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The Sol Spiegelman Papers

Letter from Joshua Lederberg to Sol Spiegelman pdf (106,720 Bytes) transcript of pdf
Letter from Joshua Lederberg to Sol Spiegelman
Number of Image Pages:
1 (106,720 Bytes)
1951-11-25 (November 25, 1951)
Lederberg, Joshua
Spiegelman, Sol
This item is in the public domain. It may be used without permission.
Exhibit Category:
Enzymes and Genetics, 1940-1955
Metadata Record Letter from Sol Spiegelman to Joshua Lederberg (November 28, 1951) pdf (50,413 Bytes) transcript of pdf
Box Number: 6
Folder Number: 42
Unique Identifier:
Document Type:
Letters (correspondence)
Physical Condition:
Series: Correspondence, 1946-1983
Folder: Lederberg, Joshua, 1946-1978
November 25, 1951
Dear Sol:
Seymour relayed your request for more details on preservation of microbes on silica gel. The basic principle is obvious: to use a chemically inert dessicant so that it need not be separated from the microbes. It was hoped that adequately dried bacteria could not be influenced by the presence of oxygen, so the procedure has consisted simply of adding a small volume of concentrated suspension to a pre-sterilized tube of the gel, then sealing off directly. If the tubes have to be evacuated, several extra steps (constricting tubes with a torch,; evacuating, and then sealing) are needed, and there would be no advantage over the technique used by Brown, Hershey, Lindegren, etc.
I wish I could report a well-developed method, but a good deal of experimentation of a rather odious sort (with long waiting periods) is still needed. With cells suspended in peptone, there is a process loss of 1-2 bels, and over a 90 day period a continued attenuation amounting to about 5 bels per year. At this rate, a year would be the maximum, but all depends on whether the attenuation curves continue, or fall off. I have been using several types of silica gel from the Davison Company, Baltimore, Md. Their purest grade is "Code 40", 6-16 mesh, and sells for about .70 per pound.
There are at least two innovations that should be tried: a protein menstruum rather than peptone, and perhaps adding the suspension to a layer of filter paper or glass or the like just over the silica column. Most of all, I don't know the optimum moisture conditions: I suspect that it is rather easy to obtain preps. that are too dry. Published work refers to 1-2% residual moisture as optimal by the standard methods, but it is rather difficult to calculate the vapor pressure over the cell mass, which is the critical and controllable parameter when silica is used. The usual methods do not establish a true equilibrium between the cells and the dessicant or vapor trap, and the dessicants used (e.g. CaCl2) probably have to be calculated at the vapor pressure of a saturated solution, considering the quantities usually prescribed.
Here is a good example of a technical innovation that has a theoretically sound basis, and that would be very worthwhile (especially to geneticists with thousands of cultures), but which may require an amount of empirical work that would be prohibitive for one person (like myself). In some respects, it would make an excellent problem to be approached from a biophysical point of view, and one that would have important implications for general biology: what is a viable, dried cell? Meanwhile, I have been playing with the system a bit, in rather discouraged fashion. Silica gel is excellent for short-term preservation and mailing cultures. Perishability, especially with respect to freezing, is greatly reduced.
Sincerely, Joshua Lederberg
[HANDWRITTEN NOTE: P.S. The vials are Cat. No. 111
F. J. Stokes Mfg. Co. Phil. Pa.]
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