Multilevel Regulation of Carotenoid Synthesis by Light and Active Oxygen in Blakeslea trispora

Transcriptomic Analysis Reveals the Potential Mechanisms for Improving Carotenoid Production in Rhodosporidium toruloides Z11 under Light Stress

Carotenoids, as a type of tetraterpene compound, have been widely used in food, medical, and health areas owing to their antioxidant, immune enhancement, and disease risk reduction effects. Rhodosporidium toruloides is a promising oleaginous red yeast that can industrially synthesize carotenoids. In this study, the effects of different light exposure times and intervals on carotenoid production by R. toruloides Z11 were first investigated. Results showed that a higher carotenoid content (1.29 mg/g) can be achieved when R. toruloides Z11 was exposed to light for 12 h per day, which was increased by 1.98 times compared with that of dark cultivation. Transcriptome profiling revealed that light stress could effectively promote the gene expression levels of GGPS1 and AL1 in the carotenoid biosynthesis pathway and phr in the DNA photolysis pathway of R. toruloides. This work will provide a molecular foundation to further improve the production efficiency of carotenoids by genetic engineering.

Light irradiation changes the regulation pattern of BtCrgA on carotenogenesis in Blakeslea trispora

CrgA has been shown to be a negative regulator of carotenogenesis in some filamentous fungi, while light irradiation is an inducible environmental factor for carotenoid biosynthesis. To clarify the relationship between CrgA and light-inducible carotenogenesis in Blakeslea trispora, the cis-acting elements of the btcrgA promoter region were investigated, followed by the analyses of correlation between the expression of btcrgA and carotenoid structural genes under different irradiation conditions. A variety of cis-acting elements associated with light response was observed in the promoter region of btcrgA, and transcription of btcrgA and carotenoid structural genes under different irradiation conditions was induced by white light with a clear correlation. Then, RNA interference and overexpression of btcrgA were performed to investigate their effects on carotenogenesis at different levels under irradiation and darkness. The analyses of transcription and enzyme activities of carotenoid structural gene, and accumulation of carotenoids among btcrgA-interfered, btcrgA-overexpressed, and wild-type strains under irradiation and darkness indicate that btcrgA negatively regulates the synthesis of carotenoid in darkness, while promotes the carotenogenesis under irradiation regardless of reduced or overexpression of btcrgA .

Physiological changes of microalga Dunaliella parva under the treatment of PEG, CaCl2

Carotenoids are antioxidants, which reduce various chronic diseases of human, and have many industrial applications. The halophilic Dunaliella parva (D. parva) is rich in carotenoids. The compounds CaCl2 and PEG are the popular metabolic enhancers. To further enhance carotenogenesis, D. parva was treated with two compounds polyethylene glycol (PEG) and CaCl2. Application of CaCl2 and PEG enhanced the carotenoids contents and the antioxidant activities of carotenoids compared to control group (no treatment of CaCl2 or PEG). The highest carotenoids contents were obtained by treating D. parva with 40 ppm CaCl2 (3.11 mg/g dry weight, DW) and 80 ppm PEG (2.78 mg/g DW) compared with control group (1.96 mg/g DW). When D. parva was treated with 40 ppm CaCl2 and 80 ppm PEG, protein contents reached the highest values (90.28 mg/g DW and 89.57 mg/g DW) compared to that of control group (73.42 mg/g DW). The antioxidant activities of carotenoids samples were determined. Generally, the antioxidant activities of carotenoids from D. parva treated with PEG and CaCl2 were superior to that of control group. The antioxidant activities of carotenoids mainly contained reducing power, hydroxyl radical scavenging activity and superoxide radical scavenging activity. The reducing powers of carotenoids extracts from 20 ppm CaCl2 group (2.07%/mg carotenoids) and 120 ppm PEG group (1.59%/mg carotenoids) were significantly higher than that of control group (<1.25%/mg carotenoids). The superoxide radical scavenging activities of carotenoids extracts from 40 ppm CaCl2 group (70.33%/mg carotenoids) and 80 ppm PEG group (65.94%/mg carotenoids) were significantly higher than that of control group (<55%/mg carotenoids). This paper laid a foundation for massive accumulation of carotenoids in microalga D. parva.

Effects of Blue Light on Hypocrellin A Production in Shiraia Mycelium Cultures

Blue light is a crucial environmental cue for fungi. Hypocrellin A (HA) is a photoactive perylenequinone from Shiraia with strong antimicrobial and anticancer properties. In this study, effects of the illumination of blue light-emitting diode (LED) at 470 nm on Shiraia sp. S8 was investigated. Blue light at 50-200 lx and 4-6 h/day could enhance HA content in the mycelia, but suppress it at 300-400 lx or with longer exposure (8-24 h/day). The intermittent blue light (6 h/day) at 200 lx not only enhanced the fungal conidiation, but stimulated HA production without any growth retardation. The generation of fungal reactive oxygen species (ROS) was induced to up-regulate HA biosynthetic gene expressions. When the culture was maintained under the intermittent blue light for 8 days, HA production reached 242.76 mg/L, 2.27-fold of the dark control. On the other hand, both the degradation of HA and down-regulation of HA biosynthetic genes occurred under long exposure time (8-24 h/day), leading to the suppression of HA production. These results provide a basis for understanding the regulation of blue light on the biosynthesis of fungal photoactivated perylenequinones, and the application of a novel light elicitation to Shiraia mycelium cultures for enhanced HA production.

Biotechnological advances for improving natural pigment production: a state-of-the-art review

In current years, natural pigments are facing a fast-growing global market due to the increase of people's awareness of health and the discovery of novel pharmacological effects of various natural pigments, e.g., carotenoids, flavonoids, and curcuminoids. However, the traditional production approaches are source-dependent and generally subject to the low contents of target pigment compounds. In order to scale-up industrial production, many efforts have been devoted to increasing pigment production from natural producers, via development of both in vitro plant cell/tissue culture systems, as well as optimization of microbial cultivation approaches. Moreover, synthetic biology has opened the door for heterologous biosynthesis of pigments via design and re-construction of novel biological modules as well as biological systems in bio-platforms. In this review, the innovative methods and strategies for optimization and engineering of both native and heterologous producers of natural pigments are comprehensively summarized. Current progress in the production of several representative high-value natural pigments is also presented; and the remaining challenges and future perspectives are discussed.