Abstract
Gibberellic acid (GA(3)) is a natural plant growth hormone that has been widely used in agriculture and horticulture. To obtain higher GA(3) producing strains, the method of screening the strains for resistance to simvastatin was used after treatment with nitrosoguanidine (NTG) and gamma rays. The rationale for the strategy was that mutants showing simvastatin resistance were likely to be high GA(3) producers, as their activity of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is relatively more effective. GA(3) yield of mutant S109 increased by 14.2% than that of the original strain. The GA(3) production ability in mutant S109 remained relatively stable after ten generations. With the addition of 0.4 g glycerol on the 5th day during the fermentation process in Erlenmeyer flask, maximum GA(3) production of 2.7 g/L was achieved by this mutant, exhibiting 28.6% increase compared with original strain. Furthermore, we also achieved 2.8 g/L GA(3) and had a 33.3% increase with addition 20 g glycerol on the 5th day during the fermentation process in a 5-L bioreactor. Our results indicated efficient GA(3) production could be achieved on the condition that the supply of glycerol at the suitable conditions. This study would lay a foundation for industrial production of GA(3).