Nov. 17, 1998 ATHENS, Ga. -- Poet Robert Frost famously wrote that "some say the world will end in fire, some say in ice." Though scientists can make educated guesses at the final convulsions of the planet, they are far more comfortable searching for its origins. New evidence, discovered in the past decade, now indicates that life on Earth may have originated close to the fire down below.
Indeed, hyperthermophiles -- the extreme heat-loving microorganisms that flourish at and above the boiling point of water -- could be a key to unlocking both evolution and the origin of life itself.
"It appears from studies of these organisms that life did begin in shallow pools with highly elevated temperatures, but once life appeared, perhaps 90 to 99 percent was destroyed again, and there was a constant disappearing and evolving," said Juergen Wiegel, a microbiologist at the University of Georgia. "A lot of different evolutionary roots probably came from the same pools."
The arguments concerning thermophiles by Wiegel and numerous other scientists from around the globe were just published in Thermophiles: The Keys to Molecular Evolution and the Origin of Life? by Taylor & Francis publishers. The book, edited by Wiegel and UGA biochemist Michael W. Adams, publishes information first presented at a workshop on the University of Georgia campus in 1996.
The event at UGA was unusual because international experts in a number of different fields came together to discuss the implications of thermophile research. Researchers in biology, genetics, biogeochemistry, oceanography, systematics and evolution joined for the meeting.
"The conference was very significant for the thermophile field, which is so rapidly developing," said Adams, whose research in the area has drawn considerable international interest this decade. "There has been a major expansion in the study of thermophiles in the past five years, though much more in Japan and Europe than in the U.S."
Science has long known that some microorganisms flourished at high temperatures. As early as 1924, a researcher suggested that the first forms of life were thermophiles that had originated in hot springs. But scientists did not speculate on the existence of hyperthermophiles until less than two decades ago. These organisms prosper at temperatures near and even at 100-degrees Celsius, the boiling point of water. Even more important, perhaps, scientists led by Carl Woese of the University of Illinois, used a cutting-edge technique to discover that hyperthermophiles are the most slowly evolving of all extant life forms. These facts together led many scientists to conclude that life may first have evolved on Earth under hyperthermophilic conditions.
In a sense, it's not surprising that important discoveries about the origins of life are coming from microorganisms, since they are so varied.
"Some bacteria are much farther apart on the phylogenetic scale from other bacteria and archaea than humans are from plants," said Wiegel. "Man is much, much more closely related to the cockroach than most bacteria are to other bacteria."
Indeed, science may know less than one percent of the existing species of microbes on Earth while knowing probably 99 percent of all animals and more than 95 percent of all plants. Bacteria that flourish in hot conditions, in fact, can be found nearly everywhere, from the soil to compost heaps. But the ones that live under the most extreme conditions of heat may reveal more to science about the origins of life.
While a number of the chapters argue that life might have begun in conditions such as those now found in hot springs or in undersea thermal vents, the book is not unanimous on this point. In fact, a chapter written by Stanley Miller of the University of California, La Jolla and Antonio Lazcano of the University of Mexico argues that life did not and could not have begun at the growth temperatures of hyperthermophiles.
"Today we know that such extrapolations into the distant past merit considerable caution," they wrote. "We are far from understanding the origin and characteristics of the first living beings, which may have lacked even the most familiar features found in extant cells . . ."
Patrick Forterre of the University of Paris-South agrees, claiming that the hot-origin-of-life scenario has an Achilles heel and should be investigated much more before being accepted by the scientific community. Others, such as John Baross of the University of Washington, feel that strong evidence exists in the geological record to support a thermophilic theory of origins.
G¸nter W”chtersh”user from Germany writes what Wiegel calls "an elegant and stimulating chapter," arguing for a hyperthermophilic origin of life in an iron-sulfur primordial world. He proposes that life began with metabolism on surfaces.
While scientists debate the issues surrounding thermophiles, businesses are clearly finding the heat-loving bacteria useful. From detergents to industrial-scale applications, thermophiles are the darlings of numerous new processes, and their value as catalysts is growing almost by the day.
"A hyperthermophilic origin for life on this planet is not universally accepted," said Adams and Wiegel in their preface for the book. "What one can conclude from this collection of chapters is that answering such fundamental questions as how life first originated and whether it did so under high-temperature conditions requires insight and perspective from a range of disciplines."
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