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Letter from Joshua Lederberg to Bernard D. Davis

Publication Date
  • Medicine


August 22, 1951. Dr. Bernard D. Davis, Biologicsl Laboratory, @oods Hole, .&~a. Dear Bernie: The culture Under seat you: S%-435, was derived from a wild type labelled 1t22!' (our LT-22), a llphqe-type"r received from Lillesngen (Ada path. micr. scand.p Suppl. 77). In order to w..rk over other fertile strains of 5. coli, we will undoubtedly run into aromaticless m&ants, and havs soms already. There are also sollls in other Sakwnella strains, and a tryptophanaless and a phenylalaninsless in Pseudolmnas fluerescenas(which is eaeily handled on the same medti as E. ~01%). If any of this would be of interest to you, please let me know. Do you think a test for dominants of sulfonamide resistance wotid be feasible. The beauty of Sr is that there is a single step mutation that gives complete resistance. If you would be willing to furnish Bfr mutan,& in suitable stocks (preferably X-1177), X'd be glad to try to put the marker into a heterozygote. I had shied away from it thinking that the characterization and genetics might be messy if, as I thought a paiori there were a multi-step situation. Rather pd I have just about completed exper~n~ on indirect selection of Sr ati Vi mutants, us1 9 replica plating. These mutations indisputably occur in clones, and pure S crultures were ohtained by successive enrichment of populations whose history at no time included expseure to sm. I think I taked to you about this at CSH: the procedure is to pick the site on a plain agar plate, heavily inoculated and grown, corresponding to an Sr colony on a replica to sm medium. A more dilute plating is used for the next step, giving about UN-fold snrichment at each stage. The replica platiag works beautifuU,y for picking up auxotrophs (when penicillin hasn't done a/ perfect job), and is also helpful in characterization. If you should see Harry F%le, give him my best and then tell him about the indirect selection, would you. got that this excludes his story a

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