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January 26, 1955

Dear Bruce:

Helllo! I hope you are going to be patient with me about this manu-
script. It is no exaggeration that I have dropped everything else
@ abruptly tut in order to coneentrate an it, and try to resolve my
ambiguous thoughts about the problem.

Let me say to shart that my own experiments, with --x S666 almost
exclusively, papallel your results quite closely. I have not been so
fortunate as you, however, in being able to trace the descendancy of

g "E" cells over many generations, as you have. This must be due to the
rather lower incidence of "FE" cells in this system, and to what seems
a rather lower number of motile progeny, on &She average. What data I
do have (I've already sent you some) do indeed support the unequal
distribution of such progeny among sibs, but some of the numbers are
on the sgaky side of 10. (At least for now, do let me speak of a

; polycatenate = E, oligocatenate for the cells or clones with fewer

/ 2) motiles and (uni)-catenate for the strict "unilinear" case]. Most of

7 my earlier experiments were devoted to studying the life expectancy of
single mbaorta chains, for example one was followed to the 59th (sic)
generation after its intk initiation, which was certainly not less than
45 generations after its separation as a single chain. That is, I was
primarily concerned in getting as rigorous proof as pussible of the

(Uparticulate and non-peproductive character of the "motility-conferring-particle";

6)

this may be taken as amply settled on both sides of the Atlantic. In my experience,
however, I have almost never seen further increase in the number of chains after
about the 13-14th generation, which is simply to say I had never caught the poly-
catenate cell among the numerous chains already produced.

There are just two questions I am not altogether happy about: is there actually
an igcrease in the numbers of the mep's, in acctrd with your hierarchy of primary
and secondary chains, or is ig still poasible that all the mep's are already formed
in a polycatanate cell, and are then distributed albeit non-randomly at successive
divisions; and, how certain is the correspondence between polycatenate and trail-
forming cells? As to the first, I am not greatly bothered by the dispppportions;
owing to the dmall numbers involved there is no good evidence that the apportionment
from oligocatenates is random either (how are your data on this?; my own offer
examples like 6:1:0:0 ; 7:1 ; 7:1:1:0 ; 7:4:0:0, which should be none too frequent
on a random basis.) And, indeed, I am rather more sympathetic than you to Bisset's
notion; some time ago I had done dome exneriments on TZ-labelled cells which suggested
that they regularly grew/from the pole opposite the TZ granule, which accounts for

(and divided) the subpolar position being maintained. In any
dyent, it is too uncertain that the mcf's are instantly flagella for our obeervations
to be decisive. Concerning the trails, I would not yet reject the role of ac-
deidental factors, as you state it at the bottom of 4g - 4h, and I think it will be
necessary to get more direct proof that unicatenates are nct, and polycatenates are,
able to form trails. In your experiment, is the Poisson distribution applicable?
That is, was the number of motile cells per drop uniform or normally distributed,

c. “hat was the number? I have been transferring drops with just one cell each
and have about a 50-60% successful recovery, but as told you before, virtually no
trails.
(Index Nos: for
conv. reference )

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Bruce, 1 would like you to bear with me on two possible courses, which I
should like to try simultaneously. One is a terser account, to be considered
preliminary, and designed say for the Proc Nat Acad Sci US,(where it can be pub-
lished within 10 ~ 15 weeks) where weg can summarize our accordant data, and
emphasize especially the unicatenate end of the story (which is the most
intewesting to mg mind, perhaps because least speculative). You can then follow
this up at your own convenience, and feel no hindrance from my part. Alternatively,
I will try to continue some mre experiments, including a look at your own
—x SW541 materhal, for example, to try and convince myself more definitely
of your choice among the alternative interpretations, one way or the other.

I have in mind particularly to look more closely at trails and the chemotactic
and physical factors that might be involded. Since an accidental experience
with phenol some time ago, as I may have written, I have no doubt of the
importance of tactic behavior, be it “apobatic" or "strophic".

Une other question: one way of correlating trails, swarma, and x-catenates
would be by considering the frequency of swarms as a common denominator. I think
you will agree that every cell that engenders a motile clone should be detected
as a awarm., Have you detailed data on the ratio of trails: swarms on one hand,
and poly—: oligoeeatenate: motile clones on the other? I have to collect my own
seattered pedigrees on this point, but offhand I would judge that they do agree
with your notion. I think I should like to take another look at —X SW967, which
forms such beautiful trails.

Query? Have you any more recent quantitative data on incidence of swarms and
trails per phage? In your "report" you estimated, for TM2 —x SW541 an efficiency
of better than 10~4 ! I don't recall any direct comparison; this must have been
what impelled me to make SW~665 (= SW541 Xyl-), transduction to which proved to
be only the usual, about 10-6, for Xyl

Do you account directly for the small incidence of polycatenates among
the initial iaolations? Do you think the others are all oligocatenate sibs?

ae ee enn ee a es oe ee ence ne

Just to be the devil's advocate, let me propose an alternative version(s).

1) in re trails, that owing to the lack of a chemotactic impulse, most motile
cells are content to swim and grow on the surface. Very few start a trail, and
those that do only after all of the motile cells are unicatenate. Ans: if
trail-formers are not distinctive polycatenate calls, it should be possible to
modify the incidence of trails either by manipulating the medium, or with chemitac
tic pressure. Will do.

2) in re polycatenates:"let us not multiply particles without necessity". We

can readily presume that, in transduction, some fragments implaat; others do

not and are lost. Meanwhile, even in the latter (which might be expected to be
most frequent) the gene has left its product. The product is not particulate (ne-
cessarily) but is sooner or later assimilated into mm particles (flagella). The
product is, however, not soluble and is disproportionately distributed. [Even
simpler would be the accumulation of flagella themselves, but it may be awkward
to think of accugulating as many as 100+ flagella. What do you think? What is the
maximum namber of chains you have dobserved?]. If you like, the intermediate pro-
duct (essentially equivalent to your "E pargicle") might be an enzyme which could
function only when present above a certain threshold amount.

1) and 2) are not directly dependent on one another. If I may state a

general outlook on the problem, it would be possible to postulate any number of
elements in the path from gene to flagella or motility; the genetic literature is
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aN

full of hypothetical hierarchies,and you can take your choice whether the inter-
mediate elements do or do not themselves replicate (cf. Sewall Wright&s reviews,
Amer. Natural., 793289; Ann. Rev. Physiol. 7:75; Physiol. Rev. 21:487, and
Splegelman's fantasies in CSH 1946 at p.271). The present case is unusually simple
in some respects, but we have an unknown numberg of parameters in the way thet

the transduced fragment might function. I want to distinguish, if we can, between
what is reasonable, and what is reasonably certain.

If I can find the time, on top of the two "zourses"t supra, I will try to set up
another tape by way of verbal commentary on the ms. Perhaps one reason for hesitancy
in using the tape is that I did not know whether you could conveniently listen in
private, as some comments are likaay to be designed as more intimate conversation,

Your
bw i. ——ammeaae

‘Joshua Lederberg

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