An Interview with Manuel F. Varela and Ann F. Varela: Edward Tatum, Metabolism-Controlling Genes, Mold Mutants, and the Nobel Prize

Feb 8, 2021 by

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Edward Tatum

The concepts of biochemical genetics have already been, and will undoubtedly continue to be, significant in broader areas of biology.”

― Edward Tatum

In microbiology, the roles of mutation and selection in evolution are coming to be better understood through the use of bacterial cultures of mutant strains.”

― Edward Tatum

Michael F. Shaughnessy

1) Edward Tatum—where was he born, when was he born, and where did he go to school?

A Nobel Laureate and Professor, Edward L. Tatum is world-renowned for his work dealing with the idea that genes control the metabolism of living organisms. Edward Lawrie Tatum was born in Boulder, Colorado, on December 14, 1909. His twin died soon after birth. He was one of three children of Arthur Lawrie Tatum, an eminent pharmacologist, and Mabel Webb Tatum, one of the University of Colorado’s first female graduates. Tatum’s father was on the University of Chicago faculty until 1928. He relocated to the University of Wisconsin Medical School to accept a Pharmacology Professor position.

For two years, Tatum attended the University of Chicago and then transferred to the University of Wisconsin at Madison, earning his B.A. degree in Chemistry in 1931. He earned his M.S. degree in Microbiology in 1932 and his Ph.D. degree in Biochemistry in 1934 at Madison.

2) Tatum’s doctoral work—what was his dissertation all about at Wisconsin?

Edward Tatum’s thesis involved researching the nutritional needs and metabolism of specific microbes. His early work involved an analysis of factors that stimulated the growth of various fermenting bacteria. Tatum worked with Harland Goff Wood and was supervised by William Harold Peterson and Edwin Broun Fred. They mixed different bacterial species and examined their abilities to produce fermentation products. For instance, they found that the acetone-butyl alcohol bacterium of the genus Clostridium and lactic acid bacterium of the genus Lactobacillus worked together to undergo lactic acid production. He studied propionic acid bacteria species of the genus Propionibacterium. They examined the metabolism of amino acids like aspartic acid and asparagine in these bacteria.

One of Tatum’s important discoveries involved the need for vitamin B1, thiamine, as one of the vital growth factors for microorganisms. See Figure 89. Tatum worked with H.G. Wood and W.H. Peterson. They examined a growth-stimulant in yeast extract, egg albumin, milk, and a milk protein hydrolysate, called caseinogen. The growth-stimulant worked better when combined with amino acids but could not be replaced with vitamin B5, vitamin C, or niacin and other known growth-enhancing substances. However, their new growth substance was purified and shown to be identical to thiamine, known as vitamin B1. Tatum and colleagues showed that a substance known to be essential in animals and humans was also a necessary growth factor in microbes such as the propionic acid bacteria.

File:Thiamine cation 3D ball.png

Figure 89. Molecular model of thiamine, also known as vitamin B1, an essential nutrient.

In humans, vitamin B1 is neither produced nor even stored anywhere in the body. Thus, humans must acquire the molecule in the diet. A deficiency in dietary vitamin B1 can result in pathological conditions known as beriberi and Wernicke-Korsakoff syndrome. Beriberi can be lethal. It involves neuropathological conditions manifested by pain, inability to contract muscles, tissue wasting, and swelling. Historically, beriberi has been noted in populations that process rice (milling) in such a manner as to eliminate vitamin B1. Once the problem became known, alterations in the rice processing practices reduced the incidences. In modern times, beriberi still exists in chronic cases of alcoholism and in world regions that experience famine.

The Wernicke-Korsakoff syndrome is another life-threatening illness that is due to a vitamin B1 deficiency. The syndrome has several causes, such as acute and chronic alcoholism, poor-quality diet, and secondary conditions that impair vitamin B1 absorption in the gastrointestinal tract. A patient with Wernicke-Korsakoff syndrome can experience unsteadiness, eye problems, memory loss, and confusion reminiscent of dementia.

3) Tatum worked with Joshua Lederberg —what was the result of their collaboration?

In 1946, Tatum served as a scientific mentor to Joshua Lederberg at Yale. During this time, Lederberg was a medical student who was interested in research in the laboratory. Together with Lederberg, Tatum broadened the studies of nutritional mutants with the Escherichia coli bacterial strain K12. Tatum and Lederberg plated their Escherichia coli in three layers on minimal agar medium plates. They incubated the plates, permitting the bacteria to form tiny colonies. Next, they added a new layer of nutrient agar, containing new growth factors, and allowed the colonies to grow larger.

