Photoregulation of carotenoid biosynthesis in Aspergillus giganteus mut. alba

Abstract

Aspergillus glganteus mut. alba, grown in shake culture in the light, accumulated 170 pg/g dry wt. of beta-carotene after 6 days of growth. In darkness, no carotenolds were produced, although growth yields were the same as In Illuminated cultures. A white light Intensity of 50w/m2 gave the maximum amount of beta-carotene. Blue light, but not red light, induced beta-carotene formation. Oxygen was required for photoinduction, but the effect of light was temperature-independent. A light Induction period of 10 h was required for maximum beta-carotene production and this was attained 48 h after illumination. 5-flurouracil (10~4?), actinomycin D (10-7M) and cycloheximide all prevent photoinduction of carotenogenesis indicating that photoregulation is at a transcriptional level.Cell extracts from illuminated culture of A. glganteus mut. alba were able to incorporate radioactivity from mevalonic acid into carotenoids, but no such incorporation was obtained with extracts from dark grown cultures. Enzyme activities increased with culture age up to 4 days, and then decreased. A linear relationship was found between the incorporation of radioactivity into carotenoids and the amount of protein in the cell extract up to the maximum with 5 mg of protein. A rapid rate of increase with time in the incorporation of [2-1AC] mevalonic acid into carotenoids was found up to 1 h at 37 °C and 2 h at 24°C.Oxygen was necessary for phytoene desaturation to beta-carotene, the former being accumulated under anaerobic conditions. Glutathione, HADP, IAD, ATP, were found to be necessary for the incorporation of mevalonic acid into carotenoids, while FAD was needed for lycopene and beta-carotene formation. neither nor NADPH was required.Coupling cell extracts of dark- and light-grown cultures of A. giganteus with dark-grown A. giganteus (which accumulates PPPP), and with Phycomyces blakesleeanus C5 carB10 (-) (a phytoene accumulator) and C9 carR21 (-) (a lycopene accumulator), showed that the enzymes beyond prephytoene pyrophosphate i.e. phytoene sythetase, phytoene dehydrogenase and lycopene cyclase, were totally photoinduced.