Specialized Transduction

As the relationship between the molecular structure of DNA and genetic properties became a possibility, lambda bacteriophage became of immediate importance. One of the first areas of lambda research was in transduction: some bacteria and lambda phage led to the distinction between HFT (High Frequency Transducers) and LFT (Low Frequency Transducers). HFT lysates are formed by induction of transductant heterogenotes (not standard lysogens). A brief discussion of specialized and general transduction follows.

See "The Bacteriophage Lambda" by A. D. Hershey, 1971, Cold Spring Harbor Press.

1. Lambda bacteriophage infects E. coli. and is injected through the bacterial cell wall into the bacterial cytoplasm.
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2. Lambda DNA is linear, but the two cos sites at terminal ends of the linear DNA join, thus becomes a circular plasmid in the bacterial cytoplasm.
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3. The lambda plasmid replicates in the prokaryon (in the case of Lambda, creating about 100 copies of the virus using rolling-circle replication), until the procaryon lyses under direction of the viral DNA, releasing the copies of the virus into the environment, ready to resume the cycle of infection. This autonomous replication is refered to as the "lytic" cycle; it takes about 50 minutes for lambda, at 37°C.
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4. Alternatively, the lambda plasmid becomes covalently bonded to the bacterial DNA. (Lambda DNA so bonded is then called a prophage.) This often happens at specific binding sites (attP phage site lines up with attB bacterial site, then via Holliday structures, the Lambda DNA changes conformation into a supercoiled helix, using gyrase) and is integrated into the Bacterial DNA. (DNA that closely neighbors the bonding sites are of special interest.) Viral DNA directs the covalent bonding to the bacterial DNA, but also simultaneously represses the lytic cycle for the virus. A bacterial strain carrying a prophage is called a lysogen. The process of creation of the prophage is called lysogenization. ¹ Lambda has three genes cI, cII, and cIII that are necessary for lysogenization (D. Kaiser, 1957). The prophage that is quiescent can be induced by UV radiation to enter the lytic cycle. (UV radiation deactivates CI repression protein.) CI represses the creation of cytoplasmic viral particles, simultaneously preventing reinfection by lambda. Interestingly, a cI mutation was found that makes the repressor thermolabile. Thus the prophage is quiescent but will lyse and enter into the productive state if the temperature is raised to a specific threshold.
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5. Cell division of the prokaryon takes place (now inheriting the prophage)
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6. At some point, perhaps due to UV radiation, the less stable prophage may be excised from the bacterial chromosome, effectively mimicing the DNA repair.
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7. The excised DNA of the prophage replicates, making multiple copies of the viral DNA, as well as capsids and tails, all assembled under a gene sequence into new lamba virus.
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8. Sometimes, transduction takes place. The prophage lyses from the bacterial DNA, but takes along ADDITIONAL, nearby, neighboring parts of the bacterial DNA as a unit of transduction. These new sequences of bases replace parts of the lambda DNA. The entire excised portion of the lambda plus new Bacterial DNA must be able to fit into a capsid (either too small, or too large, and a defective virus may result). λ_dg was used to denote the case where there is "defective galactose" transduction.
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9. The "transduced" viral prophage along with the neighboring bacterial DNA, becomes a new virus, capable of infecting more bacteria. However, the additional piggy-backed bacterial DNA will now also infect other bacteria. An example of this is bacterial DNA that codes for drug resistance. Thus drug resistance can very quickly infect other bacteria.
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10. The gal (galactose metabolism) marker as well as the bio (biotin synthesis) marker may be transduced independently. Different mutants of gal were examined.² Thus λ gal may transduce gal ⁺ and λ bio may transduce bio ⁺ independently, but as both the gal and bio markers are in close proximity, it is possible to simultaneously cotransduce gal ⁺ bio ⁺.
       Possible Transduction Crosses:
    • gal⁺ bio^–
    • gal^– bio⁺
    • gal⁺ bio⁺
    Thus using transduction and cotransduction, it is possible to create gene maps based upon linkage (A. D. Hershey and R. Rotman).
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11. The section discussing Bacteriophage Lambda also notes that Esther M. Zimmer and Larry Morse discovered that Lambda could be a heterogenote (a prophage that does not contain the entire lambda prophage, for example, a transductant).
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12. A detailed discussion of the Fertility Factor F (discovered by Esther M. Z. Lederberg) will not take place here. However, Esther M. Lederberg also noted that F' (the prophage of the Fertility Factor F) also participates in specialized transduction, the host being Salmomella typhimurium.

