In the paper that introduced TRANSDUCTION (J Bacteriol. 1952 Nov;64(5):679-99.), Lederberg and his student Zinder reported that S. typhimurium "LT-22 is lysogenic for a virus active on LT-2. This virus is capable of inducing lysogeny in LT-2."
I read this line as: LT-22 carries a prophage that, upon induction, can infect LT-2 and establish a prophage in this cell.
Thus, I am expecting genes to pass from LT-22 (actually, its mutant LA-22) to LT-2 (that is, its mutant LA-2).
Instead, "prototrophs (that is, the recovered strains) appeared in the plating of LA-22 but not of LA-2... thus, LA-2 produced a filterable agent... that could elicit prototrophs from LA-22".
But LA-2 does not carry prophages. Thus, how did this experiment work?
Even assuming that LA-22 produced phages that infected LA-2 and then moved back to LA-22 with additional genes, LA-22 should have been refractory to subsequent infection with this phage.
Is there a detailed explanation of this experiment?
Thank you
I think that, as you mention, LA-22 produce phages that infect LA-2 and generated transducing lysates. However your assumption that LA-22 would be refractory is not correct. A lysogen is generally resistant to an infective cycle of the phage (ie phage 22 would not infect and form plaques on a lysogenic strain) but that doesn't mean the DNA is not injected. So if the DNA gets in the cell then transduction occurs through homologous recombination with the chromosome and does not require phage replication.
In a paper on Scientific American (https://www.jstor.org/stable/24944819), Zinder simply commented that:
One of the two strains always acted as the donor and the other as the recipient of the genetic tract. One of the two strains (the recipient) [PA-22] carried a temperate virus… the second strain (the donor) [PA-2] was especially susceptible to this virus. When the two were mixed, an occasional infective virus developed in the recipient strain and invaded a cell of the donor strain.
In the figures, though, there is a simple flux from the donor to the recipient, not a two-way trip.
But in a paper by Parkison (Article Classic Spotlight: the Discovery of Bacterial Transduction
), the solution to the riddle is like you suggested:A filtrable agent (FA) was evidently responsible for transduction activity.
It must have moved from the LT-22 culture through the filter to the LT-2 side of the U-tube, where it induced FA activity, which then moved back across the filter to produce prototrophic recombinants in the LT-22 cells.
Thanks
in both snippets of text they say the same thing, that a viral lysate is generated in LT2 (PA2) and then infects and transducers the original LT22 (PA22) strain. You can transduce a lysogen but the infecting phage won't replicated in a lysogen.
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