A New Paradigm for Producing Astaxanthin From the Unicellular Green Alga Haematococcus pluvialis

The unicellular green alga Haematococcus pluvialis has been exploited as a cell factory to produce the high-value antioxidant astaxanthin for over two decades, due to its superior ability to synthesize astaxanthin under adverse culture conditions. However, slow vegetative growth under favorable culture conditions and cell deterioration or death under stress conditions (e.g., high light, nitrogen starvation) has limited the astaxanthin production. In this study, a new paradigm that integrated heterotrophic cultivation, acclimation of heterotrophically grown cells to specific light/nutrient regimes, followed by induction of astaxanthin accumulation under photoautotrophic conditions was developed. First, the environmental conditions such as pH, carbon source, nitrogen regime, and light intensity, were optimized to induce astaxanthin accumulation in the dark-grown cells. Althoughmoderate astaxanthin content (e.g., 1% of dry weight) and astaxanthin productivity (2.5mg L-1 day(-1)) were obtained under the optimized conditions, a considerable number of cells died off when subjected to stress for astaxanthin induction. To minimize the susceptibility of dark-grown cells to light stress, the algal cells were acclimated, prior to light induction of astaxanthin biosynthesis, under moderate illumination in the presence of nitrogen. Introduction of this strategy significantly reduced the cell mortality rate under high-light and resulted in increased cellular astaxanthin content and astaxanthin productivity. The productivity of astaxanthin was further improved to 10.5mg L-1 day(-1) by implementation of such a strategy in a bubbling column photobioreactor. Biochemical and physiological analyses suggested that rebuilding of photosynthetic apparatus including D1 protein and PsbO, and recovery of PSII activities, are essential for acclimation of dark-grown cells under photo-induction conditions. (C) 2016 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc

Cellular Capacities for High-Light Acclimation and Changing Lipid Profiles across Life Cycle Stages of the Green Alga Haematococcus pluvialis

The unicellular microalga Haematococcus pluvialis has emerged as a promising biomass feedstock for the ketocarotenoid astaxanthin and neutral lipid triacylglycerol. Motile flagellates, resting palmella cells, and cysts are the major life cycle stages of H. pluvialis. Fast-growing motile cells are usually used to induce astaxanthin and triacylglycerol biosynthesis under stress conditions (high light or nutrient starvation); however, productivity of biomass and bioproducts are compromised due to the susceptibility of motile cells to stress. This study revealed that the Photosystem II (PSII) reaction center D1 protein, the manganese-stabilizing protein PsbO, and several major membrane glycerolipids (particularly for chloroplast membrane lipids monogalactosyldiacylglycerol and phosphatidylglycerol), decreased dramatically in motile cells under high light (HL). In contrast, palmella cells, which are transformed from motile cells after an extended period of time under favorable growth conditions, have developed multiple protective mechanisms-including reduction in chloroplast membrane lipids content, downplay of linear photosynthetic electron transport, and activating nonphotochemical quenching mechanisms-while accumulating triacylglycerol. Consequently, the membrane lipids and PSII proteins (D1 and PsbO) remained relatively stable in palmella cells subjected to HL. Introducing palmella instead of motile cells to stress conditions may greatly increase astaxanthin and lipid production in H. pluvialis culture

Characterization, Stability, and Antibrowning Effects of Oxyresveratrol Cyclodextrin Complexes Combined Use of Hydroxypropyl Methylcellulose

Oxyresveratrol (Oxy) has attracted much attention by employing it as an antibrowning agent in fruits and vegetables. In this study, the formation of cyclodextrin (CD) inclusion exhibited a certain protective effect on Oxy oxidative degradation, while hydroxypropyl-β-cyclodextrin (HP–β-CD) inclusion complex showed stronger stabilizing effects than those of β-cyclodextrin (β-CD). The combined use of CD and hydroxypropyl methylcellulose (HPMC) greatly improved the stability of Oxy–CD inclusion complexes, with approximately 70% of the trans-Oxy retained after 30 days of storage under light conditions at 25 °C. The results of the interaction between CD and Oxy determined by phase solubility studies and fluorescence spectroscopic analysis showed that the binding strength of CD and Oxy increased in the presence of HPMC. Moreover, Oxy combined with ascorbic acid and HPMC showed an excellent antibrowning effect on fresh-cut apple slices during the 48 h test period, indicating that adding HPMC as the third component will not influence the antibrowning activity of Oxy

On-the-fly extrinsic calibration of multimodal sensing system for fast 3D thermographic scanning

