Oswald Avery, Colin MacLeod and Maclyn McCarty conducted an experiment in 1944 that demonstrated that DNA is the substance that causes bacterial transformation and explained the ‘transforming principle’ observed in Griffith’s 1928 experiment.
Avery was born in Halifax, Nova Scotia and his parents were strong and enterprising people; MacLeod was born in Glace Bay, Nova Scotia and received his B.A. from St. Francis Xavier University; McCarty was born in South Bend, Indiana and received his B.S. from Stanford University in 1933 and his M.D. from Johns Hopkins University School of Medicine in 1937.
Avery worked at the Rockefeller Institute for Medical Research from 1913 onward while Colin MacLeod was a researcher and lecturer in bacteriology and immunology in the Brooklyn borough of New York City at the Hoagland Laboratory. Maclyn McCarty also worked at the Rockefeller Institute for Medical Research where the experiment was conducted and their full study was published in the Journal of Experimental Medicine in 1944.
Oswald Avery
Colin MacLeod
Maclyn McCarty (with Watson and Crick)
Oswald Avery, Colin MacLeod and Maclyn McCarty conducted an experiment in 1944 that demonstrated that DNA is the substance that causes bacterial transformation, at the Rockefeller Institute for Medical Research.
The experiment was conducted on Streptococcus pneumoniae bacteria which can cause pneumonia.
The experiment was conducted in two parts.
In the first part, they grew two strains of bacteria: one strain was pathogenic (disease-causing) and had a smooth appearance (S strain), while the other strain was non-pathogenic and had a rough appearance (R strain). They then killed the S strain bacteria with heat and mixed them with live R strain bacteria.
In the second part of the experiment, they extracted various cellular components from the heat-killed S strain bacteria and added them to live R strain bacteria.
The results of their first investigation showed that the R strain bacteria had been transformed into S strain bacteria.
In the second part they found that only DNA extracted from the S strain bacteria could transform R strain bacteria into S strain bacteria.
This experiment was significant because it showed that DNA is responsible for bacterial transformation and therefore is likely to be the genetic material of bacteria.