Lysogeny broth, a nutritionally rich medium, is primarily used for the growth
of bacteria. The initialism is also commonly, albeit incorrectly, taken to
mean 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. 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. 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. It continues to be
one of the most common media used for maintaining and cultivating laboratory
recombinant strains of Escherichia coli. For physiological studies however, the
use of LB medium is to be discouraged. 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 casein peptones Vitamins
Trace elements Minerals
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. Tryptone is used to provide essential
amino acids to the growing bacteria, while the 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. Recipes published later have typically left out the glucose.
Formulae 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. LB-Miller
LB-Lennox LB-Luria
Preparation The following is a common method for the
preparation of 1 litre of LB: Measure out the following:
10 g tryptone 5 g yeast extract
10 g NaCl Suspend the solids in ~800 ml of
distilled or deionized water. Add further distilled water or deionized
water, in a measuring cylinder to ensure accuracy, to make a total of 1 liter.
Autoclave at 121 °C for 20 mins. After cooling, swirl the flask to ensure
mixing, and the LB is ready for use. = Adjusting the pH =
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.To get around this some labs prefer to adjust the pH with 5-10 mmol/L
TRIS buffer, diluted from 1 mol/l TRIS stock at the desired pH. However, it is
not absolutely necessary to adjust the pH for most situations. Some labs adjust
the pH to 7.0 merely as a precaution. Since the buffering with Tris will also
be largely ineffective in the face of substantial bacterial growth, adjusting
the pH of LB in this particular manner is usually unnecessary. As such, use of
Tris in some broth recipes may be considered a superstitious procedure
without much scientific merit. See also
Agar plate Salvador Luria
SOC medium—another widely used medium for culture of Escherichia coli in
molecular biology work References