Dear Netters,
We have recently noticed a peculiar phenomenon with some of
the gram-positive bacteria which we work with. When we transform
the bacteria with a plasmid containing a gentamycin resistance gene
(using electroporation), we find that the size of the transformant
colonies depends on the concentration of the antibiotic, but not
in the manner one would expect. The colonies are bigger at higher
concentrations of gentamycin and smaller at lower concentrations
of antibiotic. We know that the plates are not labeled with incorrect
antibiotic concentrations because at the lower concentrations there
is a ring of bacteria growing around the edge of the plate - we always
spread our antibiotic onto the plate rather than incorporating it into
the agar, and this gives a lower concentration at the edges of the
plate - but at the higher concentration there is no ring.
The only idea I can come up with is that the gene is induced
only at the higher concentration. But wouldn't it be weird for a gene
not to be induced at lower, but clearly inhibitory concentrations
of antibiotic?
Any ideas anyone has about what is going would be greatly
appreciated, as well as any relavant references concerning anti-
biotic resistance gene expression and induction.
Thanks in advance,
Mary Metzler, Department of Plant Physiology
University of Turku
Turku, Finland
Metzler at sara.cc.utu.fi