"While Zinder was pushing forward the work on Salmonella transduction, Lederberg's laboratory was continuing work on all aspects of genetics in Escherichia coli K-12. As discussed in Section 7.5, phage lambda was discovered in this strain by Esther Lederberg in 1951, and its linkage to the gal locus was shown by mating (Lederberg and Lederberg, 1953; Wollman, 1953). M. L. Morse, a student of Lederberg, attempted to determine if lambda was capable of transduction. Of numerous genetic markers tested, only a cluster of genes for galctose fermentation were transduced by lambda lysates (Morse, Lederberg, and Lederberg, 1956a). Also, transducing lysates could only be obtained by induction of lysogenic strains; lytic infection by free lambda phage particles did not result in transducing lysates. Since lambda prophage was linked to gal (see Section 7.5), the restriction of transduction to the gal region suggested a different and more special situation in lambda transduction than that for P22 in Salmonella. Because lambda transduction was restricted to only a few genes, it came to be called specialized transduction."
"The Emergence of Bacterial Genetics," Thomas D. Brock, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY, 1990, pp. 202-203.

It should be noted that the book above presents a biased view in favour of Joshua Lederberg: "...the work of Joshua Lederberg..., whom Brock has chosen as the hero of his story." See the review of the above book by Gunther S. Stent, Nature, 39: 661-662, Feb. 1991.

The importance of specialized transduction in lambda was commented upon by Norton Zinder himself in Current Contents 20, May 16, 1983 (p. 30). In this article he referred to Zinder, N.D. and Lederberg, J., "Genetic exchange in Salmonella," J. Bacteriol. 64: 679-699, 1952. Summarizing part of the article, Norton Zinder refers to genetic transduction, and notes that "we knew nothing about phage or temperate phage at the time." With reference to genetic transduction (not specialized transduction), he further points out that:

"General transduction³ provides the means for a fine genetic analysis of genome structure. The discovery shortly thereafter of special transduction⁴ complemented [general transduction] ... the paper also describes phage P22 (then called PLT-22), which became, with lambda, special transduction, the two paradigms for the study of temperate bacteriophages."

To get an idea of how much research was accomplished by the collaboration of Esther M. Zimmer Lederberg and M. Laurence Morse, examine the Galactosemia correspondence displayed at this website. Much of the correspondence, indeed, is focused upon gene mapping based upon transduction. Almost all the research on the relationshp between lambda and gal transduction was personally performed by Esther M. Lederberg and M. Laurance Morse, which is clearly shown in the correspondence (Joshua Lederberg was not involved in experiments). This is not surprising, since both Esther M. Lederberg and M. Laurance Morse were excellent experimentalists and, as other research scientists (such as Stan Falkow and Joshua Lederberg himself) have pointed out, Joshua Lederberg was not gifted with this ability. ⁵

As a note, the Fertility Factor F (the first episome discovered, and discovered by Esther M. Lederberg) is also capable of transduction. In "Episomes" by Allan Campbell (Harper & Row, NY, 1969), on page 105:

"The F episome resembles phage lambda in occasional occurrence of variants that have picked up genes from the bacterial chromosome. As with lambda, such variants are produced only from integrated F (i.e., from Hfr strains) and seem to comprise continuous blocks of genes contiguous to the F attachment site of the particular Hfr strain used."

