A proposed biochemical mechanism for citric acid accumulation by Aspergillus niger Yang No. 2 growing in solid state fermentation |
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Authors: | Leangon S Maddox IS Brooks JD |
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Institution: | (1) College of Sciences, Massey University, Palmerston North, New Zealand;(2) Present address: Department of Microbiology, Burapha University, Chonburi, Thailand |
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Abstract: | Aspergillus niger Yang No. 2 and its mutant strain SL1 were grown in solid state fermentation. Samples were taken after 2, 4 and 6 days of incubation and the mycelia were analysed for their intracellular concentrations of some organic acids and adenylates and the activities of selected enzymes. Strain Yang No. 2 contained high concentrations of citrate with very little oxalate, while strain SL1 contained lower concentrations of citrate but considerably higher concentrations of oxalate. As the fermentation proceeded, strain Yang No. 2 showed a much higher ratio of ATP:AMP than did strain SL1. In addition, the enzyme ATP:citrate lyase became undetectable during citrate accumulation in strain Yang No. 2, while its activity remained high during oxalate accumulation in strain SL1. It is proposed that citrate accumulation by strain Yang No. 2 during solid state fermentation is due to blockage of its metabolism in the mitochondrion via inhibition of isocitrate dehydrogenase by the high ATP:AMP ratio, and in the cytosol by repression of ATP:citrate lyase activity. |
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Keywords: | Adenylates Aspergillus niger ATP:citrate lyase citric acid oxalic acid |
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