Micro Journal Club: E. coli competence

[Tom Schneider]

In article <9409130130.AA03289 at mendel.Berkeley.EDU> kuehn at MENDEL.BERKELEY.EDU
(Meta Kuehn) writes:

| There are both basic and more complex questions to consider:  What are the
| factors that are involved in making E. coli competent for DNA uptake?  How
| might the cell cycle effect the competence of E. coli?  Is competence
| associated with cell division?

I am curious what is causing the change in competency.  If we understood that,
perhaps we could always set our cells on the peak and get great
transformation efficiencies consistently.

I thought of several models to explain the competency peaks:

1. Cell density increases cell-cell contact.  Somehow cells read this and
respond accordingly.

2. Cells use up something in the medium and this is sensed by them
and causes competency.

3. Cells put something into the medium, a kind of hormone or signal, that is
read by other cells.  This could be a positive factor that turns on competency
or a negative one that prevents it.

It's hard to see how a single mechanisms like this would produce two peaks, so
it is possible that the peaks are generated by different mechanisms, or by two
different stages of one mechanism.  It's especially hard to understand model 1
by only one mechanism.

What I find intriguing about this paper is that it suggests communication
between the cells.

If there is some component in the medium, then it's easy to do some experiments
in a day or so to determine that it exists!

For example, start a big culture of cells growing and take a series of
samples.  Spin down each sample and (I suppose) put on ice.

Grow another batch of cells to a point where they have low competency (to look
for a stimulating factor) or high competency (to look for a suppressing
factor).  Spin these cells down and resuspend them into each of the cultures
made in the first part of the experiment.  Then go and transform them.  If the
transformations with the same amounts of DNA give different results, then there
is a factor and one can begin to isolate it.

A similar experiment could be done to test model 1.  Use primary cells that
have a drug resistance like str.  Mix in different amounts of another cell that
doesn't have that resistance.  Transform in a plasmid for amp resistance and
select on amp and str plates.  This way one would see the effect of having cell
density increased without getting the extra cells in the way.  (Of course one
has a bunch of control experiments to do and one has to know the frequency of
getting str resistant strains.)

I don't have the time and energy to do the experiment, though it's so easy it's
very tempting!  If someone does this, it would be neat to see it on the net,
but I fear that you'll go off and publish so we won't know for a year or so
...  ;-)  Just say you got the idea here ... ;-)  On the other hand, it
would be neat for several groups to try these experiments and then discuss them
on the net.  Perhaps one paper with several names on it would come out.  I'd
like to see that because the potential for this kind of widespread
collaboration could be a very powerful use of the net.

  Tom Schneider
  National Cancer Institute
  Laboratory of Mathematical Biology
  Frederick, Maryland  21702-1201
  toms at ncifcrf.gov
  http://fconvx.ncifcrf.gov:2001/~toms/info.html