Astaxanthin accumulation difference between non-motile cells and akinetes of Haematococcus pluvialis was affected by pyruvate metabolism

Enhancement of astaxanthin accumulation via energy reassignment by removing the flagella of Haematococcus pluvialis

Astaxanthin biosynthesis in Haematococcus pluvialis is driven by energy. However, the effect of the flagella-mediated energy-consuming movement process on astaxanthin accumulation has not been well studied. In this study, the profiles of astaxanthin and NADPH contents in combination with the photosynthetic parameters with or without flagella enabled by pH shock were characterized. The results demonstrated that there was no significant alteration in cell morphology, with the exception of the loss of flagella observed in the pH shock treatment group. In contrast, the astaxanthin content in the flagella removal groups was 62.9%, 62.8% and 91.1% higher than that of the control at 4, 8 and 12 h, respectively. Simultaneously, the increased Y(II) and decreased Y(NO) suggest that cells lacking the flagellar movement process may allocate more energy towards astaxanthin biosynthesis. This finding was verified by NADPH analysis, which revealed higher levels in flagella removal cells. These results provide preliminary insights into the underlying mechanism of astaxanthin accumulation enabled by energy reassignment in movement-lacking cells.

Enhancement of astaxanthin production, recovery, and bio-accessibility in Haematococcus pluvialis through taurine-mediated inhibition of secondary cell wall formation under high light conditions

This study explored the use of taurine in enhancing the production and bio-accessibility of astaxanthin in Haematococcus pluvialis, which typically forms a secondary cell wall hindering astaxanthin extraction. The biomass of taurine-treated group significantly increased by 18%, and astaxanthin yield surged by 34% in comparison to the control group. Without cell disruption, astaxanthin recovery from thin-walled cells in the taurine-treated group, using dimethyl sulfoxide and ethanol as extraction reagents, was 97% and 75%, respectively, which were 30-fold higher than those of thick-walled cells in the control group. Additionally, the cell fragmentation rate increased by 86% in taurine-treated group relative to the control group. Comparative transcriptome analysis identified taurine-induced upregulation of genes involved in the astaxanthin biosynthesis pathway and downregulation of those associated with secondary cell wall synthesis. This study thus offers an innovative taurine-based strategy to enhance astaxanthin production and bio-accessibility while shedding light on the mechanisms driving this process.

Mixotrophy, a more promising culture mode: Multi-faceted elaboration of carbon and energy metabolism mechanisms to optimize microalgae culture

Some mixotrophic microalgae appear to exceed the sum of photoautotrophy and heterotrophy in terms of biomass production. This paper mainly reviews the carbon and energy metabolism of microalgae to reveal the synergistic mechanisms of the mixotrophic mode from multiple aspects. It explains the shortcomings of photoautotrophic and heterotrophic growth, highlighting that the mixotrophic mode is not simply the sum of photoautotrophy and heterotrophy. Specifically, microalgae in mixotrophic mode can be divided into separate parts of photoautotrophic and heterotrophic cultures, and the synergistic parts of photoautotrophic culture enhance aerobic respiration and heterotrophic culture enhance the Calvin cycle. Additionally, this review argues that current deficiencies in mixotrophic culture can be improved by uncovering the synergistic mechanism of the mixotrophic mode, aiming to increase biomass growth and improve quality. This approach will enable the full utilization of advantagesin various fields, and provide research directions for future microalgal culture.

Circadian rhythm promotes the biomass and amylose hyperaccumulation by mixotrophic cultivation of marine microalga Platymonas helgolandica

BACKGROUND

Microalgal starch can be exploited for bioenergy, food, and bioplastics. Production of starch by green algae has been concerned for many years. Currently commonly used methods such as nutrient stress will affect cell growth, thereby inhibiting the production efficiency and quality of starch production. Simpler and more efficient control strategies need to be developed.

RESULT

We proposed a novel regulation method to promote the growth and starch accumulation by a newly isolated Chlorophyta Platymonas helgolandica. By adding exogenous glucose and controlling the appropriate circadian light and dark time, the highest dry weight accumulation 6.53 g L-1 (Light:Dark = 12:12) can be achieved, and the highest starch concentration could reach 3.88 g L-1 (Light:Dark = 6:18). The highest production rate was 0.40 g L-1 d-1 after 9 days of production. And this method helps to improve the ability to produce amylose, with the highest accumulation of 39.79% DW amylose. We also discussed the possible mechanism of this phenomenon through revealing changes in the mRNA levels of key genes.

CONCLUSION

This study provides a new idea to regulate the production of amylose by green algae. For the first time, it is proposed to combine organic carbon source addition and circadian rhythm regulation to increase the starch production from marine green alga. A new starch-producing microalga has been isolated that can efficiently utilize organic matter and grow with or without photosynthesis.

