So after bacteria have been transformed to perhaps grow up a plasmid of interest, why pick only a single bacterial colony from a selective plate for further expansion?
I understand that this is to ensure that you are only working with a single genetic makeup because each separate colony is derived from only a single bacterium. What I can't rationalize is that if I am trying to expand and isolate a plasmid of interest, all colony expansions on a selective antibiotic plate should contain my plasmid. So is it really necessary to take only a single colony, because all colonies I pick should be useful to me.