Max Delbruck Nobel Prize in Physiology or Medicine, 1969, jointly with Alfred Hershey and Salvador Luria Date of Birth: 04.09.1906 Country: USA

1. Biography of Max Delbrück
2. Early Education and Career
3. Research on Bacteriophages
4. Contributions to Genetics and Molecular Biology
5. Research on Genetic Recombination
6. Nobel Prize and Later Years

Biography of Max Delbrück

Max Ludwig Henning Delbrück, a German-American molecular biologist, was born in Berlin and was the youngest of seven children. His father, Hans Delbrück, was a professor of history at the University of Berlin and the publisher of the journal "German Yearbook". His mother, Lina (Twerch) Delbrück, was the daughter of a professor of surgery in Leipzig and the granddaughter of chemist Justus von Liebig. Growing up in a middle-class environment in the suburb of Grunewald, Delbrück showed early interest in mathematics and astronomy.

Early Education and Career

After graduating from the Grunewald Gymnasium in 1924, Delbrück enrolled at the University of Tübingen to study astronomy. However, after the first semester, he transferred to the University of Berlin, where he was exempt from tuition fees because his father was a faculty member. He then moved to the University of Bonn, returned to the University of Berlin, and eventually settled at the University of Göttingen, where he studied for three years.

In Göttingen, Delbrück began writing a dissertation on the formation of new stars. However, due to his inability to read literature in English and his lack of knowledge in the mathematical aspects of astrophysical theory, he abandoned the dissertation. During his time in Göttingen, Delbrück met E.R. Wigner and Max Born, who were working at the university faculty. Utilizing one of Born's theorems as the basis for his dissertation, Delbrück developed mathematical proofs of lithium chemical bonding, which earned him a doctorate in physics in 1930.

A Rockefeller Foundation fellowship allowed Delbrück to conduct research at the University of Bristol in England for a year and a half. There, he worked alongside Cecil F. Powell and befriended P.M.S. Blackett, P.A.M. Dirac, and other scientists who made significant contributions to the development of 20th-century physics. Delbrück's work in Bristol, largely theoretical, included two articles on quantum mechanics.

After Bristol, Delbrück spent six months working at the University of Copenhagen under the guidance of Niels Bohr, and the following six months at the University of Zurich under the guidance of Wolfgang Pauli. In Copenhagen, Delbrück formed friendships not only with Bohr but also with physicists George Gamow and Victor Weisskopf. Bohr's theory of complementarity significantly changed Delbrück's views on biology and genetics. According to the concept of complementarity, wave and quantum theories express different aspects of electromagnetic interaction and therefore, different aspects of physical reality. Bohr's assumption that this physical phenomenon would also be found in biological phenomena greatly influenced Delbrück's further research.

Research on Bacteriophages

After returning to Berlin in 1932, Delbrück began working as an assistant to Lise Meitner, who, along with Otto Hahn, was studying the effects of uranium radiation on neutron emission. During this time, Delbrück frequently met with physicists and biologists interested in genetic problems. Shortly before this, Hermann Muller had demonstrated that ionizing radiation causes genetic mutations. This confirmed the Berlin researchers' belief that "genes have the same stability as molecules of a chemical nature." In the mid-1930s, genes were "used as algebraic units in complex genetic research and identified with molecules analyzed using the terminology of structural chemistry." In his well-known work written in 1937, Delbrück proposed considering genes as molecules and "viral replication as a special form of primitive gene replication." "Such a viewpoint," he said, "significantly simplifies the question of the origin of many extremely complex and specific molecules found in every organism... and necessary for the simplest metabolic exchanges."

In 1937, Delbrück received a second Rockefeller Foundation fellowship, which he used to study biology and genetics at the California Institute of Technology (Caltech) in Pasadena. There, he worked with Thomas Hunt Morgan, studying the genetics of the fruit fly (Drosophila melanogaster), a widely used organism in genetic research due to its short lifespan and abundant offspring. While Morgan and other geneticists studied Drosophila to understand the state of chromosomes and their changes, Delbrück became interested in the genetics of bacteriophages, a type of virus that infects bacterial cells. Bacteriophages, like all viruses, are the simplest form of life and consist of nucleic acid located in the center and an outer protein coat. At present, three possible outcomes of bacteriophage penetration into a bacterial cell are known. It can affect the cell's biochemical apparatus, replication, and cause cell lysis, releasing new phage particles. On the other hand, a bacteriophage can integrate into the DNA of a bacterial cell; in this case, the resulting prophage is transmitted to descendant cells during cell division, similar to a bacterial gene. If the prophage is activated (e.g., by ultraviolet radiation), it can behave again as an autonomous bacteriophage and cause lysis of the bacterial cell. The third possibility is the degradation of the bacteriophage by bacterial cell enzymes. Delbrück and biologist Emory Ellis developed experimental methods for studying bacteriophages, as well as a mathematical system for analyzing the results of their experiments. In their first work, written in 1939, they examined the single-cycle reproduction of phages in individual cells, laying the foundation for a new era of virus research.

