Accumulation of phytoene and astaxanthin and related genes expression in Haematococcus pluvialis under sodium acetate stress

Abstract

Phytoene and astaxanthin are 2 important carotenoids in the green alga Haematococcus pluvialis. Under environmental stress, the synthesis of phytoene in H. pluvialis increases significantly, and phytoene is converted to astaxanthin through enzymatic catalysis. This paper analyzes the relationship between astaxanthin and phytoene accumulation in carotenoid synthesis pathways under different concentrations of sodium acetate (NaAc) by high-performance liquid chromatography. The highest concentrations of phytoene and astaxanthin were observed at the NaAc concentration of 6 g l-1 on the 12th day of induction. The highest astaxanthin concentration achieved was 2.26 ± 0.28%. Therefore, we concluded that 6 g l-1 NaAc and induction for 12 d provided the optimal inducing conditions for astaxanthin accumulation in H. pluvialis. psy, pds, lcyB, β-carotene ketolase crtw, and crtz, which are genes related to phytoene and astaxanthin synthesis, were cloned and studied at the transcriptional level. crtw and crtz were continuously up-regulated since the first day of induction, while psy, pds, and lcyB were continuously up-regulated starting on the 3rd day of induction. These findings are important for enhancing our understanding of the mechanism of accumulation of phytoene and astaxanthin in H. pluvialis and provide a foundation for identifying the induction conditions necessary for optimizing astaxanthin production and increasing astaxanthin yields.

Haematococcus pluvialis Accumulated Lipid and Astaxanthin in a Moderate and Sustainable Way by the Self-Protection Mechanism of Salicylic Acid Under Sodium Acetate Stress

“…The downregulation of fatty acid biosynthesis-related genes, especially the unsaturated fatty acid biosynthesis genes, from Stage SAHS_1 to SAHS_48 demonstrated that exogenous SA played a role in providing a protection mechanism for H. pluvialis cells against the abiotic stress caused by high NaAC. These results were consistent with the astaxanthin, and fatty acid accumulation speculated to stimulate the self-protective metabolism as a defense against the high concentration sodium acetate stress (Cong et al, 2020).…”

“…They also demonstrated in another study that the transcriptional expression levels of eight carotenoid genes in H. pluvialis were all downregulated in the first 12 h (except BKT and PDS genes), follow SA25 treatment, and were less than 2.5-fold in comparison with Control follow SA25 treatment in 2-day cultivation (except PDS gene) (Gao et al, 2012b). The phytoene and astaxanthin biosynthesis-related genes were studied at the transcript level under NaAC stress by Cong et al (2020), who reported that CrtW and CrtZ, the two key enzymes involved in astaxanthin biosynthesis, were continuously upregulated since the 1st day of induction, while expression levels of PSY, PDS, and LCYB genes were continuously upregulated ever since the 3rd day of induction. He et al (2018) conducted systemic transcriptome analysis about three variables, including light, acetate, and Fe 2+ , to explore the molecular mechanism of astaxanthin accumulation in the red-cell stage of H. pluvialis.…”

“…Various carbon sources have been studied for mixotrophic or heterotrophic cultivation of H. pluvialis, including acetate, glucose, glycerol, rice straw hydrolyzates, and organic-rich wastewaters (Leite et al, 2015;Gupta et al, 2019). H. pluvialis can also utilize exogenous organic carbon substrates (Kobayashi et al, 1992), and sodium acetate (NaAC) was considered to significantly accelerate cell growth or astaxanthin accumulation (Kobayashi et al, 1993;Orosa et al, 2001;Tolga et al, 2010;Pang et al, 2019;Zhang et al, 2019;Cong et al, 2020). In H. pluvialis, exogenous NaAC increases respiratory rates and suppresses photosynthetic activity in the cells (Zhang et al, 2019).…”

“…In H. pluvialis, exogenous NaAC increases respiratory rates and suppresses photosynthetic activity in the cells (Zhang et al, 2019). It can be used as an effective carbon source, providing energy for the biosynthesis of astaxanthin and fatty acids (Cong et al, 2020;Oslan et al, 2021;Wang et al, 2021;Zhao et al, 2021). NaAC can be utilized by the tricarboxylic acid cycle to control the flux of carbon.…”

Sequential Continuous Mixotrophic and Phototrophic Cultivation Might Be a Cost-Effective Strategy for Astaxanthin Production From the Microalga Haematococcus lacustris

“…Although it is noteworthy that acetate at higher concentrations could be toxic to the cells and adversely affect their growth ( De Swaaf et al, 2003 ), in the presence of low concentrations of Ac, various microalgae can grow well. Various studies also reported the utilization of Ac to not only enhance the growth of green cells but also induce the encystment of H. lacustris ( Cifuentes et al, 2003 ; Cong et al, 2020 ). In the present study, microscopic observations showed that cells did not form cysts when 5 mM Ac was added into the medium in the initial days of cultivation for batch experiments.…”