LBMedium

LB medium, also known as Luria-Bertani medium, is a nutritionally rich bacterial culture medium commonly used in molecular biology. It supports rapid growth of many non-fastidious bacteria, particularly Escherichia coli, making it a standard choice for routine culturing, cloning, and plasmid propagation.

History and naming: The medium was described by Giuseppe Bertani and Salvador Luria in the 1950s; LB stands for Luria–Bertani. Over the years, several commonly used formulations have appeared, including LB Miller and LB Lennox, which differ mainly in salt content and buffering capacity. LB medium is available as a liquid broth and as a solid agar by incorporating a gelling agent.

Composition (conceptual): LB medium combines a protein-rich nutrient source from tryptone and yeast extract with moderate salt to maintain osmotic balance. These components supply amino acids, nucleotides, vitamins, and carbon sources that support vigorous bacterial growth. Some variants include additional buffering or salts to adjust pH and ionic strength. The solid form is called LB agar.

Uses: LB medium is widely used for routine culturing, plasmid maintenance, and growth of a broad range of non-fastidious bacteria. It is often employed in conjunction with selective agents such as antibiotics when plasmid-bearing strains are selected. It is generally used for preliminary culturing and processing before more specialized growth media are used.

Variants and limitations: While versatile, LB medium is not optimal for all organisms; some bacteria require defined or richer media. It is most effective for organisms that grow well on nutrient-rich, undefined media. Commercial suppliers provide ready-to-use LB formulations with different salt levels and agar concentrations.