armillaria has the unique ability to extend rhizomorphs, flat shoestringlike structures, thatbridge gaps between food sources and expand the fungus's sweeping perimeter ever more. A combination of goodgenes and a stable environment has allowed this particularly ginormous fungus to continue its creeping existenceover the past millennia. "These are very strange organisms to our anthropocentric way of thinking," says biochemistMyron Smith of Carleton University in Ottawa, Ontario.All fungi in the Armillaria genus are known as honey mushrooms, for the yellow-capped and sweet fruitingbodies they produce.
Some varieties share this tendency for monstrosity but are more benign in nature. In fact thevery first massive fungus discovered in 1992—a 37-acre (15-hectare) Armillaria bulbosa, which was later renamedArmillaria gallica—is annually celebrated at a "fungus fest" in the nearby town of Crystal Falls, Mich. Myron Smithwas a PhD candidate in botany at the University of Toronto when he and colleagues discovered this exclusivefungus in the hardwood forests near Crystal Falls. "This was kind of a side project," Smith recalls. "We were lookingat 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 relatedsiblings using a battery of molecular genetic techniques. The major test compared fungal genes for signs ofinbreeding, where heterozygous strips of DNA become homozygous.
That's when they realized they had struck itbig. The individual Armillaria bulbosa they found weighed over 100 tons (90.7 metric tons) and was roughly 1,500years old.Ironically, the discovery of such huge fungi specimens rekindled the debate of what constitutes an individualorganism. "It's one set of genetically identical cells that are in communication with one another that have a sort ofcommon purpose or at least can coordinate themselves to do something," explains Tom Volk, a biology professorat the University of Wisconsin–La Crosse. Both the giant blue whale and the humongous fungus fit comfortablywithin this definition.
So does the 6,615-ton (six-million-kilogram) colony of a male quaking aspen tree and hisclones that covers 107 acres (43 hectares) of a Utah mountainside.12And, at second glance, even those button mushrooms aren't so tiny. A large mushroom farm can produce asmuch as one million pounds (454 metric tons) of them in a year.
"The mushrooms that people grow in themushroom houses - they're nearly genetically identical from one grower to another," Smith says. "So in a largemushroom-growing facility that would be a genetic individual—and it's massive!" In fact, humongous may be in thenature of things for a fungus. "We think that these things are not very rare," Volk says. "We think that they're in factnormal." (From Scientific American Online, October 4, 2007)Text B. Seedy but Speedy: Fungus Spews Spores at 55 MphBy Susannah F. LockeIn a finding that could help control harmful fungus, researchers have discovered a high-speed mechanismthe germs use to project their spores into the air. Scientists from Miami University (M.U.) in Oxford, Ohio, and theCollege of Mount St.
Joseph in Cincinnati report in the journal PLoS ONE that fungi may be one of the fastest landspecies, clocking speeds of up to 55 miles (88 kilometers) per hour and producing accelerations 180,000 timesgreater than gravity.Fungi are the most common crop pathogens in the world. Most are fairly harmless to people, although likeother allergens they sometimes exacerbate allergies and asthma. But certain varieties such as Stachybotryschartarum, commonly referred to as black mold, that thrive in damp places like basements may also infect thelungs of people who have compromised immune systems or chronic bronchitis.
Biologists once believed that mildair currents were enough to release fungi's spores, but are increasingly finding that molds employ elaboratemethods to spew their seeds away from the nest. Using ultrahigh-speed video, the researchers calculated thatsome 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 andother herbivore dung. These species play a critical role in the ecosystem by breaking down waste to recycle itsnutrients into the soil.
The fungi project their spores away from the resident dung because cows will not eat nearfeces. 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 theair, trailing glistening liquid behind them.
The researchers used the video to clock the spores speeding along at 55mph. The team also identified how several fungi build up water pressure to power a spore launch. First, the fungiaccumulate sugars and other small molecules in their cells, which, in turn, brings in more water. Targeting the firststep of this process could be a key to developing new fungicides. "By understanding the basic mechanism," hesays, "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?Exercise 5. Earlier you discussed parasitic fungi. Now read the article which describes one exampleof multi-species relationship in detail.Fungus genome boosts fight to save North American forestsDNA sequence could advance efforts to control pine beetle infestations.By Elie DolginCanadian researchers have decoded the DNA of the tree-killing fungus found in the mouths of mountain pinebeetles, the destructive bugs that wipe out entire North American forests.
Further genome sequencing of the beetleand pine tree species should help forest managers design better pest-control tactics, the authors say. "It's reallygetting to a systems-level understanding of the mountain pine beetle epidemic," says study co-author JörgBohlmann, a chemical ecologist at the University of British Columbia in Vancouver, Canada, who is leading themulti-species genome initiative. "What really happens in nature is not confined to one species, but is happening atthe intersection when one species interacts with another."Mountain pine beetles (Dendroctonus ponderosae) have eaten their way through vast swathes of westernNorth American pine forests, including around 15 million hectares in British Columbia alone.
As the burrowingbeetles tunnel under the bark to feed and lay eggs, they release spores of the blue-stain fungus (Grosmanniaclavigera), which stops the production of a protective toxic resin released by the tree and allows the beetles tocontinue to infest.Bohlmann and his colleagues assembled the fungus's 32.5-million-base-pair genome, which is around ahundredth the size of the human genome, using a combination of next-generation and traditional sequencing13technologies — the first time that a complex eukaryotic organism has been sequenced from scratch using such ahybrid approach.
The genome was reported online this month in the journal Genome Biology.For the other two species — the beetle and the tree — the researchers are concentrating mainly onexpressed gene sequences, fragments of the complete DNA sequence, rather than the genomes in their entirety.They've already amassed one of the largest insect libraries of gene transcripts for the bark beetle from more than adozen beetle life stages and body parts. The lodgepole pine (Pinus contorta) and jack pine (Pinus banksiana) arestill at a much earlier stage of sequencing.The goal, says Dezene Huber, a chemical ecologist at the University of Northern British Columbia in PrinceGeorge, Canada, is to predict the dynamics between the organisms under various climatic conditions.
"We shouldbe able to look at particular genes and say which population of trees is interacting with which population of fungusand which population of beetles," he says. "It's really going to push science in a big way," says Brian Aukema of theCanadian Forestry Service in Prince George, who plans to incorporate the genomic data into landscape ecologicalmodels. "Once you have that information, you can hopefully feed that into models and understand where thesebeetle populations might be the most susceptible to treatments, intervention strategies and mitigation."Multi-species genomic interactions have been studied for some human diseases, including malaria, and afew symbiotic ecological relationships such as leaf-cutter ants and their microbial partners, but the approach hasnever before been applied on this scale for an outbreaking forest nuisance.Already, the University of British Columbia researchers, led by mycologist Colette Breuil, have taken thefungus genome, pinpointed the gene responsible for staining the pine wood blue and created a knockout strain thatdoes not produce any pigment.
The blue staining reduces the commercial value of affected timber, but it is not clearwhat role the colouring plays in driving infestation. The researchers are now testing this strain to tease that apart.But the full utility of the fungus genome might only be realized after other related species are alsosequenced, says Diana Six, who studies the interaction between bark beetles and fungi at the University ofMontana in Missoula.
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