Thus the lambda phage discovered by Esther M. Zimmer Lederberg was of major importance in explaining transduction. For a list of related papers, click here.

¹ Multiple plasmids (if compatible) may be found in one prokaryote cell. In some cases, the different plasmids may lysogenize, forming several prophages simultaneously in the same prokaryote chromosome. As an alternative to the process described here for lambda phage, Mu (for "mutations") is another bacteriophage that works quite differently than lambda does. The Mu virus injects its linear DNA into the bacterial host (E. coli) cytoplasm. The linearized phage DNA remains linear in the host cytoplasm (subject to degradation) and integrates into the host DNA as a "prophage". Now, by replicative transposition (θ structures, or Shapiro intermediates), multiple copies of the Mu prophage are created in the host DNA (directly, not in the cytoplasm)! When excision takes place, multiple copies of the Mu DNA are then assembled into capsids, tails are assembled, and heads and tails are joined. The host cell bursts (using proteins that attack the host cell wall just as lambda does), releasing the multiple copies of Mu virus into the environment to further infect new host bacteria.

² Lambda forms its prophage at a specific location in the E. coli chromosome (at site "attP" in the prophage [250 base pairs], "attB" is the matching bacterial DNA site [21 base pairs]). Thus only a few closely neighboring markers may participate in specialized transduction. Although taking place with far less probability, if "attB" is defective or absent, alternate sites with similar base sequences may participate in lysogeny, and thus different genes may be specially transduced. Other viral plasmids are not so restricted to specific bacterial sites, and as their prophages are not restricted to a specific location, these viral prophages can have many closely neighboring markers. This is generalized transduction. For this reason, lambda transduction is classified as specialized transduction and led to most of the detailed knowledge about how transducion actually functions.

³ "Transducing fragments in generalized transduction by phage P1", Ikeda, H. & Tomizawa, J., J. Molec. Biol. 1965, 14(1), 85-109

⁴ "Transduction in E. coli K-12", Morse, M., Lederberg, E. & Lederberg, J., 1956, Genetics, 41(1), 142-156

⁵ Thus major contributions to understanding specialized transduction and transduction in general came from the experiments by Esther M. Lederberg, Larry Morse, Joshua Lederberg, Norton Zinder, Allan Campbell, Werner Arber, etc. Citations are not provided as the number of relevant papers in this area from 1951 through 1956 and after is so large. In addition to the extensive correspondence with Larry Morse concerning specialized transductions with galactosemia, there also is an extensive correspondence concerning maltophilia research between Esther M. Lederberg and researchers such as Julius Adler, Enrico Calef, and Franco Guerrini (among others) concerning transduction and defective lambda.

Explanations at greater depth involving topics discussed here may be found in the following two sources:

1. "Lateral DNA Transfer: Mechanisms and Consequences", by Frederic Bushman, Cold Spring Harbor Laboratories Press, 2002
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2. "Fundamental Bacterial Genetics", by Nancy Trun and Janine Trempy, Blackwell Sciences Ltd., 2004

Related papers authored or co-authored by Esther M. Zimmer Lederberg:

1. Lederberg, E., 1950-1951, "Lysogenicity and Transduction E. coli", referenced in 1957, "Symposium on Bacterial and Viral Genetics (Canberra, August 1957)", p. 71

2. Lederberg, J., Lederberg, E. M., Zinder, N. D., Lively, E. R., 1951, "Recombination analysis of bacterial heredity", Cold Spring Harbor Symposia on Quantitative Biology 16:413-443

3. Morse, M. L., Lederberg, E. M., Lederberg, J., 1956, "Transduction in Escherichia coli K-12", Genetics 41:142-156

4. Morse, M. L., Lederberg, E. M., Lederberg, J., Sept. 1956, "Transductional heterogenotes in Escherichia coli", Genetics 41(5):758-779