M9 Medium: M9 Broth is a minimal medium, based on the M9 Minimal Salts1, which supports the growth of Escherichia Coli. This medium is useful in maintaining positive selection pressure on plasmids coding for substances such as amino acids or vitamins. It can also be used to maintain bacteria for use with M13. M9 Broth can be supplemented with specific amino acids or other metabolites that allows for specific selection pressures that the researcher may require. M9CA Broth also supports the growth of recombinant strains of Escherichia Coli. This media is supplemented with casamino acids, which provides the bacteria with a rich source of nitrogen that they can use during growth. The M9 and M9CA Broths contain ammonium chloride, which provides a source of nitrogen. They also contain potassium and sodium phosphates. The phosphates are used to buffer the media against changes in pH due to metabolism, and the sodium chloride is used to help maintain isotonicity within the medium during growth. Supplements such as glucose, magnesium, and calcium are used to enhance the growth of the bacteria. Glucose is added as an additional carbon source, and magnesium and calcium are added to increase the growth of recombinants. The magnesium sulfate is a source of magnesium ions which are components in the enzymatic reaction during DNA replication.