Colleen Cavanaugh, Ph.D., is a microbiologist and Edward C. Jeffrey Professor of Biology at Harvard University who has studied hydrothermal vent ecosystems for over 20 years. As a graduate student, Cavanaugh was the first to propose that the giant tube worm, Riftia pachyptila, obtains its food from bacteria living within its cells. In a process called chemosynthesis, these bacteria use the energy locked within reduced chemicals (e.g., hydrogen sulfide) to synthesize organic matter, allowing organisms such as the giant tube worm to exist on the ocean floor without sunlight.
Cavanaugh grew up in Detroit, Michigan and knew as early as second grade that she wanted to be a scientist. "In English class you had to write, in science class you didn't," she has said, "So science became my first choice." She began focusing on biology and ecology by the seventh grade and says "I thought about working on the Great Lakes, and decided to major in biology at the University of Michigan."
Her life direction was changed in her sophomore year when she heard about a course in marine ecology at the oceanographic center in Woods Hole, Massachusetts. Cavanaugh's work there involved wading out into chilly waters to study the mating habits of horseshoe crabs but still she "fell in love" with the relaxed camaraderie and exchange of ideas between biologists, geologists, and scientists from other disciplines.
Through a series of events Cavanaugh ended up stranded in the Greater Boston area looking for a job as waitress but ended up replacing a last minute dropout in a Boston University undergraduate research program and returned to her work with local horseshoe crabs. She met Phillip Gschwend, a Massachusetts Institute of Technology graduate student studying chemical oceanography, and later married him.
After graduating from the University of Michigan in 1977, Cavanaugh moved to Cape Cod to work at the Marine Biological Laboratory at Woods Hole. During the next two years, the focus of her attention shifted from Crustacea to bacteria, "creatures that impressed her for their ability to live anywhere". Ready to pursue her education, Cavanaugh applied to several graduate schools and was accepted at her first choice: Harvard.
Discovery of chemosynthesis in tube worms
Shortly after Cavanaugh began her graduate studies, she was attending a lecture by Meredith Jones, curator of worms at the Smithsonian Institution. Jones was discussing the giant tube worm, a creature which had neither a mouth nor a gut, and the challenge was to figure out how such a creature could survive. When Jones mentioned elemental sulfur crystals within the worms gut, Cavanaugh states, "It was at that point that I jumped up and said, 'Well, it's perfectly clear! They must have sulphur-oxidising bacteria inside their bodies'".
Jones apparently told her to sit down  but provided Cavanaugh with a specimen captured by a research submarine working on the bottom of the Pacific Ocean. Cavanaugh eventually proved her case and thus the Harvard Gazette describes Cavanaugh's pioneering study of these unique creatures:
As a first-year graduate student, she discovered what makes life possible in a hell-on-earth where the sun never shines, temperatures can exceed 250 degrees F, and the ocean exerts pressures of thousands of pounds on every square inch of an animal's body. Giant worms, huge clams and mussels, and strange shrimp thrive in such conditions because of one-celled bacteria who live on and inside them. The bacteria turn sulfur, methane, and other inedibles into organic molecules that their hosts feed on.
Cavanaugh went on to earn a masters degree and a doctorate degree in Biology and to find similar symbiotic partnerships among Solemyidae clams living in shallow eelgrass beds and mudflats along the New England coast and in shrimp near sub-sea springs in the middle of the Atlantic. A 2004 television mini-series hosted by Bill Nye named chemosynthesis as one of the 100 greatest scientific discoveries of all time.
This research earned Cavanaugh an M.A. in 1981, a Ph.D. in 1985, a Junior Fellowship in the Society of Fellows in 1986-89, an assistant professorship in 1989, and an associate professorship in 1993. Then in 1995, "for these discoveries and her reputation as a teacher and mentor", Cavanaugh was given tenure at Harvard and has continued to build her career on the study of hydrothermal vent ecology.
Cavanaugh believes that life on Earth may have started under similar conditions and says "the idea makes sense because some of the oldest forms of free-living bacteria show signs of being heat-loving organisms." Cavanaugh's work has made the scientific community rethink the "warm chicken soup" theory of life's origins in which the accumulation of organic molecules in shallow waters was a result of lightning electricity.
Cavanaugh's ground-breaking discoveries of the biology of the deep Pacific Ocean were made in a Cambridge, Massachusetts laboratory and she worked on marine life in the laboratory and onboard ships for twelve years before she won a place on the deep-diving submarine Alvin and went to the bottom of the Gulf of Mexico off the Florida for the first time in 1992. According to a 1996 magazine article:
Not many people have visited with 6-foot-long, bright red worms on the boiling bottom of the ocean. It sounds like a Jules Verne fantasy, but newly tenured Professor of Biology Colleen Cavanaugh has seen these and other strange creatures on voyages to the bottom of the deep sea.
She later participated in more "Extreme Expeditions"—such as a dive to a depth of 8,200 feet off the west coast of Mexico—to collect tube worms and their bacteria, the chemically-rich fluids that flow out of the vents, and mineral samples from the deep sea ocean floor. Cavanaugh, who has been called "a scientific Captain Nemo" is prominent in her field of biology and according to a 2001 Discover magazine article about a visit to "a hot crack in the Earth under the Indian Ocean":
Biologists who study the physiology of organisms are under time pressure: They must dissect the organisms before they deteriorate. Colleen Cavanaugh, a microbiologist from Harvard, needs animals that are alive and not starved; once they've been away from their vent too long, even if they've been sitting in a box on the ocean floor, they start to digest the symbiotic bacteria in which she is interested.
Cavanaugh is the discoverer of a new species of deep-dwelling mussel in the Gulf of Mexico that shares its body with symbiotic bacteria that feed on methane. She has also co-authored a research paper (supported in part by the National Oceanic and Atmospheric Administration's National Undersea Research Program and its West Coast and Polar Regions Center at the University of Alaska, Fairbanks) published in Nature about how whale corpses—and their bones in particular—that drop to the bottom of the ocean play an important role in the ecology there.
The Cavanaugh Laboratory at Harvard works on a number of projects related to bacterial symbiosis in marine invertebrates from deep sea hydrothermal vents, methane seeps, and coastal reducing sediments. Researchers there have a special interest in characterizing the metabolic and genetic capabilities of symbionts, their evolutionary relationships with free-living bacteria, and the co-evolution of symbiont and host.
- MDIBL Newsletter, Fall 2006, MDI Biological Laboratory
-  Harvard University Department of Organismic and Evolutionary Biology
-  Questions for Extreme 2003
-  University of Delaware, Interview November 2004
- Harvard University Gazette: Microbiologist-Aquanaut Colleen Cavanaugh Receives Tenure
- Kunzig, Robert, Mapping the Deep: The Extraordinary Story of Ocean Science, Norton, 2000, p. 142 ISBN 978-0-393-32063-3
-  "100 Greatest Discoveries" (2004)
-  To the Depths of Discover
-  Worm Digest
-  Discover magazine (published online December 1, 2001 )
-  Oceanographers Say Dead Whales Provide Deep-Sea Living Legacy
-  Cavanaugh Laboratory at Harvard