ROS Induce β-Carotene Biosynthesis Caused by Changes of Photosynthesis Efficiency and Energy Metabolism in Dunaliella salina Under Stress Conditions

Abstract

The unicellular alga Dunaliella salina is regarded as a promising cell factory for the commercial production of β-carotene due to its high yield of carotenoids. However, the underlying mechanism of β-carotene accumulation is still unclear. In this study, the regulatory mechanism of β-carotene accumulation in D. salina under stress conditions was investigated. Our results indicated that there is a significant positive correlation between the cellular ROS level and β-carotene content, and the maximum quantum efficiency (Fv/Fm) of PSII is negatively correlated with β-carotene content under stress conditions. The increase of ROS was found to be coupled with the inhibition of Fv/Fm of PSII in D. salina under stress conditions. Furthermore, transcriptomic analysis of the cells cultivated with H2O2 supplementation showed that the major differentially expressed genes involved in β-carotene metabolism were upregulated, whereas the genes involved in photosynthesis were downregulated. These results indicated that ROS induce β-carotene accumulation in D. salina through fine-tuning genes which were involved in photosynthesis and β-carotene biosynthesis. Our study provided a better understanding of the regulatory mechanism involved in β-carotene accumulation in D. salina, which might be useful for overaccumulation of carotenoids and other valuable compounds in other microalgae.

Co-Expression of Lipid Transporters Simultaneously Enhances Oil and Starch Accumulation in the Green Microalga Chlamydomonas reinhardtii under Nitrogen Starvation

“…The cell-permeable fluorogenic probe 2′,7′-dichlorodihydrofluorescein diacetate (DCFH-DA, Beyotime, Shanghai, China) was used to determine the ROS levels as previously described [ 25 , 30 ]. Briefly, the Chlamydomonas cells (20 × 10 6 cells mL −1 ) were collected by centrifugation, washed once with 1 × PBS buffer (0.01 M), and resuspended in 500 μL 1 × PBS buffer containing 0.5 μL DCFH-DA.…”

“…Briefly, the cell culture (5.0 mL) was filtered using preweighted 47 mm diameter Whatman GF/C filters and dried at 80 °C for 24 h in an incubator. The biomass of the algal cells was then gravimetrically measured as previously described [ 25 , 30 ].…”

Enhanced accumulation of oil through co-expression of fatty acid and ABC transporters in Chlamydomonas under standard growth conditions

“…Biomass was determined by dry weight measurements as previously described [ 46 , 52 ]. Briefly, the same concentration of cells (2.0 × 10 6 cells/mL) were inoculated and cultivated.…”

“…The maximal quantum conversion efficiency of PS II ( F v /F m ) of algal cells was measured by pulse amplitude-modulated (PAM) fluorometry (Water-PAM WALZ, Germany) as previously described [ 52 , 53 ]. Briefly, the cells were dark-adapted for 10 min inside the spectrophotometer before the measurement of the maximal PS II quantum yield.…”

Productivity and nutrient removal by the microalga Chlamydopodium fusiforme grown outdoors in BG-11 and piggery wastewater

“…These findings are in line with what was observed in the cultures grown in PWW, which exhibited values of V J lower than the ones found on BG-11, as already discussed in paragraph 4.1. In particular, the V J parameter reflects the level of reduction of the plastoquinone electron acceptors, and its increase may reveal the occurrence of oxidative stress activating defensive strategies to counteract the effect of ROS generation (Carol and Kuntz, 2001;Xi et al, 2021). In photosynthetic microorganisms, carotenoid synthesis is one of the main processes involved in these defense mechanisms, and it may imply the increase of both specific antioxidant carotenoids and total carotenoids content (Masojidek et al, 1999;Masojidek et al, 2004;Shi et al, 2020).…”