In article <4apgpk$e7p at epx.cis.umn.edu>, shin at biosci.cbs.umn.edu (Shin
> Paul N Hengen (pnh at kaylor.ncifcrf.gov) wrote:
> : Shin Enomoto (shin at biosci.cbs.umn.edu) wrote:
> I meant cold-sensitive by cs. I have not caculated how many divisions
> XL1-blue and DH5alpha are going through, but I am pretty sure they are
> not dividing efficiently. Every other strain that I have tried to grow
> at 18C (SURE, MC1066, C600) I need to do at least 1/20000 dilution at 5pm
> to be harvesting at similar density as XL1-blue and DH5alpha. I
> got 10^8 for MC1066 and C600 and 10^7 for SURE, but not 10^9. I was
> wondering if high effeciency that I get sometimes with XL1-blue and
> DH5alpha had anyting to do with inability of these two strains to grow at
> low temperature.
>> Well, SHURE, MC1061 and C600 do have wild-type recA gene, wereas
DH5alpha and XL1-blue are recA-. It is known that recA- strains grow
slower and form smaller colonies than their recA+ counterparts.
Apparently, the difference is even more profound at lower temperatures.
Pure speculation: if E.coli is most succeptible to treatment that makes
its cells competent at certain stage of its cell cycle AND if slower
growth of the cells at lower temperatures makes E. coli stuck at this
stage OR if slower growth allows to obtain more synchronous culture, then
the slower the growth, the more cells in the population are succeptible to
treatment at lower temperature---> the higher is potential efficiency of
transformation. On the other hand, recA mutation has lots of consequences
for cell physiology. It is likely that some of the consequences are
beneficial at some stage of preparation of competent cells and/or
transformation of competent cells.