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Unformatted text preview: J OURNAL OF BACTERIOLOGY, Dec. 2007, p. 8746–8749 Vol. 189, No. 23 0021-9193/07/$08.00 0 doi:10.1128/JB.01368-07 Copyright © 2007, American Society for Microbiology. All Rights Reserved. Escherichia coli Physiology in Luria-Bertani Broth Guennadi Sezonov,* Danie`le Joseleau-Petit, and Richard D’Ari Institut Jacques Monod, CNRS, Universite´ Paris 6, Universite´ Paris 7, F-75251 Paris Cedex 05, France Received 22 August 2007/Accepted 14 September 2007 Luria-Bertani broth supports Escherichia coli growth to an optical density at 600 nm (OD 600 ) of 7. Surpris- ingly, however, steady-state growth ceases at an OD 600 of 0.3, when the growth rate slows down and cell mass decreases. Growth stops for lack of a utilizable carbon source. The carbon sources for E . coli in Luria-Bertani broth are catabolizable amino acids, not sugars. The widely used rich medium called Luria-Bertani broth is popular with bacteriologists because it permits fast growth and good growth yields for many species. The recipe for Luria- Bertani broth is as follows. Combine 10 g of tryptone, 5 g of yeast extract, 10 g of NaCl, and 1 liter of distilled water; adjust the pH to 7.0 with 1 N NaOH; and autoclave the mixture for 25 min at 120°C. The tryptone used is a pancreatic digest of casein from cow’s milk, and the yeast extract used is an autodigest of Saccharomyces cerevisiae . Dehydrated Luria-Bertani broth with the above composition is sold by Difco and called LB Broth, Miller; with 5 g/liter NaCl it is called LB Broth, Lennox. A great deal of work on Escherichia coli physiology has been carried out with cultures in steady-state growth. One of the principal advantages of this is the extreme reproducibility of the physiological state of the bacteria; during steady-state growth in a given medium, a given strain will always achieve the same state. It is reached after a variable lag period and at low cell density, such that the quantity of nutrients removed from the medium is negligible and the concentration of ex- creted compounds does not affect growth. During steady-state growth, by definition, the following criteria must hold. (i) All intrinsic parameters of the cells remain constant. Measured as population averages, these include the mean volume, density, and macromolecular composition of the cells. (ii) All extrinsic parameters increase exponentially with precisely the same dou- bling time. These include the optical density of the culture, the number of cells per milliliter, the amount of protein per mil- liliter, the amount of RNA per milliliter, the amount of DNA per milliliter, etc. (iii) The composition, pH, and temperature of the medium all remain constant within the cells’ detection limits. Cultures in steady state exhibit balanced exponential growth (3)....
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