Introduction to bioreactors of shake-flask inocula leads to development of oxidative stress in Aspergillus niger
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Inoculation of bioreactors with shake-flask cultures present the organism with an immediate shift from an environment with little O2 to one in which O2 is typically at 100% saturation. The inoculation of such shake-flasks cultures into bioreactors sparged with 1 vvm air or 1 vvm air/O2 mix i.e. 50% O2 enrichment is an oxidatively stressful event, as judged by immediate increases in the intracellular concentrations of superoxide anion radical (O2·−) (from 4,600 to 11,600 RLU mg DCW−1 and 5,500 to 23,000 RLU mg DCW−1 respectively) and changes in the activities of the major antioxidant enzymes superoxide dismutase and catalase in all cultures. There are further effects on metabolic indices, particularly decreased nutrient consumption in oxygenated cultures (from 0.16 to 0.12 g starch g DCW h−1) and decreased protein production, indicating that inoculation of the bioreactor exerts a global burden on the cellular metabolic networks.
KeywordsFilamentous fungi Lag phase Oxidative stress Oxygen enrichment
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