Study of Mud May Yield Clues
to Life on Distant Planets
ieter Visscher is looking for signs of life on distant planets. It's the logical next step - he has already studied life in the mud and water of such far-flung places as Brazil, the Dutch Antilles, and Hawaii.
Visscher, an associate professor of marine sciences, is working with scientists in chemistry, astronomy, and other disciplines, helping NASA's Astrobiology Institute look for biogenic gases in the clouds of planets outside the solar system.
Visscher currently has more than $500,000 in active grants from NASA, and more than $1 million from the Environmental Protection Agency and the National Science Foundation.
"What we're looking for are signals in the atmosphere that have a biological origin," Visscher says. He identifies biogenic gases - gases likely to be the product of biological processes - by studying earth's bacteria. He is currently looking for such gases in Mexico's salt flats and Yellowstone National Park's hot springs.
Knowing which gases may indicate the presence of life will assist NASA in identifying which planets to search for extraterrestrial life.
Visscher's cross-disciplinary work with NASA is one of a myriad projects he is pursuing. Yet all his interests are rooted in the understanding of how bacteria use and reuse chemical elements.
Bacteria have existed for 3.5 billion years, Visscher says, and are integral to the workings of the planet. "In my view the world consists of element cycles," he says. "I believe the element cycles are mainly mediated by bacteria."
Visscher's work on element cycles has important environmental implications, says Barrie Taylor, a professor of biochemistry, molecular biology, and marine and atmospheric chemistry at the University of Miami.
Understanding the role of bacteria in element cycles, Taylor adds, helps us understand what we are doing wrong or right for the environment.
Visscher's far-reaching work has a basic origin: mud, or sediment. "Bacterial activity is a lot higher in sediment than in the water column," he says.
One of the elements cycled by mud-based bacteria is sulfur, known for its pungent odor. Visscher began studying the sulfur cycle when he was an undergraduate. "Anything that smells I like," he says, "because I know there's a lot of bacterial activity."
In Visscher's lab in the new Marine Sciences Building, samples of mud are scattered among pieces of state-of-the-art equipment. One sample has a firm, gelatinous consistency. Another, though long dried out, would quickly return to life if given water.
Sophisticated equipment helps Visscher make in situ observations in the field: he observes bacterial communities in their natural context. Knowing the setting of an observation made in a specific location makes it easier to generalize, he explains.
His newest piece of equipment is designed to sit at the bottom of Long Island Sound for a day at a time, getting a picture of the environment bacteria live in, as well as measuring the elements left by the bacteria.
Some of Visscher's research explores how stromatolites, layered rocks, are formed by biofilms, networks of bacteria found in some mud. Some stromatolites, he says, are the work of bacterial communities that have been stable for 3.5 billion years.
Visscher is also studying the cycling of mercury and of methyl bromide. Previous studies, he says, may not have properly judged the influence of the oceans on these cycles.
Some have made extrapolations about mercury cycling from small, polluted bodies of water, Visscher says. And in the case of methyl bromide, a widely used fumigant being phased out owing to environmental risks, he is finding that "marine bacteria can consume methyl bromide very quickly."
The Avery Point campus is well suited for his research. "Long Island Sound is an incredible laboratory," he says. "In a very small distance, you have a variety of different ecosystems."
Visscher's teaching is permeated by his research. He emphasizes hands-on laboratory experience in his courses, and works closely with the four graduate students in his lab.
Sifting through mud and water to scrutinize tiny, ancient bacteria, Visscher may make discoveries that will have implications for faraway planets and the future of our environment.
Brent C. Evans