Petit and Tangley_lec3 - US News and World Report — issue...

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Unformatted text preview: US News and World Report — issue dated November 8, 1999 “The invisible emperors Microbes, not man, are the real powers on Earth” BY CHARLES W. PETIT AND LAURA TANGLEY Salmonella in eggs, E. coli in burgers, campylobacter in poultry, and that‘s just for starters. It's easy to think that bacteria and other germs are around us, on us, and in us just to make us miserable. Think again. Sure, some of the little critters are vile, but most are leaving scientists awestruck, as new tools let them spy for the first time on microbes in their native habitats. They see a wonderland, a mother lode of evolution containing entire, previously unknown, kingdoms of life. Indeed, Earth's microscopic hordes make the rest of life possible; their sheer mass, vitality, and variety dwarf that of the readily visible world. Most are not only harmless but oblivious to people, who cannot survive without them. Increasingly, however, humans are paying attention. Scientists are mining the microbial world for potential cancer cures; one lowly microbe helped spawn a revolutionary technique to replicate DNA. Research on microbes is even changing our understanding of the nature of life—and perhaps its origins. The famed Harvard University evolutionary biologist Edward O. Wilson, who has spent much of his career exploring the intricate worlds of ants, says that if he were starting over today he would study microbes: "The microbial world is without limit." Norman Pace, a microbiologist at the University of Colorado—Boulder, agrees. "We were and are a microbial planet," says Pace, who seeks greater efforts to understand microbes, which he calls the "real show" in biology. For the first 3 billion of the 3.8 billion years since life arose, microbes were Earth's only residents. In his office, Pace grabs a bottle of yellow muck taken from a salty pond near San Francisco. Each Spoonful, he says, holds billions of individuals and thousands of uncataloged species ~"Amazons of biodiversity." Nobody knew that creatures such as bacteria and viruses even existed until 1674 when Dutch linen maker Antony van Leeuwenhoek put murky lake water beneath two lenses. He notified the Royal Society in London of myriad, tiny creatures he called "animalcules." Until recently, the only way to identify microbes was to grow colonies in the laboratory. But fewer than 1 percent of these organisms will grow in lab cultures. As for the rest, science only knew that there are scads of them. How many? Health standards say raw food is safe if it has only 5 million bacteria per gram. A University of Georgia team last year published a mind—blowing stab at the global population of prokaryotes, a category of single—celled creatures that includes bacteria: roughly 5 million trillion trillion (a five followed by 30 zeros). They have 10 times the living protoplasm of all the world's animals. Dried, they would cover France 3 feet deep. "This is a huge amount of biology we don't understand," says William Whitman, a microbiologist who led the Georgia study. "Our ignorance is immense." The expanding field of microbial research includes a just-started, $2.5 million—per—year program by the National Science Foundation to set up more than a dozen microbial observatories. Sites for study include Yellowstone hot springs, Mono Lake in California, Minnesota prairie soil, California scrub lands, an island off Cape Cod, an Oregon forest, the. Atlantic near Bermuda, and the deserts of Arizona. (On November 9, PBS launches a four-part series on microbes, Intimate Strangers: Unsecn Life on Earth. See US. News Online, . ) In a mote of dust: Today's microbe hunters work harder than Dr. Seuss's Horton the Elephant, whose big ears discovered the Who civilization on a dust grain. Take Edward DeLong, a microbiologist at the Monterey Bay Aquarium Research Institute, who has found scores of new species in mud flats, deep—sea sediments, the open ocean, and on Antarctica‘s frozen shore. At his lab in Monterey, Calif, DeLong runs mud from 3,000 feet below sea level through centrifuges, then filters, and treats it with chemicals that dissolve the microbes embedded within. Their DNA floats free, a cocktail of genetic csscnccs. Using the latest tools of biotechnology, he and his co—workers separate the genes and compare their DNA sequences to genes of known microbial classes. Later, they put fluorescent tags on the more distinct DNA and put it back in the mud, where it sticks to members of parent species and makes them light up. "It's the reverse of traditional biology, where we spot a new creature and then analyze its DNA," says DeLong. "Now we get the DNA first, then find what made it." Every time, he adds, "we find something new." Without microbes, there would be no food to eat or air to breathe: Algae and bacteria, through the process of photosynthesis, produce up to half the atmosphere‘s oxygen. Natural residents of the human body (box, Page 74), microbes help digest food, produce essential vitamins, and protect us from