Mutants of Escherichia coli were detectable by their failure to grow into full-sized colonies. Sometimes their sustained isolation of these sorts of mutants was unstable. They would revert to the wild-type form, which was an undesirable result. They needed more Escherichia coli mutants. Thus, Tatum and Lederberg tried various mutant-inducing methods, such as chemicals that targeted DNA, X-rays, and UV light beams. The new mutagenesis treatments facilitated the production of Escherichia coli mutants.

Hence, Tatum and Lederberg purified a collection of Escherichia coli variants that were defective in producing amino acids and vitamins. The amino acids that their mutants could not make included proline, histidine, methionine, and cystine. Vitamins that their Escherichia coli mutants were unable to produce contained p-aminobenzoic acid and thiamine. Tatum and Lederberg published the work together in 1946 in the Journal of Biological Chemistry.

A different research project conducted by Tatum and Lederberg at Yale involved bacterial conjugation and gene recombination. In their experiment, they mixed distinct mutants in the same culture vessels. Each Escherichia coli mutant was defective in producing different but necessary growth factors. One of these mutants could not grow without supplemental thiamine, threonine (an amino acid), and leucine (another amino acid). This so-called Escherichia coli triple mutant was mixed with another defective in making cysteine, phenylalanine, both of which are amino acids, and biotin, which is known as vitamin B7. When cultured separately, they could not grow unless their essential nutrients were supplied in their growth media.

However, shockingly, Tatum and Lederberg found that when the triple mutants were mixed, several brand-new bacterial variants emerged in which no nutrient supplementation was needed! The mixing of the two defective mutants produced normal Escherichia coli bacteria!

Tatum and Lederberg reasoned that the genes from each of the defective mutants supplied their regular gene versions. The mutated genes recombined with the other’s corresponding wild-type genes to produce a normal-working wild-type Escherichia coli cell. That is, the bacterial genes are assorted with each other to form new gene combinations. The process is known today as gene recombination. In their paper, published in the journal Nature in October of 1946, Tatum and Lederberg concluded that bacteria were undergoing sexual reproduction and recombining their DNA in the meantime.

Lederberg and Tatum conducted an extensive follow-up study. They evaluated the metabolism-defective Escherichia coli mutants and their relationship to bacteriophage infection. Normal unmutated Escherichia coli cells (wild-type or parental) were called prototrophs. However, Escherichia coli mutants that were deficient in producing a nutrient and needing a nutritional supplementation to live were called auxotrophs. In their auxotrophic Escherichia coli repertoire, Lederberg and Tatum had so-called single-, double- and triple-mutants, each with various defects in their nutritional statuses. Lederberg and Tatum also measured these Escherichia coli auxotroph mutants’ ability to resist infection by the so-called “T phages,” which were numbered T1 through T7. They tested whether the prototrophs and auxotrophs were susceptible or resistant to these phages.

The method was simple. Lederberg and Tatum merely cross-streaked phage solutions with bacteria on a nutrient agar plate. They then examined the intersections for lysis of the bacteria. If the crossings showed lysis, the bacteria were phage susceptible. Likewise, if the cross streaks showed no lysis at the intersections, then it meant that the bacteria were resistant. Perhaps no longer surprised at this point, Lederberg and Tatum found that genes encoding metabolism-conferring properties could also recombine with those that specified phage resistance. Lederberg and Tatum had definitive evidence demonstrating that genetic recombination was possible during conjugation (bacterial sex) and transduction (viral infection). It was a significant discovery. The intriguing results shocked the world after Lederberg and Tatum published the Journal of Bacteriology findings in June of 1947.

4) In 1937—Stanford University and George Beadle—What was going on during those years?

Before Tatum arrived at Stanford, he spent a year in the Netherlands at the University of Utrecht after his Ph.D. continuing research on milk’s bacterial strains. In 1937, he entered the dairy industry and conducted butter research; however, Tatum applied for and secured a research associate position in George Beadle’s lab at Stanford University.

Tatum’s microbiology and biochemistry abilities would be a boon to the lab; Beadle’s contribution was his impressive genetics knowledge. There he would have an excellent research opportunity working with Drosophila. For the first few years, Tatum worked on isolating and identifying the “substances” involved in Drosophila eye color determination. Unfortunately, their efforts did not result in being the first research team to get the biochemical details on those “substances.” In 1940, Tatum recognized a fortuitous opportunity with this research disappointment. His new project involved a fungus called Neurospora. He and Beadle would collaborate and ultimately significantly affect the future of genetics.

They used X-rays to produce mutant strains of the pink bread mold Neurospora crassa. They studied the spores’ sexual reproduction, isolating a spore that would grow only when given vitamin B6 (pyridoxine). Tatum and Beadle concluded that an X-ray-damaged gene was responsible for the spore’s inability to produce the enzyme necessary for vitamin B6 production. Tatum discovered that biotin was required to cultivate this fungus on simple inorganic media successfully. These findings provided these two workers with the genetic material that they needed for the work that gained them, together with Joshua Lederberg, the Nobel Prize.

