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Acute combination of nitrogen and light induces the simulta-neous accumulation of astaxanthin and lutein in continuous cultures of the microalga Chromochloris zofingiensis

ABSTRACT: Carotenoids are essential pigments in photosynthesis and other physiological processes, present in various organisms. Microalgae are considered an important natural source for the commercial production of some of these compounds. The accumulation of the carotenoids astaxanthin and lutein in response to nitrogen and light availability has been optimized in continuous photoautotrophic cultures of Chromochloris zofingiensis. Astaxanthin cellular content increased significantly as the nitrate concentration in the feed medium decreased, while that of lutein remained largely unchanged. The cellular levels of lutein and astaxanthin were inversely correlated with the nitrogen content of the biomass. Thus, for 4% N in the dry biomass, accumulation of astaxanthin was highest and that of lutein lowest. The opposite was recorded for 9% N. Average irradiance positively affected lutein accumulation at both high and low nitrate, whereas that of astaxanthin did only increase under nitrogen-limiting conditions. An integrated analysis of transcriptomics and carotenoid profiling data provides evidence that the response to nitrogen is more significant than that to light availability, and that a synergy exists between both factors, with enhancement of their individual effects. Regulation appears to be orchestrated at several levels: the expression pattern of cyclases suggests a redirection of lycopene to β-carotene, which is converted into astaxanthin through overexpression of BKT1. In turn, slightly higher lutein values are achieved by altering the α-carotene/lutein ratio, due to upregulation of CYP97A1 and CYP97C, especially under high irradiance conditions. The differential responses of astaxanthin and lutein to nitrogen and light availability could enable the programmed generation of C. zofingiensis biomass in continuous culture with a specific astaxanthin to lutein ratio, through careful adjustment of the nitrate concentration in the feed medium, using light irradiance as a modulator.

ORGANISM(S): Chromochloris zofingiensis

PROVIDER: GSE317028 | GEO | 2026/04/01

REPOSITORIES: GEO

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Project description:While the green microalga, Haematococcus pluvialis, is the best natural producer of astaxanthin, efforts to grow it for astaxanthin production are still limited by its low biomass productivity which subsequently results in lower astaxanthin productivity. Despite new methods of direct strain modification to improve growth and astaxanthin production, the limited understanding of how the astaxanthin biosynthesis pathway is regulated has been a significant roadblock to strain improvement. This work aims to address this knowledge gap by exploring the stress response of H. pluvialis during the transition from heterotrophy to high light conditions. A physical radiation (heavy-ion beam) mutagenesis approach was applied to generate H. pluvialis mutants with a higher cell division rate under heterotrophic conditions. The mutant JWHIB 27-38 that grew 25% faster than the wild type was identified. Mutant JWHIB 27-38 also achieved a 69.61% higher lipid content per cell and 86.17% higher astaxanthin per cell than the wild type under high light stress conditions. A proteomics and phosphoproteomics analysis was conducted with JWHIB 27-38 and the wild type at 0, 48, and 72 h of high light stress to elucidate the mechanisms underlying these phenotypes. Maintained upregulation of chlorophyll biosynthesis pathway proteins and phosphoproteins in mutant JWHIB 27-38 during high light stress, such as glutamate-1-semialdehyde 2,1-aminomutase (GSAM) and coproporphyrinogen oxidase (CPOX), may support continued chlorophyll biosynthesis which can allow cells to adapt to high light conditions. Upregulation of fatty acid biosynthetic proteins such as biotin carboxyl carrier protein (BCCP) and 3-ketoacyl-CoA synthase (KCS) in mutant JWHIB 27-38 suggests that carbon is favored toward lipid accumulation. Increased lipid content, along with upregulation of the key astaxanthin biosynthesis protein, phytoene synthase (PSY), may enable the higher astaxanthin content in mutant JWHIB 27-38. Additionally, upregulation of a putative astaxanthin-trafficking protein, AstaP, likely enables the mutant to traffic more astaxanthin to the cell periphery as part of its stress response. These and other significantly differentially expressed proteins may provide promising targets for future strain engineering work to improve astaxanthin productivity.

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Acute combination of nitrogen and light induces the simulta-neous accumulation of astaxanthin and lutein in continuous cultures of the microalga Chromochloris zofingiensis

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