Persistant phenotypic differences (serial subculture)?
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
Washington University of St. Louis
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