Feedback inhibition existed in lovastatin biosynthesis from Aspergillus terreus. Exogenous lovastatin and other different polyketide antibiotics biosynthesized by polyketide synthase were supplemented to the cultures of A. terreus to investigate their influences on lovastatin production. Supplementing exogenous lovastatin of 100 mg l(-1) at the early stage of fermentation and the fast stage of its biosynthesis resulted in decreases of 76.4% and 20% in final lovastatin production, respectively. However, the fungal cell growth was not affected; the growing cycle was only prolonged in the submerged cultivation. Separate supplementation of the five kinds of polyketide antibiotics such as tylosin, erythromycin, tetracycline, daunorobin, and rifamycin to the cultures resulted in increases of about 20 approximately 25% in the final lovastatin production. Especially, supplementing tylosin of 50 mg l(-1) at the beginning of lovastatin biosynthesis led to the final lovastatin production of 952.7 +/- 24.3 mg l(-1), which was improved by 42% and 22% compared with that produced in the control and the original culture, respectively. These results are helpful to understand the regulations on lovastatin biosynthesis and improve the final desired metabolite contents in many antibiotics production.
Article Highlights• Kinetic parameters of models for predicting xylose, glucose, furfural, acetic acid were obtained • The corn stover during hydrolysis was characterized by FTIR, XRD and SEM techniques • A 2 3 five-level Central Composite Design was used for optimization• The validation of the statistical model indicates good agreement
AbstractThe hydrolysis of corn stover using hydrochloric acid was studied. The kinetic parameters of the mathematical models for predicting the yields of xylose, glucose, furfural and acetic acid were obtained, and the corresponding xylose generation activation energy of 100 kJ/mol was determined. The characterization of corn stover using different techniques during hydrolysis indicated an effective removal of xylan and slight alterations of the structures of cellulose and lignin. A 2 3 five-level central composite design (CCD) was used to develop a statistical model for the optimization of process variables including acid concentration, pretreatment temperature and time. The optimum conditions determined by this model were found to be 108 °C for 80 min with acid concentration of 5.8%. Under these conditions, the maximised results were the following: xylose 19.93 g/L, glucose 1.2 g/L, furfural 1.5 g/L and acetic acid 1.3 g/L. The validation of the model indicated good agreement between the experimental results and the predicted values.
The influences of various carbon sources on fungal morphological changes and lovastatin production were investigated in submerged cultivation of a mutant of Aspergillus terreus. Lactose produced the least biomass (2.3 ± 0.15 gDCW l −1 ); however, the highest maximal specific lovastatin productivity (ρ max ) was obtained. Glycerol achieved the highest lovastatin titer (937.5 ± 12.5 mg l −1 ), while soluble starch resulted in the highest biomass (12.05 ± 0.05 gDCW l −1 ) and the second highest lovastatin titer (501.3 ± 23.4 mg l −1 ). With the carbon source turning to be more easily metabolized, the values of ρ max dropped gradually while the corresponding D p and mean filament ratio rose tardily. The value of ρ max (19.8 mg gDCW −1 d −1 ) was obtained in the presence of lactose while glucose resulted in the least ρ max (3.0 mg gDCW. This led to a 6.6-fold decrease. The corresponding D p and mean filament ratios appeared to reverse the effects, thus producing 1.9 and 3.3-fold increases, respectively. The slowly utilizable carbon sources regulated the lovastatin production through both the inducement of fungal morphology differentiation and the control of metabolic regulation.
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