Micro Journal Club: E. coli competence

Meta Kuehn kuehn at MENDEL.BERKELEY.EDU
Mon Sep 12 20:30:22 EST 1994


Dear Fellow Netters:

I think we are ready to begin the first "coordinated" discussion of a
journal article Thurs. Sept. 15th.

An interesting and very short paper has come up (with thanks to contributor
Tom Schneider) regarding the cycle of E. coli competence.  Considering that
transformation of DNA into E. coli is important for most cloning projects
in many labs, it seemed an appropriate article of general interest.  In
addition to the obvious technical advance, it also brings up the question
of the biochemical basis for competence and how it is related to the cell
cycle.

Title:"The optimization of preparations of competent cells for
transformation of E. coli"
Authors: X. Tang, H.-O. Li, M. Zhang, H. Gao, A. Fujita, O. Sakatsume, T.
Ohta and K. Yokoyama
Reference:  Nucleic Acids Research (1994) V.22, N.14, pp. 2857-2858.

Summary: (Due to the brevity of the paper, there is no abstract, so I will
attempt to summarize the results here.)  The authors showed that the degree
of competence of several commonly used strains of E. coli changed during
their growth cycle.  The authors noted that normally protocols advise
densities of 1 x 10^8 cells/ml (OD600=0.3-0.4)  for optimal preparation of
competent cells using the calcium chloride method.  However, the authors
demonstrated that E. coli cultures experience 2 peaks of competence:  one
at the known OD=0.3-0.4 (5 x 10^7-1 x 10^8 cells/ml) and one at
OD=0.94-0.95 (4 x 10^8 cells/ml).  In addition, they showed that the second
peak  gave twice the tranformation efficiency.   Thus, they forsee two
benefits:  1) a greater amount of competent cells can be prepared which 2)
take up DNA at higher efficiency.  This method can be used for both RecA+
and recA- strains.

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?

Comments and discussion of any related topics (ie, competence in other
types of bacteria..) by any and all bionetters are encouraged.

JC disclaimer:  If the author(s) of the paper are listening, please forgive
and correct any errors made during the presentation or discussion of the
contents of the article.


Meta Kuehn





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