Phage group
Encyclopedia
The phage group was an informal network of biologists centered around Max Delbrück
that contributed heavily to bacterial genetics
and the origins of molecular biology
in the mid-20th century. The phage group takes its name from bacteriophage
s, the bacteria-infecting virus
es that group used as experimental model organism
s. In addition to Delbrück, important scientists associated with the phage group include: Salvador Luria, Alfred Hershey
, Seymour Benzer
, Gunther Stent
, James D. Watson
, Frank Stahl, and Renato Dulbecco
.
had isolated and developed methods for detecting and culturing
them, beginning in 1917. Delbrück, a physicist-turned biologist seeking the simplest possible experimental system to probe the fundamental laws of life
, first encountered phage during a 1937 visit to T. H. Morgan's fly lab at Caltech. Delbrück was unimpressed with Morgan's experimentally complex model organism Drosophila
, but another researcher, Emory Ellis, was working with the more elementary phage. During the next few years, Ellis and Delbrück collaborated on methods of counting phage and tracking growth curve
s; they established the basic step-wise pattern of virus growth (the most obvious features of the lytic cycle
).
The phage group started around 1940, after Delbrück and Luria had met at a physics conference. Delbrück and Luria began a series of collaborative experiments on the patterns of infection for different strains of bacteria and bacteriophage. They soon established the "mutual exclusion principle" that an individual bacterium can only be infected by one strain of phage. In 1943, their "fluctuation test", later dubbed the Luria-Delbrück experiment
, showed that genetic mutations for antibiotic resistance
arise in the absence of selection
, rather than being a response to selection. That year, they also began working with Alfred Hershey
, another phage experimenter. (The three would share the 1969 Nobel Prize in Physiology or Medicine
, "for work on the replication mechanism and genetics of viruses".)
Delbrück, through his charm and enthusiasm, brought many biologists (and physicists) into phage research in the early 1940s. In 1944, Delbrück promoted the "Phage Treaty", a call for phage researchers to focus on a limited number of phage and bacterial strains, with standardized experimental conditions. This helped to make research from different laboratories more easily comparable and replicable, helping to unify the field of bacterial genetics
.
. Beginning in 1945, Delbrück and others taught young biologists the fundamentals of phage biology and experimentation, instilling the phage group's distinctive math- and physics-oriented approach to biology. Many of the leaders of the emerging field of molecular biology
were alumni of the phage course, which continued to be taught through the 1950s and 1960s.
Max Delbrück
Max Ludwig Henning Delbrück was a German-American biophysicist and Nobel laureate.-Biography:Delbrück was born in Berlin, German Empire...
that contributed heavily to bacterial genetics
Bacterial genetics
Bacterial genetics is the subfield of genetics devoted to the study of bacteria. Bacterial genetics are subtly different from eukaryotic genetics, however bacteria still serve as a good model for animal genetic studies. One of the major distinctions between bacterial and eukaryotic genetics stems...
and the origins of molecular biology
History of molecular biology
The history of molecular biology begins in the 1930s with the convergence of various, previously distinct biological disciplines: biochemistry, genetics, microbiology, and virology...
in the mid-20th century. The phage group takes its name from bacteriophage
Bacteriophage
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...
s, the bacteria-infecting virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es that group used as experimental model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
s. In addition to Delbrück, important scientists associated with the phage group include: Salvador Luria, Alfred Hershey
Alfred Hershey
Alfred Day Hershey was an American Nobel Prize-winning bacteriologist and geneticist.He was born in Owosso, Michigan and received his B.S. in chemistry at Michigan State University in 1930 and his Ph.D. in bacteriology in 1934, taking a position shortly thereafter at the Department of Bacteriology...
, Seymour Benzer
Seymour Benzer
Seymour Benzer was an American physicist, molecular biologist and behavioral geneticist. His career began during the molecular biology revolution of the 1950s, and he eventually rose to prominence in the fields of molecular and behavioral genetics. He led a productive genetics research lab both at...
, Gunther Stent
Gunther Stent
Gunther S. Stent was Graduate Professor of Molecular Biology at the University of California, Berkeley. He was born in Berlin as "Günter Siegmund Stensch"; the name was changed after the migration to the USA...
, James D. Watson
James D. Watson
James Dewey Watson is an American molecular biologist, geneticist, and zoologist, best known as one of the co-discoverers of the structure of DNA in 1953 with Francis Crick...
