| A strain of Penicillium sp. PT95 was isolated from soil sample collected close to Fenyang, Shanxi Province. The strain can form abundant orange, sand-shaped sclerotia in which carotenoid was accumulated. By morphological observation and RAPD typing, PT95 strain had been identified to P. thomii series. The aim of this study was to determine how high and low oxidative stress growth conditions affected carotenoid biosynthesis and sclerotial differentiation of strain PT95. In addition, the effects of exogenous P-carotene on sclerotial biomass, carotenoid yield and lipid peroxidation of this fungus were examined.Under the growth condition of high (light) oxidative stress and low (dark) oxidative stress, the differentiation and development of PT95 strain in Georgiou agar medium and liquid medium was similar. PT95 initially covered the Petri dish with mycelia at 3d. Thereafter, sclerotia appeared on top of the mycelium and their development was completed in three main stages: on Day 6, mycelia formed loosely bound, intertwined, white hyphal branches, called sclerotial initials (SI). Then, SI progressively developed to full-size, light brown, compact sclerotia, designated as early-, mid- and late-developed sclerotia (SD) at Days 8, 10 and 12, respectively. Mature sclerotia (SM) were formed on Day 14. SM sclerotia were orange, densely accumulated with carotenoids. SD and SM sclerotia secreted droplets called exudates. The differentiation and development of PT95 strain in CA medium was similar to that in Georgiou agar medium. The growth period of PT95 strain in CA medium was longer than that in Georgiou agar medium.When β-carotene (in 0.1% v/v THF) was added as sole carbon source, it did not support fungal growth.The condition of differentiation was changed after supplemented with exogenous P-carotene in the medium. The time of both exudates and sclerotia initials of PT95 strain were delayed. The higher the concentration ofexogenous P-carotene was, the longer the time of delay. But the time of sclerotial maturation was not changed.The influence of exogenous P-carotene and different oxidative stress growth conditions on sclerotia biomass and carotenoid yield of PT95 strain were studied. The growth condition at high oxidative stress favored carotenoid accumulation of PT95. The sclerotia biomass and carotenoid yield was 21.4% and 165% higher respectively at high than at low oxidative stress. But in CA medium, the sclerotia biomass was higher than Georgiou agar medium at high or low oxidative stress. It was 1.4 and 1.2 fold respectively. The content of carontenoid and carotenoid yield were lower than that in CA medium.The effect of exogenous (3-carotene on sclerotial differentiation of PT95 strain was concentration-dependent, resulting in a gradual increase in the biomass of produced matured sclerotia. However, when plotting the carotenoid content versus the concentration of exogenous P-carotene in medium, a negative linear relation was found. It was illustrated that exogenous p-carotene could depress the carotenoid metabolism of PT95 strain. The higher the concentration of exogenous P-carotene was, the lower the carotenoid content.The result may suggest the following possible conclusion. In unfavorable conditions PT95 strain differentiates forming sclerotia for long-term survival. Carotenoid may be produced to counter ROS formation and remedy deficiency of antioxidation. Supplementation of exogenous p-carotene may cause the reduction of carotenoid yield.The lipid peroxidation in colonies of PT95 and PT9, a nonsclerotial mutant strain of PT95, were analyzed. The results showed that with the development of PT95 strain, the level of lipid peroxidation of PT95 was gradual reduced. The degree of reduction was 38% from the 4th day to the 16th day. At the same time, with the development of PT9 strain, the level of lipid peroxidation of PT9 was gradual increased. The degree of increase was 40% from the 4th day to the 16th day. It was indicated that sclerotium was differentiation with...
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