EXTRACTIVE FERMENTATION OF GIBBERELLIC-ACID BY GIBBERELLA-FUJIKUROI

Microbial production of metabolites is often limited by product inhibi tion, decomposition or bio-degradation during the process of fermentat ion. if the product can be removed from the broth, e.g. by liquid/liqu id extraction, these losses can be reduced. The production of gibberel lic acid (GA3), a secondary metabolite of the ascomycete Gibberella fu jikuroi, was studied with respect to product inhibition and kinetics o f decomposition under fermentation conditions. A two-fold increase in the yield of GA3 as a result of on-line extraction of the product by p olyalkoxylate (Genapoi 2822) is described. For this extractive ferment ation, a stirred tank fermenter was used. The biomass was separated by cross-flow filtration and recycled. The filtrate was extracted in a m ixer/settler unit with the extraction solvent. The raffinate was recyc led to the fermenter. The influences of product inhibition, chemical d ecomposition of the product and possible bio-degradation on the produc t yield are discussed.