This research was the first affirmation of what would later be known as the “one gene, one enzyme” theory. It was revealed in the Proceedings of the National Academy of Sciences in 1941, the same year that Tatum was promoted to assistant professor at Stanford. By the end of World War II, the team of Beadle and Tatum had attained global notoriety.

5) Tatum did win the Nobel Prize— for what was this accolade to Tatum bequeathed? 

Indeed, Tatum shared half of the Nobel Prize in physiology or medicine in 1958 with George Beadle (Chapter 2). They each took a quarter of the award. Joshua Lederberg (Chapter 10) garnered the other half of this Nobel Prize. Tatum and Beadle’s astonishing discovery had been that they demonstrated the specific genes regulated distinct metabolic steps in the bread mold Neurospora crassa. The discovery came to be affectionately known as the so-called “one gene encodes one enzyme” hypothesis. Lederberg’s great find had been that he demonstrated bacteria underwent sexual mating and exchange of genetic material.

The path to the Nobel for Tatum and Beadle had been vexed by a rough start. Near the late 1930s and early 1940s, Tatum was a postdoctoral fellow supervised by Beadle at Stanford University. Initially, they had been studying fruit fly genetics. Their goal had been to identify and isolate the substance responsible for determining vermilion eye color. Morgan’s famous fruit fly mutants with no eye color had inspired Tatum and Beadle. Unfortunately, their project with Drosophila failed.

Unbeknown to Beadle and Tatum, their first isolation of the eye color determining substance had been a bacterial contaminant that had supplied the active substance. More problems occurred when Tatum attempted to isolate the eye color substance from the contaminant bacterium, a member of the genus called Bacillus. Tatum isolated from the contaminating bacteria a biochemical that was itself contaminated with another substance! The eye color substance was supposed to be chemical kynurenine. Tatum had, instead, purified a complex between kynurenine and sucrose! At the time, the problem of refining the eye color substance from fruit flies had become a sweetened mess.

In modern times, we know that the correct gene for the eye color vermilion encodes an enzyme that alters the amino acid tryptophan to N-formyl-kynurenine. The N-formyl-kynurenine, in turn, is changed into kynurenine by yet another enzyme. To complicate matters, the gene for the cinnabar eye color encodes an enzyme that converts kynurenine to 3-hydroxy-kynurenine. In the colorless eye mutants, these genes are missing. Eye color in the fruit fly was a complicated genetic and biochemical scheme.

When Adolf Butenandt and collaborator Alfred Kuhn had beaten everyone in the quest to solve the cinnabar and vermilion eye color puzzle, Tatum and Beadle abandoned the project. While dismayed at the time by their failure, they switched their research paradigm to Neurospora fungi. The switch would prove astonishingly fortuitous for Beadle and Tatum.

They began their new line of investigation from scratch. First, Tatum and Beadle identified the nutritional requirements of the Neurospora crassa. Within days, they discovered that biotin was the only essential substance. It was a fortunate property.

Next, Tatum and Beadle exposed the Neurospora fungi cultures to radiation, generating a collection of mutants for nutritional-requirement studies. In one grand experiment, they had purified several thousand mutants! Tatum and Beadle measured the mutants’ growth requirements on various culture media. They found Neurospora mutants that grew well on regular culture media supplied with amino acids and vitamins but could not grow on minimal media that lacked these supplements. Tatum and Beadle reasoned that such mutants were defective in the biochemical pathways that made the amino acids and vitamins.

Then, with their Neurospora mutant collections in hand, Tatum and Beadle permitted each of their mutants to mate with non-mutagenized wild-type Neurospora crassa. The progeny that failed to grow on minimal media without any one of the amino acids and vitamins were of interest. These growth properties could help identify which nutrients the Neurospora mutants were defective in producing themselves.

Tatum and Beadle tested each of the progeny mutants for their nutrient requirements. They placed their mated mutants in minimal culture media, each flask supplied with one nutrient. In particular, one Neurospora mutant, called number 299, grew well in a minimal medium supplied with pyridoxine, also known as vitamin B6. Soon, they found a variety of mutants in which each clone had lost one nutrient-producing step. Tatum and Beadle would interpret these findings with Neurospora auxotroph mutants as having affected a single gene per nutrient requirement. That is, each gene was concerned with controlling a single biochemical reaction. The massive project was published in a series of papers in the 1940s. These investigations would earn Tatum and Beadle the Nobel Prize.

6) Tatum taught at Yale—what exactly did he teach—and how long was he there?

