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Letter from Joshua Lederberg to Emma Klieneberger-Nobel

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  • Physics


Departgent of Genetics, University of Wisconsin Madison 6, Wisconsin December 13, 1951 Dear Dr. Klieneberger-Nobel: I was pleased to note (for my part) your preoccupation with E. coli K-12. I must, admit that your letter did not give a very clear indidation of l*itll, that ia your morphologioal observations, but perhaps you did not wieh to commit yourself prematurely. Your schedule for making up the medium appears to be quite satiafxctory. We have used distilled rater, but unless the tap water Is incredibly contaminated with growth factors, it will work quite well instead. The effect of the tap water in stiffening the qgar is probably its hardness (ca and Ug), not the pH, for there is too much phosphate buffer in the medium for its final pH to be so readily modified. As a rule, we have not bothered to ateam the sugar. The salts are weighed out and dissolved in one aliquot of water, the sugar and agar in another. Theso are then autoclaved Beprtrately, and nixed in equa;l. proportions bef<?re the medium is poured. Some residual growth of the atant cultures ia to be expec- ted, but the recombinant prototrophs should stand out aa well-developed colonies againat a barely visible ba&gr2uod. If we knew of any conaisterlt way of inc2e~s~ing the rate of recom- bination, we should, of course be using it consistently. It has been reported that awssure ul the ~~-161 parent ceZls to small doses of ultraviolet light will increase their recombining propensity. %a have not verified this for ourselves, 28 got, but-. it would be mrth trying. I am not 8ure what controls will be possible. The same morpho- genatic sequencea t&t ;peratcr 2?5 bBtl*,:?c!n 5R-lS? x ;'r--llt?7 undoubtedly occur within a K-12 culture, r*ltho;rgh :uithout ;snetical&+aningful consequences. I I am not sure &at msdiun you api;! rsftir2ing ts in your question' about alcalinizat;ion. The miniolol aedium would bost be alsaldihized by alter- the proportions of the K;?HP04 : KH2FOit to give

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