Application of oxygen vectors to Aspergillus terreus cultivation

Research was undertaken to examine the effects of adding an oxygen carrier (n-dodecane, n-tetradecane, or n-hexadecane) on lovastatin production by Aspergillus terreus in both shaking-flask and 5-l fermentor cultivations. In the shaking-flask cultivation, an addition of 2.5% (w/v) n-dodecane to the medium gave about a 1.4-fold increase (0.51 g/l) in lovastatin production. This improvement was related to morphological changes in the fungal cells, and resulted mainly from the formation of small, uniform, compact pellets of A. terreus. In contrast, in the 5-l fermentor cultivation, the lovastatin production was only one-ninth of that achieved without n-dodecane addition independent of the pellet density. This adverse effect of adding the oxygen carrier to the medium was attributed to an uncontrolled, high dissolved oxygen level (higher than 60%) which resulted in unfavorable morphological changes and the formation of star-like pellets. However, when this dosage of n-dodecane was added 24 h after the start of the 5-l fermentor cultivation, lovastatin production was further enhanced due to its foam suppressing activity in the fungal fermentation.