Oswald Theodore Avery
1877-1955
Canadian-American Bacteriologist and Physician
DNA's role in genetics and heredity was one of the focal points of biological inquiry in the second half of the twentieth century, but through most of the first half of the century there was little interest in this molecule. The person who changed all that was Oswald T. Avery. In 1944, he and his coworkers published evidence that DNA carried genetic information in bacteria, and this research first brought attention to this paper launched a renewed interest and research into DNA.
Avery was born in 1877 in Halifax, in the Canadian Province of Nova Scotia, and several years later, his family emigrated to the United States. Avery graduated from Colgate University in 1900 and then went to medical school at Columbia University College of Physicians and Surgeons in New York, graduating in 1904. After a brief period of medical practice and research at the Hoagland Laboratory in Brooklyn, Avery moved to the Rockefeller Institute for Medical Research in 1913. He spent the rest of his career there, retiring in 1948 to Tennessee, where he died in 1955.
At Rockefeller, almost all of Avery's research was on pneumococcus, the bacterium that causespneumonia, which at the turn of the century was a leading cause of death. By the time Avery was doing his work, several different types of pneumococcus had been identified. In 1917 Avery and Alphonse Dochez (1882-1964) found that these differences were due to substances on the surface of the bacteria, which also appeared in the blood of patients. Six years later, working with Michael Heidelberger (1888-1991), Avery identified these substances as polysaccharides, sugar molecules linked together. The different pneumococcus types produced polysaccharides with different combinations of sugars. A patient's immune system reacted against the bacteria's polysaccharides, which explained why immunity was specific for each pneumococcus type. This discovery was the first indication that the immune system could respond to polysaccharides; until this time it was assumed that only proteins could stimulate such a response.
In Britain, Fred Griffith (1877-1941) researched another difference among pneumococci strains: those with the polysaccharide coat formed large smooth colonies (the S form) when grown on agar gel, while those that lacked the coat formed rough-looking colonies and were incapable of causing infection (the R form). Griffith discovered that when live type II pneumococci of the R form were mixed with dead type I of the S form, and this mixture was injected into mice, the mice died of pneumonia, but of the type I kind. In other words, something—some chemical information—from the dead S-form bacteria had been transferred to the live R-form bacteria, allowing them to make the type I polysaccharide.
While Avery was skeptical of this result, biologists in his lab were able to reproduce it, and so he then set out to identify the substance responsible for the transformation of one type of pneumococcus bacterium into another. This effort began in 1928 and eventually involved the assistance of two collaborators, Colin MacLeod (1909-1972) and Maclyn McCarty (1911-). The results weren't published until 1944 because it proved difficult to achieve reproducible results. But finally they were able to show convincingly that what Avery called the "transforming factor" was DNA. Biologists long knew that DNA, along with protein, made up chromosomes, the cellular structures that appeared to carry genetic information. But the assumption had been that protein, with its 20 different building blocks, was the likely genetic material, and that DNA, with only 4 different building blocks, simply served as a structural foundation. Avery's workcalled this assumption into question, and while it took several years for his findings to be widely accepted, his research did spur others to at last look more closely at DNA. Among these researchers were James Watson (1928- ) and Francis Crick (1916- ), who worked out the structure of DNA in 1953. This discovery led to the tremendous level of interest in the molecular basis of genetics that characterized biology in the second half of the twentieth century.
Oswald T. Avery. (Library of Congress. Reproduced with permission.)This is the complete article, containing 669 words
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