Abelson Advancing Science Seminar at AAAS Explores the Planet of the Microbes

Derek R. Lovley

A visitor to Earth during most of the planet's history would have been greeted only by microbes, and those ubiquitous organisms continue to help shape both the planet's destiny and ours, according to researchers who spoke at the 26 October Philip Hauge Abelson Advancing Science Seminar at AAAS.

"It's definitely time for microbes to have their due," said David Stahl, a professor of environmental engineering and science at the University of Washington and a keen student of the microbial world. "We live on the planet of the microbes," he said, with very large numbers of those organisms controlling the key cycles of planetary chemistry that produce such essentials to life as oxygen and organic forms of carbon and nitrogen.

But in many cases, he said, scientists still don't know which populations of bugs are in control of specific cycles. There have been surprising discoveries just within the past few years. An anaerobic organism that digests ammonia, first described in 1999, represents a major part of the nitrogen cycle that had been missed during a century of investigation, according to Stahl. Another bug, discovered in 1992, turns out to account for about 20% of the bacterial component of the plankton that drifts in ocean waters.

Speakers at the symposium told how genomics, microbiology, mineralogy, geochemistry and materials science have been providing new insights on the history of microbes and their potential for such practical applications as cleaning up polluted sites, mitigating the effects of climate change or producing electricity.

The seminar, "Microbes, Minerals and the Environment," honored the late Philip Abelson, editor of Science for 22 years and then senior adviser to AAAS. He founded and sponsored the seminar series to encourage participants to think about where science is going, not where it has been.

Studies of microbes in laboratory cultures generally do not say much about the natural history of the organisms or the complex systems in which they live in the real world, Stahl said. Such studies also are biased by the fact that most microorganisms simply do not grow in conventional culture media. But new techniques for finding microbes in the wild have been paying off, he said, including random searches for interesting genetic fragments in seawater that have yielded new clues about the tremendous variety of marine microorganisms.

Anna-Louise Reysenbach

"We're so lucky to work on a diverse group of organisms that we know so little about," said Anna-Louise Reysenbach, a professor of microbial biology at Portland State University who has been studying the heat-loving microbes found around hydrothermal vents, sea-floor geysers that spew super-hot, mineral rich water. She showed an image of one organism, which she calls the "devilheterotrophventblob," whose cell wall had formed two horn-like structures. It turns out to be the first truly acid-loving microbe in the neighborhood of such hydrothermal vents.

While researchers search for new microbes in exotic locales, some of the bugs much closer to home are just as mysterious, according to Stahl. "Our gut is like the Amazon basin before the period of discovery," he said. "We know less about our gut than we do about the animals in the local zoo." Should humans ever make it to Mars, "it's not going to be one species stepping out on the surface," he said. "It's going to several thousand species."

The durability and variety of microbes continue to astonish researchers. Keynote speaker Derek R. Lovley, a microbiologist at the University of Massachusetts, Amherst, mentioned Strain 121, a deep-sea organism discovered in 2003 that survives at 121 degrees Celsius (250 degrees Fahrenheit). That is the highest temperature at which life is known to exist--equivalent to the heat in autoclaves used to sterilize surgical instruments.

Species of bacteria called Geobacter are of interest because of their novel abilities to transfer electrons. They can harvest electricity from aquatic environments and may prove useful as power sources for underwater monitoring instruments, Lovley said. It is likely that fuel cells can be made from pure cultures of Geobacter organisms, he said, perhaps to power electronic gadgets like cell phones initially. Toyota also has been funding Lovley's team with an eye toward use of microbial fuel cells in cars a few decades from now.

There are other practical applications on the horizon for microbes, speakers said, including use of Geobacter species and other microbes to bind uranium, plutonium and other metals in polluted groundwater or soils.

But Bruce Hungate, an ecologist at Northern Arizona University, offered a cautionary note on one proposed "biological fix" for rising carbon dioxide levels in the atmosphere. While studies suggest that plants will grow more in response to elevated CO2 levels, Hungate said, microbes in the soil apparently have a reverse effect, limiting the amount of carbon that the soils can sequester. "The carbon sink in soil may be somewhat exaggerated," Hungate said.

Farooq Azam

Scientists also are studying the role of microbes in maintaining a healthy "biogeochemical state" of the oceans in response to climate changes. "It is critical to know what microbes are there," said Farooq Azam, a marine microbiologist at the Scripps Institution of Oceanography in San Diego, and how their activities influence the structure and function of marine ecosystems. Only then, he said, will scientists be able to really understand the impact of rising air temperatures on ocean systems or the impact of proposed efforts to perturb the ocean ecosystem with iron to encourage plankton blooms that could soak up excess carbon dioxide emissions.

Paul Falkowski, a professor in the Institute of Marine & Coastal Sciences and Dept. of Geological Sciences at Rutgers University, was wary of human tinkering with natural cycles. "We are messing with something we don't really know much about," Falkowski said. "Human beings have only been on this planet for about 200,000 years. We have, in the last 150 to 200 years, so critically altered the carbon, phosphorus, sulfur, nitrogen, water cycles," he said, that society is on a path toward unsustainable development. He called for reductions in carbon dioxide and sulfur emissions and in the use of nitrogen-containing fertilizers so that we can return to a world "where microbes basically are taking care of the cycles for us, because we cannot take care of the cycles for ourselves." Regarding the microbes, he added: "They don't need us. We need them."

Earl Lane

29 November 2006