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Marine microbes point to ocean diversity

By LIDIA WASOWICZ, UPI Senior Science Writer   |   Feb. 6, 2002 at 4:16 PM   |   Comments

MOSS LANDING, Calif., Feb. 6 (UPI) -- Ocean explorers equipped with genetic tools once reserved for the laboratory petri dish have uncovered never-before-seen light-using marine bacteria, revealing an unexpected diversity that may require oceanographers to reconsider how marine ecosystems function.

Taking genomic techniques to the sea is an important step toward parting the waves of mystery surrounding the identity and, even more importantly, the ecological roles of microbes, whose numbers in the ocean surpass those of stars in the sky by a 100 million-fold -- but which are less understood, the scientists said.

Their report describing new and diverse groups of photosynthetic bacteria found in plankton from Monterey Bay and the central Pacific Ocean north of Hawaii is published in the British journal Nature.

The microbes -- unrelated to any previously known types -- live in the upper ocean where light and oxygen abound. They harvest energy needed for growth and survival from sunlight and, in turn, provide energy and nutrients to the rest of the food chain.

"Microbes in particular represent the organisms that are responsible for maintaining all the major energy and nutrient cycles on Earth," said lead author Edward Delong, a microbiologist at the Monterey Bay Aquarium Research Institute in Moss Landing, Calif. "Since we know that man is impacting the environment more heavily now than ever in our history, it becomes increasingly important to better understand ecosystem dynamics, ecology and biogeochemical cycles."

The road to such understanding is being paved with new technologies, scientists told United Press International.

"These new analytical approaches are letting us see for the first time some of the basic properties and characteristics of some of the most abundant organisms on the planet -- planktonic microbes," Delong said. "It's a true discovery period, and these discoveries are helping us to better understand the structure and function of the oceanic ecosystem, the living ocean."

Delong and colleagues from The Institute for Genomic Research in Rockville, Md., analyzed the microbes' genetic blueprints using genomic DNA sequencing techniques, which are yielding complete maps of heredity of a growing number of organisms, from a microscopic worm to man. They found bacterial photosynthetic genes, previously disregarded as insignificant in marine plankton, are actually widely distributed in ocean waters.

Scientists have long considered phytoplankton -- "plant" plankton that contains the green pigment chlorophyll -- to comprise the main ocean-dwelling population that turns sunlight into food. Now, it appears there also are ecologically significant groups of photosynthetic plankton that do not contain the chlorophyll found in green plants. The existence of these new types of so-called phototrophs, organisms that get energy directly from light, is forcing oceanographers to rethink and revise their models of oceanic food webs, scientists said.

"We now recognize fewer than 10 percent of the bacteria in nature so the book on biology and ecology will surely need to be re-evaluated and probably rewritten once we have a full inventory of life forms in the sea," said David Karl of the University of Hawaii in Honolulu, who wrote an accompanying News and Views article.

New technologies are enabling scientists to characterize large portions of the genomes of naturally occurring microbial species without having to grow them in laboratory dishes, a previous prerequisite for studying the life forms, scientists said.

"Even in the very first applications of these approaches, we are finding unexpected surprises," Delong told UPI

This and a spade of other recent studies unveiling previously unknown microbes are churning up new ideas on the role of marine ecosystems, especially in relation to ocean nitrogen and carbon cycles.

"The stakes and the level of excitement in the subdiscipline of microbiological oceanography are at all-time highs," Karl said. "The importance and the stakes are knowledge and understanding. If we do not have a full inventory of life forms on the planet, how can we, as scientists, answer questions from the public and from our decision makers about pollution, land-use practices and global environmental change?"

"This research will, I believe, lead to more attention being given to marine microorganisms which though invisible to the naked eye are largely responsible for the air we breathe (they supply the oxygen) and much of the food we eat (they serve as the base of most marine food webs)," Karl told UPI. "Since the oceans cover nearly three-fourths of our planet, these are issues of major proportion."

The finding will likely capture fewer headlines than would the discovery of a new species of mammal, but is nevertheless much more significant, scientists said.

"Most of the earth's biodiversity resides in microbes, especially bacteria," Karl said. "With each discovery of a new group of bacteria comes the possibility of the discovery of a new metabolic pathway, or means of processing carbon and energy. This would probably not be the case for the discovery of a new mammal which likely would be built around a well-known mode of behavior and physiology."

Much work lies ahead for even with the newly discovered microbes, many questions remain.

"We now know that they are present, but we don't know their ecological niche," Karl said. "This is work in progress."

The task ahead is, in part, to look back.

"Microbes have been around on Earth over 3.5 billion years now, and over that period of time they have been evolving and adapting," Delong noted. "They live in almost any conceivable habitat you can think of, from boiling hot springs to Antarctic ice."

The microbes' great variety endows them with scientific appeal.

"The more we learn about the diversity of life on earth, all habitats, the more reliable will be our predictions about life elsewhere in the universe," Karl said. "As it turns out, one need not go to the ends of the earth to discover new and different forms of life ... Novel microbes present themselves to us in the relatively benign sea surface around the globe. But in reality, the sea is a very extreme environment in itself and it has led to a radiation of life forms and now represents perhaps one of the most diverse habitats on earth."

© 2002 United Press International, Inc. All Rights Reserved. Any reproduction, republication, redistribution and/or modification of any UPI content is expressly prohibited without UPI's prior written consent.
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