August 24, 1953

Dear Dr. Rowley:

I mist apologize for this tardy reply to your letter of July 15.
I was away on a trip to San Francisco during midsummer, and this is
ay first opportunity.

Your letter asked about crossable strains of E. coli for virulence
studies. I agree strongly about the desirability of working with strains
with which some genetic analysis will be possible. I think it would be
equally important to deal with cultures Whose serological properties
are also easily classified. We are making slow pro—
gress in accumulating and organizing genetic and serological information
on our large group of new strains. For many of them, we have pnly the
reasénable assurance that they will undergo recombination, though some
are much less fertile than others. We have also been collecting some
information on the recombination of antigenic markers. At the moment,
unfortunately, this work is in a rather disorganized condition. Auxo—
trophié mtants have been prepared fn only a few lines for the furtherance
of the crossing studies, and in many lines, colonial and serological
variability has been noticed (and not yet adequately studied) which
will have to be clarified before toxleity tests will be entirely meaning-
ful. For these reasons, there are only a few cultures which would be
appropria&e for your studies. Perkaps I am misconstruing your require-
ments, and a clearer statement of them would facilitate the exchange.

Dr. T. C. Nelson mentions having heard recently from you of your
plans t& spend some time in Paris, If you find it convenient to do so
upon your return to London, I will be glad to renew this discussion with.
you. Perhaps by that time, we will have shaped our collection into a
more satisfactory form.

Would you be interested in a similar analysis with Salmonella (e.g.
S. typhimurium)? There is no question here of providing strains, as they
are innumerable and almost all are technically feasible for genetic
transduction analysis, but if I can be of any assistance in describing
methods and the like, I would be happy to do so. On the other hand you
might find it equally convenient to consult with Bruce Stocker or Clive
Spicer.

Yours sincerely,

Joshua Lederberg