Persistant phenotypic differences (serial subculture)?

Michael Benedik benedik at uh.edu
Tue Jun 4 10:43:47 EST 1996


In article <graham.833835674 at biodec.wustl.edu>
graham at biodec.wustl.edu (James Graham) writes:

> Hello folks. Here's an interesting problem which I've yet to hear
> any good ideas on, but one which has become increasingly evident in my 
> work, yet is apprarently largely unrecognized in the area of my research.
> 
> 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.
> 
> Personally, I have noticed some time ago that Staphylococcus aureus cultures 
> grown in a defined medium with 0.5 M NaCl frequently (but not always) grow 
> in visible clumps to a greater extent than when grown at higher or lower 
> salt concentrations. More importantly for this discussion, those cultures 
> which show the clumped or "smooth" growth characterisitc will continue to 
> show such growth in multiple subsequent serial batch subcultures, as if 
> some kind of "founder effect" could be propagated under otherwise identical 
> conditions.
> 
> Is there any evidence for such a "heritable" change in gene expression 
> in bacterial cells growing in batch cultures? If so, how many 
> such serial subcultures would it take to obtain two identical patterns 
> of gene expression among two cultures of the same strain taken from two
> different inocula? What is the nature of the propagation of the 
> phenotypic differences in these cases? Do the intial inocula perhaps 
> conditionthe culture media differently? Do regualtory cascades perpetuate 
> different types of gene expression among the progeny of differently 
> cultured cells growing under identical conditions? If so, through how 
> many batch subculturings can such effects persist?
> 
> Any refereneces to such discussion or experiments most appreciated.
> 
> Thanks. Please send me a copy of any responses directly.
> 
> Jim
> J. Graham PhD 
> Biology Department 
> Washington University of St. Louis 
> 

Jim,

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
component.

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
rates.

Let me know if you learn anything.




Michael Benedik
Department of Biochemical Sciences
University of Houston
benedik at uh.edu



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