THE GIBBERELLIN FERMENTATION

Gibberellins are a classic example of the production of plant growth regulators by microorganisms. They are important biotechnological products and are increasingly used in agriculture and horticulture. This article intends to assemble information on the history of the identification of gibberellins (GA) and producing microorganisms, especially Gibberella fujikuroi (Saw.) Wr. Furthermore, the biosynthesis of gibberelins through the isoprenoid biosynthetic pathway will be described. The main product of GA biosynthesis in Gibberella fujikuroi is gibberellic acid (GA3), which is formed from GA4 via GA7. Both the amount and the type of gibberellins produced by the fungus are dependent on the genetic constitution of the strain and the fermentation conditions. Mutation and selection for increased product formation are probably the most important factors in improving the yield of gibberellins. Some publications concerning methods of parasexual recombination will also be summarized. Beside strain improvement of wild strains, medium development and appropriate cultivation techniques (batch, fed-batch-, continuous-, and solid state-fermentation) are very important prerequisites for successful economy of gibberellin production. Furthermore, the most important ways of gibberellin recovery and purification are described. Continuing reductions in the costs make gibberellins more attractive for existing applications and open possibilities for further applications of GA3 and some other active gibberellins like GA4, Ga7, and GA9.