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Immunology and Microbiology WOMI2.tpgs 5/8/03 6:01 PM Page 1 AND IMMUNOLOGY MICROBIOLOGY WORLD of WOMI2.tpgs 5/8/03 6:01 PM Page 3 AND IMMUNOLOGY MICROBIOLOGY WORLD of Brigham Narins, Editor Volume 2 M-Z General Index womi_M 5/7/03 7:52 AM Page 359 M • against antigens) in the treatment of the disease. MacLeod also MMacLeod, ColinAC Munro LEOD, COLIN MUNRO (1909-1972) studied the use of sulfa drugs, synthetic substances that coun- Canadian-born American microbiologist teract bacteria, in treating pneumonia, as well as how Colin Munro MacLeod is recognized as one of the founders of Pneumococci develop a resistance to sulfa drugs. He also molecular biology for his research concerning the role of worked on a mysterious substance then known as “C-reactive deoxyribonucleic acid (DNA) in bacteria. Along with his col- protein,” which appeared in the blood of patients with acute leagues Oswald Avery and Maclyn McCarty, MacLeod con- infections. ducted experiments on bacterial transformation which MacLeod’s principal research interest at the Rockefeller indicated that DNA was the active agent in the genetic trans- Institute was the phenomenon known as bacterial transforma- formation of bacterial cells. His earlier research focused on the tion. First discovered by Frederick Griffith in 1928, this was a causes of pneumonia and the development of serums to treat phenomenon in which live bacteria assumed some of the char- it. MacLeod later became chairman of the department of acteristics of dead bacteria. Avery had been fascinated with microbiology at New York University; he also worked with a transformation for many years and believed that the phenom- number of government agencies and served as White House enon had broad implications for the science of biology. Thus, science advisor to President John F. Kennedy. he and his associates, including MacLeod, conducted studies MacLeod, the fourth of eight children, was born in Port to determine how the bacterial transformation worked in Hastings, in the Canadian province of Nova Scotia. He was the Pneumococcal cells. son of John Charles MacLeod, a Scottish Presbyterian minister, The researchers’ primary problem was determining the and Lillian Munro MacLeod, a schoolteacher. During his child- exact nature of the substance which would bring about a trans- hood, MacLeod moved with his family first to Saskatchewan formation. Previously, the transformation had been achieved and then to Quebec. A bright youth, he skipped several grades only sporadically in the laboratory, and scientists were not able in elementary school and graduated from St. Francis College, a to collect enough of the transforming substance to determine its secondary school in Richmond, Quebec, at the age of fifteen. exact chemical nature. MacLeod made two essential contribu- MacLeod was granted a scholarship to McGill University in tions to this project: He isolated a strain of Pneumococcus Montreal but was required to wait a year for admission because which could be consistently reproduced, and he developed an of his age; during that time he taught elementary school. After improved nutrient culture in which adequate quantities of the two years of undergraduate work in McGill’s premedical pro- transforming substance could be collected for study. gram, during which he became managing editor of the student By the time MacLeod left the Rockefeller Institute in newspaper and a member of the varsity ice hockey team, 1941, he and Avery suspected that the vital substance in these MacLeod entered the McGill University Medical School, transformations was DNA. A third scientist, Maclyn McCarty, receiving his medical degree in 1932. confirmed their hypothesis. In 1944, MacLeod, Avery, and Following a two-year internship at the Montreal McCarty published “Studies of the Chemical Nature of the General Hospital, MacLeod moved to New York City and Substance Inducing Transformation of Pneumococcal Types: became a research assistant at the Rockefeller Institute for Induction of Transformation by a Deoxyribonucleic Acid Medical Research. His research there, under the direction of Fraction Isolated from Pneumococcus Type III” in the Journal Oswald Avery, focused on pneumonia and the Pneumococcal of Experimental Medicine. The article proposed that DNA was infections which cause it. He examined the use of animal anti- the material which brought about genetic transformation. serums (liquid substances that contain proteins that guard Though the scientific community was slow to recognize the 359 • womi_M 5/7/03 7:52 AM Page 360 Magnetotactic bacteria WORLD OF MICROBIOLOGY AND IMMUNOLOGY • article’s significance, it was later hailed as the beginning of a ria can actively respond to their environment. Response to revolution that led to the formation of molecular biology as a light (phototaxis) and chemical concentration (chemotaxis) scientific discipline. exist in other species of bacteria. MacLeod married Elizabeth Randol in 1938; they even- The first magnetotactic bacterium, Aquasprilla magne- tually had one daughter. In 1941, MacLeod became a citizen totactum was