It has been reported that high aeration condition enhanced pigment production but there was no possible explanation why increased pigment production was achieved at high DOT.
This could be due to the active oxygen species i.e singlet oxygen (1O2) which has been reported to regulate the carotenoid biosynthesis. For detailed description you can refer to the following link
http://www.jbc.org/content/270/31/18374.full
A recent Study has indicated that the expression of the gene responsible for carotenoid synthesis is highly dependent on dissolved oxygen. Here is the reference.
Z Naturforsch C. 2011 May-Jun;66(5-6):283-6.
Expression of carotenogenic genes and astaxanthin production in Xanthophyllomyces dendrorhous as a function of oxygen tension.
Wu W1, Lu M, Yu L.
Abstract: This report gives an insight into the specific changes in the transcription of four key carotenogenic genes [encoding geranylgeranyl diphosphate synthase (crtE), phytoene desaturase (crtI), phytoene synthase lycopene cyclase (crtYB), and astaxanthin synthase (ast), respectively] in Xanthophyllomyces dendrorhous cultures, with regard to dissolved oxygen (DO) contents of 10%, 25%, and 40% air saturation, respectively. 25% DO proved to be the most beneficial for yeast growth, transcription of carotenogenic genes, and astaxanthin content.
However the over saturation of oxygen led to oxidation of carotenoids making it colorless.
I agree with Sunil's answer. The protective effect of carotenoids against reactive oxygen species has even been used to boost carotenoid production by engineered yeast via laboratory evolution. Reference:
http://www.sciencedirect.com/science/article/pii/S1096717613001067?via%3Dihub
Well, DO of 25% of saturation does not seem very high for me :-). There are many aerobic bioprocesses, with optimal DO of 30 % of saturation. Otherwise, I agree with the possible scavenging effect of carotenoids in presence of reactive oxygen species.
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