other organisms that cause disease. Outside the body, bacteria and fungi break down dead plants and animals, as well as other natural and manmade wastes, keeping the world from filling up with garbage. In the process, they recycle life—sustaining sulfur, nitrogen, carbon, and other nutrients and minerals that keep the planet running. Even before anybody knew what they were, people harnessed microbes to stay healthy, clean, and fed. The yeast Saccharomyces cerevisiae is key to making bread, beer, and wine. Leuconostoc bacteria turn milk into cream cheese. And microbes have long been a source of disease—fighting antibiotics, including penicillin, erythromycin, and streptomycin. Many scientists also believe that human origins lie in simple bacteria, which invaded or ingested each other and evolved into complex organisms. Mitochondria, the parts of plant and animal cells that process energy, are thought to be bacterial descendants. But microbes never seem to get the respect they deserve. In fact, society's phobia about bacteria and other ”germs" has spawned what some scientists say is an overuse of antimicrobial agents—found in everything from hand and dishwashing soap to toothbrushes, children's toys, and cat litter—that threatens to upset nature's balance of microbial flora and, ultimately, harm humans. "Over millennia, we've evolved with and accommodated countless microbial species that protect us from the few that cause harm," says microbiologist Stuart Levy, director of the Center for Adaptation Genetics and Drug Resistance at Tufts University School of Medicine. Levy fears that, once people kill off their competitors, dangerous new pathogens may take hold. Other scientists are more excited about "extremophiles," microbes that thrive in environments once considered uninhabitable, from boiling-hot, deep—sea volcanoes to frozen lakes buried beneath Antarctic ice sheets. They are largely Archaea, a domain of life first identified 20 years ago by Carl Woese, a microbiologist at the University of Illinois. By analyzing ribosomal RNA, Woese concluded that, aside from eukaryotes (a domain that includes humans and other creatures big enough to see) and bacteria, there was a third, "ancient" domain, reflecting a three—way partition of life that occurred billions of years ago. Woese's radical declaration of the third domain of life—microbial but as different from bacteria as we are-is only now widely accepted. Bacterial gold: Extremophiles include microbes that love heat (thermophiles), cold (psychrophiles), Salt (halophiles), and even acidity (acidophiles). Others not only survive but prosper under toxic concentrations of heavy metals or other poisons and at radiation levels 1,000 times higher than any human could withstand. Understanding how the bugs endure such harsh conditions may help in the search for‘compounds to fight cancer and other diseases, says marine biologist Richard Lutz of Rutgers University, who is collecting extremophiles from deep—sea hydrothermal vents to look for chemicals that could kill cancer cells and viruses. Similar expeditions have yielded microbial gold: In the 1980s, scientists discovered in a Yellowstone hot springs microbe a heat—resistant enzyme crucial to the development of a technique, polymerase chain reaction, that allows biotechnologists to replicate DNA and has become the basis of a billion—dollar industry. Cornell University astronomer Thomas Gold even believes that the bulk of life on Earth consists of what scientists consider extremophiles: microbes far beneath the planet's surface that feed on hydrocarbons bubbling up from the depths. In his new book, The Deep Hot Biosphere, Gold cites evidence of native microbes in samples from oil wells 3 miles deep. "What we call extreme environments,” he says, "are the borderlands between surface and subsurface worlds. And what we call extremophiles are ambassadors from that other, more dominant, world." Gold and a few other researchers believe life first arose in such hellish depths, rather than in the cozy "primordial soup" of sunlit, surface waters as conventional biologists have assumed. Gold says that "surface chauvinism" has so far kept scientists from discovering life on other planets: While conditions today on Earth's surface are most likely extremely uncommon in the universe, he believes subsurfaces friendly to life are the norm. Thinking along the same line, National Aeronautics and Space Administration scientists spent six weeks this summer drilling the permafrost of northern Siberia for microbes that may be living in conditions similar to Mars or Europa, one of Jupiter's moons. Near the Earth's other pole, U.S., French, and Russian researchers plan to drill into Lake Vostok—a Lake Ontario—size body of water deep under the Antarctic ice cap-to see if microbes live there. Though Harvard biologist Wilson has not lost his reverence for visible organisms, the most challenging ecology, he says, is literally underfoot: "It is possible to spend a lifetime in a Magellanic voyage in a trip around the trunk of a single tree." ...
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