Lysogeny broth (LB), a nutritionally rich medium, is primarily used for the growth of bacteria. The acronym has been incorrectly interpreted as Luria broth, Lennox broth, or Luria-Bertani medium; according to its creator Giuseppe Bertani, the abbreviation LB was actually intended to stand for lysogeny broth.[1] The formula of the LB medium was published in 1951 in the first paper of Bertani on lysogeny. In this article he described the modified single-burst experiment and the isolation of the phages P1, P2, and P3. He had developed the LB medium to optimize Shigella growth and plaque formation.[1][2]
LB media formulations have been an industry standard for the cultivation of Escherichia coli as far back as the 1950s.[3][4][5][6][7] These media have been widely used in molecular microbiology applications for the preparation of plasmid DNA and recombinant proteins. It continues to be one of the most common media used for maintaining and cultivating laboratory recombinant strains of Escherichia coli.[8] For physiological studies however, the use of LB medium is to be discouraged.[9]
There are several common formulations of LB. Although they are different, they generally share a somewhat similar composition of ingredients used to promote growth, including the following:
Peptides and peptones are provided by tryptone. Vitamins and certain trace elements are provided by yeast extract. Sodium ions for transport and osmotic balance are provided by sodium chloride. Bacto-tryptone is used to provide essential amino acids to the growing bacteria, while the bacto-yeast extract is used to provide a plethora of organic compounds helpful for bacterial growth.
In his original 1951 paper, Bertani used 10 grams of NaCl and 1 gram of glucose per 1 L of solution; Luria in his "L broth" of 1957 copied Bertani's original recipe exactly.[6] Recipes published later have typically left out the glucose.
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The formulations generally differ in the amount of sodium chloride, thus providing selection of the appropriate osmotic conditions for the particular bacterial strain and desired culture conditions. The low salt formulations, Lennox and Luria, are ideal for cultures requiring salt-sensitive antibiotics.[10]
The following is a common method for the preparation of 1 liter of LB:
Prior to autoclaving, some labs adjust the pH of LB to 7.5 or 8 with sodium hydroxide. However sodium hydroxide does not provide any buffering capacity to the media, and this results in rapid changes to the pH during bacteria cultivation. As a result, some labs adjust the pH of LB with 5–10 mmol/L TRIS buffer, diluted from 1 mol/L TRIS stock.
High density bacteria cultures require more buffering capacity than 5-10 mM TRIS can provide.