Accumulation of Astaxanthin by Co-fermentation of Spirulina platensis and Recombinant Saccharomyces cerevisiae

This study aimed to explore an effective, simple, and time-saving method for astaxanthin accumulation. Wild-type Saccharomyces cerevisiae as a bioreactor, the SpcrtR gene was first ligated with the signal peptide S to construct pYES2/NT-A-S-SpcrtR plasmid in Saccharomyces cerevisiae. The detection of SDS-PAGE and Western blotting protein proved that SpCRTR was successfully extracellular expressed in Saccharomyces cerevisiae. The target product astaxanthin was produced by co-fermentation of Spirulina platensis and recombinant Saccharomyces cerevisiae. The test results showed that after 18 h of fermentation, the astaxanthin concentration was highest in the mixed fermentation broth with 4% Spirulina platensis and recombinant Saccharomyces cerevisiae, and the content of astaxanthin was 0.25 ± 0.02 μg/mL. In addition, the source of astaxanthin was explored. During the fermentation process of the Saccharomyces cerevisiae strain, SpCRTR enzyme catalyzed the Spirulina platensis canthaxanthin, which almost completely converted into astaxanthin, providing a simple method for astaxanthin synthesis. Compared with culture of Haematococcus pluvialis, this culture route not only shortens culture time, but also eliminates the limitation of the conditions in the culture process.

Multifaceted strategies for economic production of microalgae Haematococcus pluvialis-derived astaxanthin via direct conversion of CO2

Owing to its strong antioxidant properties, astaxanthin has a high market price in the nutraceutical and pharmaceutical fields, and its demand is increasing. Furthermore, with an increase in the demand for green technology, astaxanthin production through direct CO₂ conversion using the autotrophic green microalga Haematococcus pluvialis as a bio-platform has received much attention. Large-scale outdoor cultivation of H. pluvialis using waste CO₂ sources and sunlight can secure sustainability and improve economic efficiency. However, low strain performance, reduced light utilization because of increased cell density, and inefficient transfer of gaseous CO₂ into liquid culture broth hinder its large-scale commercialization of astaxanthin. Herein, we presented a multifaceted strategy, including the development of high-efficiency strains, a culture system for astaxanthin accumulation, and astaxanthin extraction from biomass, for economically producing astaxanthin from H. pluvialis through direct CO₂ conversion. Future perspectives were presented by comparing and analyzing various previous studies conducted using the latest technology.

Transcriptomic and Proteomic Characterizations of the Molecular Response to Blue Light and Salicylic Acid in Haematococcus pluvialis

Haematococcus pluvialis accumulates a large amount of astaxanthin under various stresses, e.g., blue light and salicylic acid (SA). However, the metabolic response of H. pluvialis to blue light and SA is still unclear. We investigate the effects of blue light and SA on the metabolic response in H. pluvialis using both transcriptomic and proteomic sequencing analyses. The largest numbers of differentially expressed proteins (DEPs; 324) and differentially expressed genes (DEGs; 13,555) were identified on day 2 and day 7 of the treatment with blue light irradiation (150 μmol photons m⁻²s⁻¹), respectively. With the addition of SA (2.5 mg/L), a total of 63 DEPs and 11,638 DEGs were revealed on day 2 and day 7, respectively. We further analyzed the molecular response in five metabolic pathways related to astaxanthin synthesis, including the astaxanthin synthesis pathway, the fatty acid synthesis pathway, the heme synthesis pathway, the reactive oxygen species (ROS) clearance pathway, and the cell wall biosynthesis pathway. Results show that blue light causes a significant down-regulation of the expression of key genes involved in astaxanthin synthesis and significantly increases the expression of heme oxygenase, which shows decreased expression by the treatment with SA. Our study provides novel insights into the production of astaxanthin by H. pluvialis treated with blue light and SA.

Unveiling the underlying molecular basis of astaxanthin accumulation in Haematococcus through integrative metabolomic-transcriptomic analysis

Astaxanthin is a valuable and highly demanded ketocarotenoid pigment, for which the chlorophycean microalga Haematococcus pluvialis is an outstanding natural source. Although information on astaxanthin accumulation in H. pluvialis has substantially advanced in recent years, its underlying molecular bases remain elusive. An integrative metabolic and transcriptomic analysis has been performed for vegetative Haematococcus cells, grown both under N sufficiency (green palmelloid cells) and under moderate N limitation, allowing concurrent active cell growth and astaxanthin synthesis (reddish palmelloid cells). Transcriptional activation was noticeable in reddish cells of key enzymes participating in glycolysis, pentose phosphate cycle and pyruvate metabolism, determining the adequate provision of glyceraldehyde 3 phosphate and pyruvate, precursors of carotenoids and fatty acids. Moreover, for the first time, transcriptional regulators potentially involved in controlling astaxanthin accumulation have been identified, a knowledge enabling optimization of commercial astaxanthin production by Haematococcus through systems metabolic engineering.