discovered in 1975 by Richard Blakemore. This of the United States, and was appointed professor and chair- organism, which is now called Magnetospirillum magneto- man of the department of microbiology at the New York tacticum, inhabits swampy water, where because of the University School of Medicine, a position he held until 1956. decomposition of organic matter, the oxygen content in the At New York University he was instrumental in creating a water drops off sharply with increasing depth. The bacteria combined program in which research-oriented students could were shown to use the magnetic field to align themselves. By acquire both an M.D. and a Ph.D. In 1956, he became profes- this behavior, they were able to position themselves at the sor of research medicine at the Medical School of the region in the water where oxygen was almost depleted, the University of Pennsylvania. MacLeod returned to New York environment in which they grow best. For example, if the bac- University in 1960 as professor of medicine and remained in teria stray too far above or below the preferred zone of habi- that position until 1966. tation, they reverse their direction and swim back down or up From the time the United States entered World War II the lines of the magnetic field until they reach the preferred until the end of his life, MacLeod was a scientific advisor to oxygen concentration. The bacteria have flagella, which the federal government. In 1941, he became director of the enables them to actively move around in the water. Thus, the Commission on Pneumonia of the United States Army sensory system used to detect oxygen concentration is coordi- Epidemiological Board. Following the unification of the mili- nated with the movement of the flagella. tary services in 1949, he became president of the Armed Magnetic orientation is possible because the magnetic Forces Epidemiological Board and served in that post until North Pole points downward in the Northern Hemisphere. So, 1955. In the late 1950s, MacLeod helped establish the Health magnetotactic bacteria that are aligned to the fields are also Research Council for the City of New York and served as its pointing down. In the Northern Hemisphere, the bacteria chairman from 1960 to 1970. In 1963, President John F. would move into oxygen-depleted water by moving north Kennedy appointed him deputy director of the Office of along the field. In the Southern Hemisphere, the magnetic Science and Technology in the Executive Office of the North Pole points up and at an angle. So, in the Southern President; from this position he was responsible for many pro- Hemisphere, magnetotactic bacteria are south-seeking and gram and policy initiatives, most notably the United also point downward. At the equator, where the magnetic States/Japan Cooperative Program in the Medical Sciences. North Pole is not oriented up or down, magnetotactic bacteria In 1966, MacLeod became vice-president for Medical from both hemispheres can be found. Since the initial discovery in 1975, magnetotactic bac- Affairs of the Commonwealth Fund, a philanthropic organiza- teria have been found in freshwater and salt water, and in oxy- tion. He was honored by election to the National Academy of gen rich as well oxygen poor zones at depths ranging from the Sciences, the American Philosophical Society, and the near-surface to 2000 meters beneath the surface. American Academy of Arts and Sciences. MacLeod was en Magnetotactic bacteria can be spiral-shaped, rods and spheres. route from the United States to Dacca, Bangladesh, to visit a In general, the majority of magnetotactic bacteria discovered cholera laboratory when he died in his sleep in a hotel at the so far gather at the so-called oxic-anoxic transition zone; the London airport in 1972. In the Yearbook of the American zone above which the oxygen content is high and below which Philosophical Society, Maclyn McCarty wrote of MacLeod’s the oxygen content is essentially zero. influence on younger scientists, “His insistence on rigorous Magnetotaxis is possible because the bacteria contain principles in scientific research was not enforced by stern dis- magnetically responsive particles inside. These particles are cipline but was conveyed with such good nature and patience composed of an iron-rich compound called magnetite, or var- that it was simply part of the spirit of investigation in his lab- ious iron and sulfur containing compounds (ferrimagnetite oratory.” greigite, pyrrhotite, and pyrite). Typically, these compounds See also Bacteria and bacterial infection; Microbial genetics; are present as small spheres arranged in a single chain or sev- eral chains (the maximum found so far is five) in the cyto- Pneumonia, bacterial and viral plasm of each bacterium. The spheres are enclosed in a membrane. This structure is known as a magnetosome. Since many bacterial membranes selectively allow the movement of MAD COW DISEASE • see BSE AND CJD DISEASE molecules across them, magnetosome membranes may func- tion to create a unique environment within the bacterial cyto- plasm in which the magnetosome crystal can form.
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