LB media formulations have been an industry standard for the cultivation of Escherichia coli as far back as the 1950s. These media have been widely used in molecular microbiology applications for the preparation of plasmid DNA and recombinant proteins. Vitamins and certain trace elements are provided by yeast extract. Sodium ions for transport and osmotic balance are provided by sodium chloride. Tryptone is used to provide essential amino acids to the growing bacteria. LB Agar, Miller contains 10 g/L of sodium chloride, different from the levels in Lennox formulations. This allows the researcher to select the optimal salt concentration for a specific strain.