Persistant phenotypic differences (serial subculture)?
l.a.robertson at stm.tudelft.nl
Tue Jun 4 11:43:51 EST 1996
benedik at uh.edu (Michael Benedik) wrote:
>In article <graham.833835674 at biodec.wustl.edu>
>graham at biodec.wustl.edu (James Graham) writes:
>> When one grows several broth batch cultures of a single bacterial
>> strain inoculated from say an saturated overnight culture, a single
>> colony, or from a frozen glycerol stock, one will notice a variety of
>> differences between the two cultures, at least in terms of iducability of
>> promoters, or perhaps the transformation efficiency of subsequently prepared
>> calcium competent cells. Rumor has it that a two-dimensional PAGE
>> analysis of identically cultured cellls prepared from two cultures
>> originating from slightly different inocula will show considerable
>> differences, far beyond that which could be attributed to differences
>> among any nondividing cells originally introduced.
>Good observations. I too have been wondering similar things. We notice
>that we get very different levels of expression when we dilute an
>overnight culture 10e3-fold compared to 10e6-fold. (Looking at
>expression of extracellular nuclease from Serratia marcescens). And
>these are washed cells so it isn't carry over of some growth medium
>Obviously you should rule out differences in carry over of signal
>molecules in the growth medium.
>My guess it is a very slow turnover of some intracellular signal. But
>we have not spend any time looking at number of generations or of
This sounds very much like the changes in cultures that occur when they
are grown in continuous cultures - for example, growing them for long
periods at growth rates approaching mu max seems to select for
"turbo-bacteria" with much higher mu max values than the original
inoculum, growing them with low levels of antibiotics gradually produces
strains that can tolerate higher levels of antibiotics, etc. I've always
believed that its because any "pure culture" is actually a collection of
not quite identical bacteria - there will be a lot of the type that most
suit the particular growth conditions, but low numbers of others carrying
properties that are not really needed. Change the conditions (e.g. by
increasing the growth rate), and you favour one of the minority
populations which then becomes dominant. With the continuous cultures,
it's much more pronounced in heterotrophs than obligate autotrophs.
Isn't there a similar phenomenon with pathogens losing their
pathogenicity when cultured for extended periods on synthetic media?
Something seems to be echoing back from long-gone student days.....
Dr. Lesley A. Robertson
Kluyver Laboratory for Biotechnology
Delft University of Technology, the Netherlands
L.A.Robertson at stm.tudelft.nl
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