Contributions to Genetics and Molecular Biology

When World War II began, Delbrück remained in the United States. He accepted a position as a physics professor at Vanderbilt University in Nashville, Tennessee, where he continued his bacteriophage research for the next seven years.

In 1940, at a meeting of the American Physiological Society in Philadelphia, Delbrück met Salvador Luria, who was conducting bacteriophage research at the College of Physicians and Surgeons of Columbia University in New York. Finding common interests in their research, Delbrück and Luria began discussing the results of their experiments through correspondence and occasional meetings. Their findings indicated that the DNA of a bacterial cell undergoes spontaneous mutations, affecting the cell's immunity or, in other words, its resistance to bacteriophage lysis. These observations, published in 1943, became a model for analyzing and generalizing the results of experimental genetic research. Presenting the first evidence of bacterial heredity through genes, their article refuted the prevailing belief in the acquisition of genetic traits and marked the beginning of the era of bacterial genetics and molecular biology.

In 1943, Delbrück began collaborating on bacteriophage research with Alfred Hershey, a microbiologist from the University of Washington. Hershey, Delbrück, and Luria formed a group to study phages, devising a plan for their research. Through informal meetings with other researchers, the group directed their work towards studying seven bacteriophages that infect the Escherichia coli B line, a common organism in genetic research. Two years later, Delbrück organized the first bacteriophage research courses at Cold Spring Harbor Laboratory in New York. These courses, which covered quantitative and statistical methods of research, were held every summer until 1971 and attracted biologists, geneticists, and physicists from around the world.

In 1947, Delbrück was appointed as a professor of biology at Caltech and was elected to the National Academy of Sciences two years later.

Research on Genetic Recombination

Working independently from each other, Delbrück and Hershey discovered in 1946 the possibility of genetic information (genes) exchange between two different lines of bacteriophages when the same bacterial cell is infected with multiple phages. This phenomenon, which they called genetic recombination, was the first experimental evidence of DNA recombination in viruses. Later, in 1952, Hershey and his colleague Martha Chase confirmed that genes are made of DNA. The following year, Francis Crick and James D. Watson determined the three-dimensional structure of DNA; Watson shared the first data on the double helical structure of DNA in a letter to Delbrück. In the 1950s and 1960s, Delbrück's laboratory became a meeting place for many researchers, including Watson and Francois Jacob, discussing experimental designs, problems of solving the genetic code, and other current issues in genetic research.

Nobel Prize and Later Years

Delbrück, Hershey, and Luria shared the Nobel Prize in Physiology or Medicine in 1969 "for their discoveries concerning the replication mechanism and the genetic structure of viruses." "The main credit belongs to Delbrück, who transformed bacteriophage research from a field of wandering empiricism to an exact science," said Sven Gard of the Karolinska Institute during the award presentation. "He analyzed and formulated conditions for the precise measurement of biological effects. Together with Luria, he carefully developed quantitative methods and established statistical criteria for evaluation, enabling further in-depth research."

After World War II, Delbrück received invitations to work at various institutes, and in late 1946, he was appointed as the head of biological research at Caltech upon the invitation of George W. Beadle. Starting in 1947, he remained there until his retirement in 1977 when he was elected to the Board of Trustees of the institute. In his later years, Delbrück became interested in the molecular biology of sensory perception and studied Phycomyces, a simple light-responsive fungus that moves towards light. During a self-funded sabbatical from 1961 to 1963, he worked as a visiting professor at the University of Cologne in West Germany, assisting in the establishment of the Institute of Genetics at the university.

In 1941, Delbrück married Marie Adeline Bruce, whom he met at Caltech. They had four children together. Delbrück's students and colleagues valued not only his organizational abilities but also his wit and disregard for social conventions. He would sometimes host parties, asking some guests to dress formally and others to come in tennis attire, while he himself would appear in different styles of clothing. Delbrück had a great interest in philosophy, music, and literature and was deeply saddened by his inability to attend a lecture on German poet Rainer Maria Rilke at the Poetry Center in New York due to illness. In 1978, Delbrück was diagnosed with a malignant bone marrow tumor, which, along with the side effects of chemotherapy, limited his activity. He passed away on March 10, 1981, in Pasadena.

Delbrück's awards and honors include honorary degrees from the University of Copenhagen, University of Chicago, Heidelberg University, Harvard University, and the University of Göttingen, as well as Gustavus Adolphus College and the University of Southern California. He received the Kimber Genetics Award from the National Academy of Sciences (1964), the Gregor Mendel Medal from the German Academy of Sciences Leopoldina (1967), and the Louise Gross-Horwitz Prize from Columbia University (1969). Delbrück was a member of the National Academy of Sciences, the American Academy of Arts and Sciences, the Royal Danish Academy, the Royal Society of London, and the French Academy of Sciences.