MacLeod, Colin Munro (1909-1972) (World of Microbiology and Immunology)
Canadian-born American microbiologist
Colin Munro MacLeod is recognized as one of the founders of molecular biology for his research concerning the role of deoxyribonucleic acid (DNA) in bacteria. Along with his colleagues Oswald Avery and Maclyn McCarty, MacLeod conducted experiments on bacterial transformation which indicated that DNA was the active agent in the genetic transformation of bacterial cells. His earlier research focused on the causes of pneumonia and the development of serums to treat it. MacLeod later became chairman of the department of microbiology at New York University; he also worked with a number of government agencies and served as White House science advisor to President John F. Kennedy.
MacLeod, the fourth of eight children, was born in Port Hastings, in the Canadian province of Nova Scotia. He was the son of John Charles MacLeod, a Scottish Presbyterian minister, and Lillian Munro MacLeod, a schoolteacher. During his childhood, MacLeod moved with his family first to Saskatchewan and then to Quebec. A bright youth, he skipped several grades in elementary school and graduated from St. Francis College, a secondary school in Richmond, Quebec, at the age of fifteen. MacLeod was granted a scholarship to McGill University in Montreal but was required to wait a year for admission because of his age; during that time he taught elementary school. After two years of undergraduate work in McGill's premedical program, during which he became managing editor of the student newspaper and a member of the varsity ice hockey team, MacLeod entered the McGill University Medical School, receiving his medical degree in 1932.
Following a two-year internship at the Montreal General Hospital, MacLeod moved to New York City and became a research assistant at the Rockefeller Institute for Medical Research. His research there, under the direction of Oswald Avery, focused on pneumonia and the Pneumococcal infections which cause it. He examined the use of animal antiserums (liquid substances that contain proteins that guard against antigens) in the treatment of the disease. MacLeod also studied the use of sulfa drugs, synthetic substances that counteract bacteria, in treating pneumonia, as well as how Pneumococci develop a resistance to sulfa drugs. He also worked on a mysterious substance then known as "C-reactive protein," which appeared in the blood of patients with acute infections.
MacLeod's principal research interest at the Rockefeller Institute was the phenomenon known as bacterial transformation. First discovered by Frederick Griffith in 1928, this was a phenomenon in which live bacteria assumed some of the characteristics of dead bacteria. Avery had been fascinated with transformation for many years and believed that the phenomenon had broad implications for the science of biology. Thus, he and his associates, including MacLeod, conducted studies to determine how the bacterial transformation worked in Pneumococcal cells.
The researchers' primary problem was determining the exact nature of the substance which would bring about a transformation. Previously, the transformation had been achieved only sporadically in the laboratory, and scientists were not able to collect enough of the transforming substance to determine its exact chemical nature. MacLeod made two essential contributions to this project: He isolated a strain of Pneumococcus which could be consistently reproduced, and he developed an improved nutrient culture in which adequate quantities of the transforming substance could be collected for study.
By the time MacLeod left the Rockefeller Institute in 1941, he and Avery suspected that the vital substance in these transformations was DNA. A third scientist, Maclyn McCarty, confirmed their hypothesis. In 1944, MacLeod, Avery, and McCarty published "Studies of the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Deoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III" in the Journal of Experimental Medicine. The article proposed that DNA was the material which brought about genetic transformation. Though the scientific community was slow to recognize the article's significance, it was later hailed as the beginning of a revolution that led to the formation of molecular biology as a scientific discipline.
MacLeod married Elizabeth Randol in 1938; they eventually had one daughter. In 1941, MacLeod became a citizen of the United States, and was appointed professor and chairman of the department of microbiology at the New York University School of Medicine, a position he held until 1956. At New York University he was instrumental in creating a combined program in which research-oriented students could acquire both an M.D. and a Ph.D. In 1956, he became professor of research medicine at the Medical School of the University of Pennsylvania. MacLeod returned to New York University in 1960 as professor of medicine and remained in that position until 1966.
From the time the United States entered World War II until the end of his life, MacLeod was a scientific advisor to the federal government. In 1941, he became director of the Commission on Pneumonia of the United States Army Epidemiological Board. Following the unification of the military services in 1949, he became president of the Armed Forces Epidemiological Board and served in that post until 1955. In the late 1950s, MacLeod helped establish the Health Research Council for the City of New York and served as its chairman from 1960 to 1970. In 1963, President John F. Kennedy appointed him deputy director of the Office of Science and Technology in the Executive Office of the President; from this position he was responsible for many program and policy initiatives, most notably the United States/Japan Cooperative Program in the Medical Sciences.
In 1966, MacLeod became vice-president for Medical Affairs of the Commonwealth Fund, a philanthropic organization. He was honored by election to the National Academy of Sciences, the American Philosophical Society, and the American Academy of Arts and Sciences. MacLeod was en route from the United States to Dacca, Bangladesh, to visit a cholera laboratory when he died in his sleep in a hotel at the London airport in 1972. In the Yearbook of the American Philosophical Society, Maclyn McCarty wrote of MacLeod's influence on younger scientists, "His insistence on rigorous principles in scientific research was not enforced by stern discipline but was conveyed with such good nature and patience that it was simply part of the spirit of investigation in his laboratory."
See also Bacteria and bacterial infection; Microbial genetics; Pneumonia, bacterial and viral