Fermentation Process Optimization And Kinetic Studies Of The Novel Antifungal Substance CF66I

According to the statistics studies, more than 80% of the plant diseases are caused by the fungus.Usually fungi not only destroy the plants, but also produce mycotoxins that are harmful to human health. At present, chemical fungicides are mainly used for the prevention of fungi-related plant diseases, however, research and development of biological prevention and controlling are of great importance.Recently, a strain named as CF-66 with strong antifungal activity has been isolated from the compost samples, which strongly inhibits the growth of many plant pathogens such as Rhizoctonia solani. Antifungal substance CF66I was isolated from strain CF-66 and was proved to be a novel antibacterial compound. In this work, the batch fermentation process optimization was carried out, and kinetic models were developed.Shaking-flask culture of Burkholderia cepacia CF-66 was firstly performed and studied. The suitable age of the seed was determined to be 18 h and the proper broth volume was 90 ml in 250 ml flask. Medium for batch fermentation was optimized by fractional factorial design, the method of steepest ascent and central composite design.Batch fermentation was further conducted in 3.7 L fermentation tank. It was found that high K_La level was disadvantageous to the cell growth and the CF66I production at the beginning of the fermentation. The K_La value was optimized at 121.2 h^-1. The dissolved oxygen concentration (DO) was optimized at 15% air saturation. Consequently, a two-stage oxygen supply control strategy was applied in which K.La value was fixed at 121 h^-1 at the first 28 h, then the DO value was changed to 15% air saturation by varying the stirring speeds and the aeration rate until the end of the fermentation to increase the production of CF66I. By applying this strategy in batch fermentaion, the maximal antifungal activity of CF66I had an improvement and reached 3.374 u/ml, compared to those of constant operations (2.215 u/ml and 2.949 u/ml).The pH and the temperatures were found to be important for the production of CF66I. The pH control strategy was controlling pH value at 6.0 at the first 12 h and then left the value without control for the second 12 h, following by maintaining the pH value at 8.0 till the end of the fermentation. When batch fermentation experiment was conducted using the optimized culturing strategy, the antifungal activity was increased to 2.866 u/ml, while in the constant pH fermentation process the maximal was determined to be 2.722 u/ml. The temperature...