One of the major challenges facing large-scale production of secondary metabolites in culture is the tendency of the cultured cells to accumulate the biosynthetic products intracellularly. There have been attempts to permeabilize cell walls of the cultured cells to enable release. This has been tried with DMSO, making media acidic and even with physical treatments such as ultrasonication and short electrical pulses. An ideal permeabilization technique has to be reversible and should not affect cell viability.

Product Harvest from Media

Periodic removal of secondary metabolites accumulated in media is necessary to prevent unwanted degradation of products or feedback inhibition of the proceeding biosynthesis. Several extraction techniques like two-phase liquid cultures are in use. Here an additional immiscible liquid acting as a solvent for the formed metabolite is added to the culture liquid by which it goes into solution into this liquid. Being immiscible it can easily be separated and product harvested. For example, C. ledgeriana cultures were treated with Amberlite XAD-7—a resin, to selectively phase out formed anthraquinones in culture. Such periodic removal by solubilizing it in the second phase enhances further production. Several such newer immiscible liquid phases such as dimethyl siloxane are being experimented upon.