Abstract
BackgroundMonascus pigments are widely used in the food and pharmaceutical industries due to their safety to human health. Our previous study found that glucose concentration induced extracellular oxidoreduction potential (ORP) changes could influence extracellular water-soluble yellow pigment production by Monascus ruber CGMCC 10910 in submerged fermentation. In this study, H2O2 and dithiothreitol (DTT) were used to change the oxidoreduction potential for investigating the effects of oxidative or reductive substances on Monascus yellow pigment production by Monascus ruber CGMCC 10910.ResultsThe extracellular ORP could be controlled by H2O2 and DTT. Both cell growth and extracellular water-soluble yellow pigment production were enhanced under H2O2-induced oxidative (HIO) conditions and were inhibited under dithiothreitol-induced reductive conditions. By optimizing the amount of H2O2 added and the timing of the addition, the yield of extracellular water-soluble yellow pigments significantly increased and reached a maximum of 209 AU, when 10 mM H2O2 was added on the 3rd day of fermentation with M. ruber CGMCC 10910. Under HIO conditions, the ratio of NADH/NAD+ was much lower than that in the control group, and the expression levels of relative pigment biosynthesis genes were up-regulated; moreover, the activity of glucose-6-phosphate dehydrogenase (G6PDH) was increased while 6-phosphofructokinase (PFK) activity was inhibited.ConclusionsOxidative conditions induced by H2O2 increased water-soluble yellow pigment accumulation via up-regulation of the expression levels of relative genes and by increasing the precursors of pigment biosynthesis through redirection of metabolic flux. In contrast, reductive conditions induced by dithiothreitol inhibited yellow pigment accumulation. This experiment provides a potential strategy for improving the production of Monascus yellow pigments.
Highlights
Monascus pigments are widely used in the food and pharmaceutical industries due to their safety to human health
The results showed that lower amounts of H2O2 could promote cell growth while higher amounts of H2O2 had an inhibitory effect on cell growth (Fig. 1a)
glucose-6-phosphate dehydrogenase (G6PDH) activity under oxidative conditions was higher than that of the control group (Fig. 6b), which indicated that the metabolites involved in phosphate pathway (PPP) under oxidative condition were significantly up-regulated. These results showed that M. ruber CGMCC 10910 redirects its metabolic flux from the glycolysis pathway to the PPP, and more energy (NADPH) could be produced for polyketide and lipid biosynthesis [28, 35, 36], which is consistent with reported studies that show that metabolic flux was altered from the glycolysis pathway to the PPP, and an abundance of precursors were available for validamycin A biosynthesis in Streptomyces hygroscopicus 5008 fermentation in response to various oxidant treatments [38, 39]
Summary
Monascus pigments are widely used in the food and pharmaceutical industries due to their safety to human health. Our previous study found that glucose concentration induced extracellular oxidoreduction potential (ORP) changes could influence extracellular water-soluble yellow pigment production by Monascus ruber CGMCC 10910 in submerged fermentation. In this study, H2O2 and dithiothreitol (DTT) were used to change the oxidoreduction potential for investigating the effects of oxidative or reductive substances on Monascus yellow pigment production by Monascus ruber CGMCC 10910. Chen has shown that both extracellular and intracellular yellow pigments are the main pigments produced during long periods of high cell density culturing by Monascus anka [19]. Our previous studies found that extracellular water-soluble yellow pigments can be produced by M. ruber CGMCC 10910 using high glucose concentrations with low oxidoreduction potential (ORP) [20, 21]. The pigment yield and glucose utilization was still low
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