The fusion of three-dimensional (3D) geometrical and two-dimensional (2D) thermal information provides a promising method for characterizing temperature distribution of 3D objects, extending infrared imaging from 2D to 3D to support various thermal inspection applications. In this paper, we present an effective on-the-fly calibration approach for accurate alignment of depth and thermal data to facilitate dynamic and fast-speed 3D thermal scanning tasks. For each pair of depth and thermal frames, we estimate their relative pose by minimizing the objective function that measures the temperature consistency between a 2D infrared image and the reference 3D thermographic model. Our proposed frame-to-model mapping scheme can be seamlessly integrated into a generic 3D thermographic reconstruction framework. Through graphics-processing-unit-based acceleration, our method requires less than 10 ms to generate a pair of well-aligned depth and thermal images without hardware synchronization and improves the robustness of the system against significant camera motion

Comparative analyses of lipidomes and transcriptomes reveal a concerted action of multiple defensive systems against photooxidative stress in Haematococcus pluvialis

Haematococcus pluvialis cells predominantly remain in the macrozooid stage under favourable environmental conditions but are rapidly differentiated into haematocysts upon exposure to various environmental stresses. Haematocysts are characterized by massive accumulations of astaxanthin sequestered in cytosolic oil globules. Lipidomic analyses revealed that synthesis of the storage lipid triacylglycerol (TAG) was substantially stimulated under high irradiance. Simultaneously, remodelling of membrane glycerolipids occurred as a result of dramatic reductions in chloroplast membrane glycolipids but remained unchanged or declined slightly in extraplastidic membrane glycerolipids. De novo assembly of transcriptomes revealed the genomic and metabolic features of this unsequenced microalga. Comparative transcriptomic analysis showed that so-called resting cells (haematocysts) may be more active than fast-growing vegetative cells (macrozooids) regarding metabolic pathways and functions. Comparative transcriptomic analyses of astaxanthin biosynthesis suggested that the non-mevalonate pathway mediated the synthesis of isopentenyl diphosphate, as the majority of genes involved in subsequent astaxanthin biosynthesis were substantially up-regulated under high irradiance, with the genes encoding phytoene synthase, phytoene desaturase, and beta-carotene hydroxylase identified as the most prominent regulatory components. Accumulation of TAG under high irradiance was attributed to moderate up-regulation of de novo fatty acid biosynthesis at the gene level as well as to moderate elevation of the TAG assembly pathways. Additionally, inferred from transcriptomic differentiation, an increase in reactive oxygen species (ROS) scavenging activity, a decrease in ROS production, and the relaxation of over-reduction of the photosynthetic electron transport chain will work together to protect against photooxidative stress in H. pluvialis under high irradiance

Effect of high light intensity on pigment contents in <i>H. pluvialis</i>in different cells types.

<p>Pigment contents (mg g⁻¹DW) were measured by HPLC. Values represent means ±SD, n = 6.</p><p>ND: not detected. MC: motile cells; PC: palmella cells; RC-M: red cells induced from motile cells; RC-P: red cells induced from palmella cells.</p><p>Effect of high light intensity on pigment contents in <i>H. pluvialis</i>in different cells types.</p

Content of different glycerolipid classes in different <i>H. pluvialis</i> cells types. Values

<p>represent the mean ± S.D. (n = 6). MC: motile cells; PC: palmella cells; RC-M: red cells induced from motile cells; RC-P: red cells induced from palmella cells. MC: white rectangle; PC: light grey rectangle; RC-M: grey rectangle; RC-P: black rectangle.</p

Analyses of photosystem protein content in different <i>H. pluvialis</i> cells types.

<p>(A) Western blot analyses on protein contents in different cells types; (B) relative protein content in different cells types from these analysis. Values represent the mean ± S.D. (n  =  2). MC: motile cells; PC: palmella cells; RC-M: red cells induced from motile cells; RC-P: red cells induced from palmella cells. MC: white rectangle; PC: light grey rectangle; RC-M: grey rectangle; RC-P: black rectangle.</p

Triacylglycerol (TAG) composition in different <i>H. pluvialis</i> cells types.

<p>(A) Major species; (B) minor species; (C) trace species. Values represent the mean ± S.D. (n = 6). MC: motile cells; PC: palmella cells; RC-M: red cells induced from motile cells; RC-P: red cells induced from palmella cells. MC: white rectangle; PC: light grey rectangle; RC-M: grey rectangle; RC-P: black rectangle.</p

Lipid compositions of four major glycerolipids in <i>H. pluvialis</i> chloroplasts in different cells types.

<p>(A) MGDG; (B) DGDG; (C) SQDG; (D) PG. Values represent the mean ± S.D. (n = 6). MC: motile cells; PC: palmella cells; RC-M: red cells induced from motile cells; RC-P: red cells induced from palmella cells. MC: white rectangle; PC: light grey rectangle; RC-M: grey rectangle; RC-P: black rectangle.</p