Tatum left Stanford in 1945 to accept a position as associate professor of biology at Yale University; he was to advance the microbiology program. He continued studies on the effect of biochemical mutations on nutritional deficiencies of the bacterium Escherichia coli. He was promoted to professor of microbiology the following year.

At Yale, Tatum had recruited Joshua Lederberg. The latter was interested in the Neurospora mutant studies. Tatum and Beadle showed that mating with wild-type parental fungi was an essential step in discovering that one gene controlled a single metabolic action. Lederberg was interested in doing similar types of study with bacteria. The problem, however, was that at the time, it was not entirely clear that bacterial mutants could be mated with wild-type counterparts. As related above, Tatum and Lederberg discovered that bacteria like Escherichia coli not only participated in sexual mating, but genetic material was also exchanged and recombined in the process. This work would come to the attention of Jim Watson. In later years, he would write about the discovery in his classic memoir, “The Double Helix,” and its sequels.

Tatum left Yale in 1948 to return to Stanford, wherein 1956 he was appointed head of a new department of biochemistry. Sometime after his marriage to June Alton was at an end, he moved to New York City and married Viola Kanter. In 1957, Tatum became a professor at the Rockefeller Institute of Medical Research (now Rockefeller University). He continued his studies on how genes determine the characteristics of living organisms.

7) Biotin—it seemed to figure heavily in Tatum’s work—why is this chemical so important?

As we mentioned above, biotin is also called vitamin B7. See Figure 90. Tatum’s work involved studying with Lederberg mutants of bacteria and with Beadle mutants of fungi that were defective in making biotin. Although rare in modern times, a deficiency in human dietary biotin produces symptoms such as a rash near the eyebrows, pain in the muscles, and extreme tiredness.

Amongst the biochemists, biotin is well known as an essential co-factor to the enzyme called pyruvate carboxylase. As such, biotin serves as an “activated carrier” of carbon dioxide. Biotin can combine with the amino acid called lysine to form an adduct called biocytin. The biocytin participates in ATP-dependent biochemical reactions that attach carbon dioxide to various substances.

File:Biotin 3d model1.png

Figure 90. The three-dimensional model of biotin.

Biochemically, biotin serves as an essential co-factor for the enzyme called pyruvate carboxylase. The enzymatic process involves converting pyruvate, a central metabolite, to oxaloacetate, a critical intermediate for the Krebs cycle. The pyruvate carboxylase enzyme uses ATP hydrolysis as an energetic driving force. Bicarbonate functions as a source of carbon dioxide for attachment. Biotin is attached to lysine as it acts as an activated carrier of the needed carbon dioxide.

Biotin plays a role in the body’s fat metabolism. A significant biochemical role for biotin involves its participation in the fatty acid breakdown by its oxidation in the body. The fatty acid breakdown product propionyl CoA is converted to D-methylmalonyl CoA by the enzyme called propionyl CoA carboxylase, which requires biotin. The fatty breakdown pathway entails producing succinyl CoA. Interestingly, the reaction requires another co-factor called vitamin B12 (cobalamin).

Biotin is required in the biochemical steps that make fatty acids. One of these uses acetyl CoA carboxylase 1, an enzyme that converts acetyl CoA to malonyl CoA. The biochemistry step involves another biotin with its activated carbon dioxide and ATP hydrolysis. This particular biochemical reaction targets the growth of cancerous cells, especially in cases of breast and prostate cancers.

In modern times, biotin can be attached to another biochemical called avidin, a protein found abundantly in egg white. The biotin-avidin complex is then used to inhibit biotin-requiring biochemical reactions. Biotin has also been used as a marker to study protein chemistry.

8) Sadly, Tatum was a heavy cigarette smoker and died relatively young—what was the causal factor in his death?

It has been reported that Tatum was a heavy smoker and suffered from chronic emphysema. On November 5, 1975, he died of congestive heart failure in New York.

In 1952, Tatum was elected to the National Academy of Sciences. He shared the Nobel Prize in 1958 in Physiology or Medicine with George Beadle and Joshua Lederberg. Tatum held a membership in the American Philosophical Society. He had the position of president of the Harvey Society from 1964-1965. In 1958, Edward Lawrie Tatum and George Wells Beadle received the Nobel Prize for Physiology or Medicine for their discovery relating to gene regulation. This coveted accolade was co-shared with Joshua Lederberg. Tatum’s other honors included the Remsen Award of the American Chemical Society (1953). He was on the editorial board of scientific journals such as Genetics, Science, and the Journal of Biological Chemistry. Tatum also served as a scientific advisor on many boards and helped set the national policy on training students and postdoctoral fellows.

Tatum was known to be a very caring and understanding boss. He had personal goals for his lab but enthusiastically motivated his students with their research interests.

For a video of the famous experiment of Tatum and Beadle, visit:

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