LB (Lysogeny Broth) Medium

• LB (Lysogeny broth, also known as Luria-Bertani) is the most commonly used growth medium to culture members of the Enterobacteriaceae including Escherichia coli (E. coli). 
• In molecular biology laboratories, laboratory strains of E. coli are grown in LB medium for recombinant DNA work. It is an excellent choice to grow E. coli for most molecular cloning (plasmid amplification and manipulation) and recombinant protein production-related experiments. 
• The LB medium was originally formulated by Giuseppi Bertani in 1951 for studying lysogeny in Escherichia coli (Bertani, 1951). The original recipe contained 1% bacto-tryptone, 0.5% yeast extract, 1% NaCl and 0.1% glucose. The latest widely used versions of LB medium do not contain glucose.
• Miller broth and Lennox broth are the two most popular and commonly used LB medium versions. They differ only in the concentration of sodium chloride. Miller LB Broth contains twice the concentration of sodium chloride present in Lennox LB Broth.
• Another version, the Luria LB Broth, contains a very low concentration, 0.05%, of sodium chloride.
• These versions allow researchers to select the optimal salt concentration for the growth of a specific strain of E. coli.
• LB is a rich medium that fulfills all nutritional requirements for the fast growth of E. coli. It contains bacto-tryptone, yeast extract, and NaCl.
• Bacto-tryptone, a special type of tryptone commonly used for the preparation of microbial culture medium, is a pancreatic digest of casein (also called Peptone C). It functions as an amino acid source for microorganisms. 
• Yeast extract provides vitamins and other certain trace elements. 
• NaCl concentration determines the osmotic condition of the LB medium, therefore, is an important determinant for appropriate growth conditions for a particular bacteria.

Composition 

• LB medium (Bertani, 1951):  1% bacto-tryptone, 0.5% yeast extract, 1% NaCl, 0.1% glucose pH adjusted to 7.0 with 1N NaOH. Lysogeny
  
• LB (Lysogeny Broth) Medium, Miller Broth: 1% bacto-tryptone, 0.5% yeast extract, 1% NaCl
• LB (Lysogeny Broth) Medium, Lennox Broth : 1% bacto-tryptone, 0.5% yeast extract, 0.5% NaCl
• LB (Luria Bertani) medium, Luria broth : 1% bacto-tryptone, 0.5% yeast extract, 0.05% NaCl

REFERENCES

• Bertani, 1951. Studies on lysogenesis. I. The mode of phage liberation by lysogenic Escherichia coli. J Bacteriol. 62(3), 293-300. PMID-14888646; Full-Text Link: asm, PMC
• Lennox, 1955.  Transduction of linked genetic characters of the host by bacteriophage P1. Virology. 1(2), 190-206. PMID-13267987; Full-Text Link: sciencedirect