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AIM - Auto Induction Medium

Auto Induction Media (AIM) have been formulated to grow IPTG-inducible expression strains, initially without induction, and then to induce production of target protein automatically, usually near saturation at high cell density. A limited concentration of glucose is metabolized preferentially during growth, which prevents uptake of lactose until the glucose is depleted, usually in mid to late log phase. As the glucose is depleted, lactose can be taken up and converted by β-galactosidase to the inducer allolactose. Allolactose causes release of lac repressor from its specific binding sites in the DNA and thereby induces expression of T7 RNA polymerase from the lacUV5 promoter and unblocks T7lac promoters, allowing expression of target proteins by T7 RNA polymerase.


With AIM media a high density cell growth is followed by a spontaneous induction of protein expression. There is no need to monitor the cell density and there is no conventional induction with IPTG.  The principle of AIM media is based on carbon sources in the medium that are metabolized differentially to promote high density cell growth and automatically induce protein expression from lac promoters.

Parallel growth of many non-induced or auto-induced cultures is feasible because cultures are simply inoculated and grown to saturation.  This is a great convenience and simplifies manual or automated induction and analysis of multiple clones compared to conventional IPTG induction, which requires monitoring growth of each culture and adding inducer at the proper stage of growth.

The components used in AIM media can be grouped in five functional clusters of components.

Nitrogen Source
Tryptone and Yeast Extract are present as a general nitrogen source for growth and protein expression.  Both are excellent sources for nitrogen and additionally Yeast Extract provides B-type vitamins, carbohydrates and growth factors.  Due to different demands for nitrogen by various cellines for both growth and protein production Formedium™has developed four different types of AIM media based upon a different quantity and ratio in Tryptone and Yeast Extract.

Within our AIM range are AIM-LB Broth, AIM-2YT Broth, AIM-Terrific Broth and AIM-Super Broth.  For more detailed information about  concentrations and quantities look at the different product descriptions.  For the researcher it is up to decide which type of AIM medium will supports growth and yield at maximum.

Additionally Ammonium Sulphate (NH4)2SO4 is added to the medium for increased protein synthesis.

Carbon Source
In AIM media D-Glucose and α-Lactose are present in a blend optimized for tightly regulated uninduced growth to high cell density followed by high-level induction due to the depletion of glucose and subsequently the conversion of lactose in allolactose.

In AIM media a phosphate buffer is present to reduce a drop in pH because of glucose metabolism.

Magnesium Sulphate (MgSO4)
High density growth in complex media is often limited by lack of Magnesium Sulphate.  Extra is added to the medium to achieve high saturation cell density.

Trace Elements
Growth to high cell density and high yield protein expression might require the addition of an extra addition of trace elements.  Although these elements are present in complex media based on Tryptone and Yeast Extract an extra addition of nine different trace elements plus iron provides amounts sufficient to saturate substantial production of target protein.  CaCl2, MnSO4, ZnSO4, CoCl2, CuSO4, NiCl2, NaMoO4, Na2SeO3 and FeCl3 are supplementary to the AIM media including trace elements.

AIM media can be supplied with or without the extra addition of trace metals.

The AIM or Auto Induction Media as produced and supplied by Formedium™ are based on the work of F. William Studier, Protein Production by Auto-Induction in High-Density Shaking Cultures. Brookhaven National Laboratory, Upton, NY 11973

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