, Frank Stahl, and Renato Dulbecco
Renato Dulbecco
Renato Dulbecco is an Italian virologist who won a 1975 Nobel Prize in Physiology or Medicine for his work on reverse transcriptase. In 1973 he was awarded the Louisa Gross Horwitz Prize from Columbia University together with Theodore Puck and Harry Eagle. Dulbecco was the recipient of the Selman A...
.
Origins of the phage group
Bacteriophages had been a subject of experimental investigation since Felix d'HérelleFélix d'Herelle
Félix d'Herelle was a French-Canadian microbiologist, the co-discoverer of bacteriophages and experimented with the possibility of phage therapy.-Early years:...
had isolated and developed methods for detecting and culturing
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
them, beginning in 1917. Delbrück, a physicist-turned biologist seeking the simplest possible experimental system to probe the fundamental laws of life
Life
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...
, first encountered phage during a 1937 visit to T. H. Morgan's fly lab at Caltech. Delbrück was unimpressed with Morgan's experimentally complex model organism Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
, but another researcher, Emory Ellis, was working with the more elementary phage. During the next few years, Ellis and Delbrück collaborated on methods of counting phage and tracking growth curve
Growth curve
A growth curve is an empirical model of the evolution of a quantity over time. Growth curves are widely used in biology for quantities such as population size, body height or biomass...
s; they established the basic step-wise pattern of virus growth (the most obvious features of the lytic cycle
Lytic cycle
The lytic cycle is one of the two cycles of viral reproduction, the other being the lysogenic cycle. The lytic cycle is typically considered the main method of viral replication, since it results in the destruction of the infected cell...
).
The phage group started around 1940, after Delbrück and Luria had met at a physics conference. Delbrück and Luria began a series of collaborative experiments on the patterns of infection for different strains of bacteria and bacteriophage. They soon established the "mutual exclusion principle" that an individual bacterium can only be infected by one strain of phage. In 1943, their "fluctuation test", later dubbed the Luria-Delbrück experiment
Luria-Delbruck experiment
The Luria–Delbrück experiment demonstrates that in bacteria, genetic mutations arise in the absence of selection, rather than being a response to selection. Therefore, Darwin's theory of natural selection acting on random mutations applies to bacteria as well as to more complex organisms...
, showed that genetic mutations for antibiotic resistance
Antibiotic resistance
Antibiotic resistance is a type of drug resistance where a microorganism is able to survive exposure to an antibiotic. While a spontaneous or induced genetic mutation in bacteria may confer resistance to antimicrobial drugs, genes that confer resistance can be transferred between bacteria in a...
arise in the absence of selection
Selection
In the context of evolution, certain traits or alleles of genes segregating within a population may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively—meaning they contribute more offspring to the...
, rather than being a response to selection. That year, they also began working with Alfred Hershey
Alfred Hershey
Alfred Day Hershey was an American Nobel Prize-winning bacteriologist and geneticist.He was born in Owosso, Michigan and received his B.S. in chemistry at Michigan State University in 1930 and his Ph.D. in bacteriology in 1934, taking a position shortly thereafter at the Department of Bacteriology...
, another phage experimenter. (The three would share the 1969 Nobel Prize in Physiology or Medicine
Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will...
, "for work on the replication mechanism and genetics of viruses".)
Delbrück, through his charm and enthusiasm, brought many biologists (and physicists) into phage research in the early 1940s. In 1944, Delbrück promoted the "Phage Treaty", a call for phage researchers to focus on a limited number of phage and bacterial strains, with standardized experimental conditions. This helped to make research from different laboratories more easily comparable and replicable, helping to unify the field of bacterial genetics
Bacterial genetics
Bacterial genetics is the subfield of genetics devoted to the study of bacteria. Bacterial genetics are subtly different from eukaryotic genetics, however bacteria still serve as a good model for animal genetic studies. One of the major distinctions between bacterial and eukaryotic genetics stems...
.
Phage course at Cold Spring Harbor Laboratory
Apart from direct collaborations, the main legacy of the phage group resulted from the yearly summer phage course at Cold Spring Harbor LaboratoryCold Spring Harbor Laboratory
The Cold Spring Harbor Laboratory is a private, non-profit institution with research programs focusing on cancer, neurobiology, plant genetics, genomics and bioinformatics. The Laboratory has a broad educational mission, including the recently established Watson School of Biological Sciences. It...
. Beginning in 1945, Delbrück and others taught young biologists the fundamentals of phage biology and experimentation, instilling the phage group's distinctive math- and physics-oriented approach to biology. Many of the leaders of the emerging field of molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...
were alumni of the phage course, which continued to be taught through the 1950s and 1960s.