In <1993Sep21.144753.28960 at abo.fi> METZLER at ALA.BTK.UTU.FI (Mary Metzler, Plants, x8076) writes:
> 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
I have an idea that may appear rather prosaic and maybe just plain
stupid, but I don't know enough about antibiotics to be sure.
Perhaps the gene product that provides resistance is converting
the antibiotic into food, i.e. a molecule that can be broken down
to provide energy. Your agar might be meagre enough for this to
make a difference. Just a thought.
Inst. Exp. Path.