Persistant phenotypic differences (serial subculture)?

James Graham graham at biodec.wustl.edu
Mon Jun 3 16:35:43 EST 1996

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 

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.

J. Graham PhD 
Biology Department 
Washington University of St. Louis 

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