Edward Lawrie Tatum (December 14, 1909 – November 5, 1975) was an American geneticist. He shared half of the Nobel Prize in Physiology or Medicine in 1958 with George Beadle for showing that genes control individual steps in metabolism. The other half of that year’s award went to Joshua Lederberg. Beadle and Tatum’s key experiments involved exposing the bread mold Neurospora crassa to x-rays, causing mutations. In a series of experiments, they showed that these mutations caused changes in specific enzymes involved in metabolic pathways. These experiments, published in 1941, led them to propose a direct link between genes and enzymatic reactions, known as the “one gene, one enzyme” hypothesis. Edward Tatum went on to study genetics in bacteria. An active area of research in his laboratory was to understand the basis of Tryptophan biosynthesis in Escherichia coli. Later, Tatum and his student Joshua Lederberg showed that E. coli could share genetic information through recombination. Edward Tatum was born in Boulder, Colorado. He attended college at the University of Chicago and received his PhD in biochemistry from the University of Wisconsin–Madison in 1934. Starting in 1937, he worked at Stanford University, where he began his collaboration with Beadle. He then moved to Yale University in 1945 where he mentored Lederberg. He returned to Stanford in 1948 and then joined the faculty of Rockefeller Institute in 1957. A heavy cigarette smoker, he died in New York City of heart failure complicated by chronic emphysema.