M9 Minimal Salts, with additions, is used to prepare M9 Minimal Medium, which is used to cultivate recombinant strains of Escherichia coli. M9 Minimal Salts is combined with a selected carbon and energy source (e.g. Dextrose) to create a minimally nutritious, chemically defined culture medium for recombinant Escherichia coli growth and culture maintenance. The ability to tightly control the nutritional content of the medium allows for the continued selection for specific plasmids encoding the ability to produce necessary vitamins and amino acids missing from the nutritional complement of the medium. By further supplementing the M9 Minimal Medium with selected amino acid or other necessary metabolites, it is possible to create a selection medium designed for specific auxotrophs, greatly expanding the flexibility of this medium to select for and support the growth of very unique recombinant Escherichia coli strains.