Mapping the Geography of Symbiosis

By di Properzio, James | The World and I, August 2002 | Go to article overview

Mapping the Geography of Symbiosis


di Properzio, James, The World and I


Wherever she looks--in the mud, the air, the cells of plants and animals, termite guts, or the tails of sperm--Lynn Margulis sees evidence of ancient microbial mergers or primary ongoing microbial activity sustaining life at all levels.

Nineteen-year-old Lynn Sagan saw amoebae for the first time through a high-quality microscope in a laboratory at the University of Wisconsin, Madison, where she was a graduate student in genetics. "I really liked amoebae," Lynn Margulis reminisces fondly. "I still do."

Working with the amoebae changed her life and helped define the focus of her subsequent scientific research. How does one take care of amoebae? "They tend to stick to the bottom of an open bowl, if they are healthy. They are fed ciliates [unicellular microbes covered with short, whiplike extensions], which are grown separately and added every day to their bowl. When a drop of food is added, they are activated; changing shape all the time, they flow toward the food, which they engulf. A struggle ensues; the actively swimming ciliate is subdued by digestive enzymes leaked into the food vacuole." This drama, which Sagan monitored in the lab every afternoon and early evening, had the precision and excitement of a lion hunt. "Well-fed amoebae," she says, "round up and proceed to reproduce by division in half an hour or forty-five minutes, and they reproduce on average once a day. Many more are produced than can possibly survive.

"If you don't clean them, they die," Margulis remembers. "Aspiration is crucial." She would use an aspirator to remove the top layer of dirty water and unhealthy or dead amoebae, reducing the volume of the bowl by about half. Then she would add a balanced salt solution made with double-distilled water. Margulis recalls this dirty work with great fondness: "I owe my passion for working on Saturday nights to the utter necessity of amoeba feeding and bowl cleaning every day," she insists.

Today, at age 64, Margulis is still focusing on and promoting microbes. To a science, taxonomy, that originated from naked-eye observations, she helped to bring a five-kingdom classification based on microscopic distinctions within the basic cell of each type of life. She has further shown that the symbiotic intertwining of life extends all the way from the microscopic level to the planetary level. Now, Margulis' latest theory offers the provocative claim that symbiosis, and not random mutation, is the wellspring of evolution.

The microcosm's spokesperson

Awake before the birds are singing, cycling to work before cars are on the road, and peering down a microscope at the open guts of termites before the doors to the building at her laboratory at the University of Massachusetts at Amherst are unlocked, Margulis has the energy of the swimming bacteria she so adores. Her ninth book, Acquiring Genomes: A New Theory of Evolution, was published in July, and she has authored or coauthored hundreds of scientific articles and dozens of popular essays. In addition, Margulis is a dedicated teacher and a keen scientific investigator of microorganisms. A geneticist by training and now distinguished university professor in the Department of Geosciences at the University of Massachusetts, she describes herself as a "spokesperson for the microcosm."

In championing the microbes, Margulis has made several significant contributions to our understanding of evolution. Her "endosymbiotic hypothesis," which states that the mitochondria in every animal cell and the plastids in algae and plants are actually different kinds of remnant bacteria that live symbiotically, is now included in every college biology textbook. She has spent a good portion of her career finding evidence for this idea--that components of plants and animals were once free-living bacteria that joined symbiotically with other free-living bacteria early in the evolution of life.

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