What can a slot machine teach a scientist about mutations in bacteria? Quite a lot, if the scientist is Salvador E. Luria (1912–1991). He is the latest scientist to be added to the Profiles in Science Web site, created by the National Library of Medicine, a part of the National Institutes of Health in Bethesda, Maryland.

Early in 1943, Salvador Luria, an Italian-born bacteriologist was trying to determine how bacteria become resistant to specific viruses following infection: was the mutation to a resistant form provoked by exposure to the virus? Or was it spontaneous and random? The answer struck him one evening as he watched a friend playing a slot machine.

Bacterial mutations, Luria realized, might occur in a pattern analogous to payouts from the slots: slot machines return about 90 percent of money put into them, but distributed very unevenly — most trials produce nothing, some yield very small amounts, and a few yield jackpots. If random mutation was occurring in 20 different bacteria cultures exposed to a virus, there would be resistant colonies in some of the cultures, none in others, and very large ones in a few. This is exactly what Luria found.

The discovery, made with Max Delbrück (who worked up a mathematical proof that calculated mutation rates from the number of mutants observed), marked the birth of bacterial genetics and demonstrated the utility of bacteria for genetics research. Luria shared the 1969 Nobel Prize in Physiology or Medicine with Max Delbrück and Alfred Hershey for their “discoveries concerning the replication mechanism and the genetic structure of viruses.”

Profiles in Science has digitized and made available over the World Wide Web a selection of the papers of Salvador Luria for use by educators, researchers, and the public. The papers selected for digitization are from the Luria materials in the American Philosophical Society. This brings to 16 the number of notable researchers and public health officials whose personal and professional records are featured on the “Profiles in Science” site at http://www.profiles.nlm.nih.gov.

“Luria’s work with Max Delbrück brought bacterial viruses to the center stage of genetics research in the 1940s, and he helped develop bacterial genetics into one of the roots of molecular biology as we know it today,” said Donald A.B. Lindberg, M.D., director of the National Library of Medicine.

Born in Turin, Italy, on August 13, 1912, Luria graduated from the University of Turin Medical School in 1935. He sought training in radiation biology, and encountered Max Delbrück’s recent theories about the gene as a molecule. Soon afterwards, Luria was introduced to bacteriophages — viruses that infect bacteria.

By 1938, Luria, as a Jew, was barred from academic research fellowships in Italy as that nation increasingly aligned itself with Nazi Germany. He moved to Paris to continue his work. When the German army invaded in 1940, Luria fled to the United States, where he finally met Max Delbrück. Recognizing their common research interests, they planned experiments to conduct over the summer of 1941 at Cold Spring Harbor Laboratory on Long Island.

In 1943, Luria, inspired by the slot-machine analogy, demonstrated that bacteria mutated spontaneously into phage-resistant forms. Delbrück and he then developed the “fluctuation test” for calculating bacterial mutation rates. This work provided statistical evidence for the existence of genes in bacteria, and thus established microbes as suitable subjects for genetics research.

During the 1940s, Luria continued his investigations into bacteriophage and taught and mentored at Indiana University. (His first graduate student was James Watson, who went on to discover the structure of DNA with Francis Crick.)

In 1959, Luria joined the faculty at the Massachusetts Institute of Technology as the chair of its new microbiology program. There his research focus shifted to questions about cell membranes, and enzymes within them.

Although he was not involved in resistance activities in Italy or France during the 1930s and 1940s, Luria was almost always politically engaged at some level after moving to the United States. He joined biochemist Linus Pauling and many others in protesting nuclear weapons testing during the 1950s and the building of new atomic power plants in the 1970s. He was also an active participant in the peace movement and was an outspoken critic of American intervention in Vietnam.

The online exhibit features correspondence, published and unpublished articles and monographs, photographs, lectures, speeches, and laboratory notebooks from Luria’s files. An introductory exhibit section places Luria’s achievements in historical context.

Profiles in Science was launched September 1998 by the National Library of Medicine. The Library, the world’s largest library of the health sciences, is a component of the National Institutes of Health, U.S. Department of Health and Human Services.

The National Institutes of Health (NIH) — The Nation's Medical Research Agency — includes 27 Institutes and Centers and is a component of the U. S. Department of Health and Human Services. It is the primary Federal agency for conducting and supporting basic, clinical, and translational medical research, and investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit http://www.nih.gov.