High Light Research Articles

Light-dependent variations in fatty acid profiles and gene expression in Antarctic microalgal cultures.

Photosynthetic eukaryotic microalgae are key primary producers in the Antarctic sea ice environment. Anticipated changes in sea ice thickness and snow load due to climate change may cause substantial shifts in available light to these ice-associated organisms. This study used a laboratory-based experiment to investigate how light levels, simulating different sea ice and snow thicknesses, affect fatty acid (FA) composition in two ice associated microalgae species, the pennate diatom Nitzschia cf. biundulata and the dinoflagellate Polarella glacialis. FA profiling and transcriptomic analyses were used to compare the impact of three light levels: High (baseline culturing conditions 90 ± 1 μmol photons m-2 s-1), mid (10 ± 1 μmol photons m-2 s-1); and low (1.5 ± 1 μmol photons m-2 s-1) on each isolate. Both microalgal isolates had altered growth rates and shifts in FA composition under different light conditions. Nitzschia cf. biundulata exhibited significant changes in specific saturated and monounsaturated FAs, with a notable increase in energy storage-related FAs under conditions emulating thinner ice or reduced snow cover. Polarella glacialis significantly increased production of polyunsaturated FAs (PUFAs) in mid light conditions, particularly octadecapentaenoic acid (C18:5N-3), indicating enhanced membrane fluidity and synthesis of longer-chain PUFAs. Notably, C18:5N-3 has been identified as an ichthyotoxic molecule, with fish mortalities associated with other high producing marine taxa. High light levels caused down regulation of photosynthetic genes in N. cf. biundulata isolates and up-regulation in P. glacialis isolates. This and the FA composition changes show the variability of acclimation strategies for different taxonomic groups, providing insights into the responses of microalgae to light stress. This variability could impact polar food webs under climate change, particularly through changes in macronutrient availability to higher trophic levels due to species specific acclimation responses. Further research on the broader microalgal community is needed to clarify the extent of these effects.

Activation of endogenous tolerance to bleaching stress by high salinity in cloned endosymbiotic dinoflagellates from corals

BackgroundLarge-scale coral bleaching events have become increasingly frequent in recent years. This process occurs when corals are exposed to high temperatures and intense light stress, leading to an overproduction of reactive oxygen species (ROS) by their endosymbiotic dinoflagellates. The ROS buildup prompts corals to expel these symbiotic microalgae, resulting in the corals’ discoloration. Reducing ROS production and enhancing detoxification processes in these microalgae are crucial to prevent the collapse of coral reef ecosystems. However, research into the cell physiology and genetics of coral symbiotic dinoflagellates has been hindered by challenges associated with cloning these microalgae.ResultsA procedure for cloning coral symbiotic dinoflagellates was developed in this study. Several species of coral symbionts were successfully cloned, with two of them further characterized. Experiments with the two species isolated from Turbinaria sp. showed that damage from light intensity at 340 μmol photons/m2/s was more severe than from high temperature at 36 °C. Additionally, preincubation in high salinity conditions activated their endogenous tolerance to bleaching stress. Pretreatment at 50 ppt salinity reduced the percentage of cells stained for ROS by 59% and 64% in the two species under bleaching stress compared to those incubated at 30 ppt. Furthermore, their Fv’/Fm’ during the recovery period showed a significant improvement compared to the controls.ConclusionsThese findings suggest that intense light plays a more important role than high temperatures in coral bleaching by enhancing ROS generation in the symbiotic dinoflagellates. The findings also suggest the genomes of coral symbiotic dinoflagellates have undergone evolutionary processes to develop mechanisms, regulated by gene expression, to mitigate damages caused by high temperature and high light stress. Understanding this gene expression regulation could contribute to strengthening corals’ resilience against the impact of global climate change.

Polyphenolic compounds in Sauvignon Blanc - from grapes to wine

At harvest, the metabolic composition of wine grapes reflects the accumulated effect of the environmental conditions, the stresses endured, and viticultural manipulations applied during the growing season. The role of the winemaker is to extract and nurture this “metabolite potential” throughout the winemaking process. However, it is typically difficult to relate this grape potential to that of the eventual wines. In this study, a holistic view of Sauvignon Blanc grape and wine polyphenolic compounds was attempted by measuring these compounds from different matrices, from ripe grape tissues up to the final wine, including the submatrices, such as juice, pomace and sediment. Sauvignon Blanc vines from one vineyard block were manipulated to yield berries with distinctly different phenolic potentials by creating a high light (HL) or a low light (LL) microclimate in the fruiting zone of the canopy during the growing season. The analyses of the HL and LL berries and wines, as well as concomitant analyses of the phenolic compounds in the submatrices, allowed their tracing as they were (i) transferred from one matrix to another, (ii) lost as waste products, or (iii) affected by different winemaking practices (skin contact and/or fermentation in contact with the juice sediment) implemented in the experimental design. In berries, flavonols showed the largest increase due to sun exposure (HL treatment) but were absent from the juice samples at all juice processing stages. They were however detected in the juice sediment, together with high concentrations of organic acids and sugars. Juice processing was noted for dramatic fluctuations in metabolite concentrations suggesting intense metabolic activity in this pre-fermentation matrix. Both skin contact and sediment contact treatments delivered wines with higher concentrations of coutaric acid (the ester formed from coumaric and tartaric acid) and the flavanol catechin while epicatechin concentrations was unaffected. The higher catechin concentrations did not lead to increased perceived bitterness in the wines, except in the sediment contact treatments. The total phenolic compound concentration of wine from LL (low phenolic potential) grapes was comparable to wine from HL (high phenolic potential) grapes, when skin contact, or sediment contact treatments were employed. From a sensory perspective, the sediment contact decreased the fruity aromas of Sauvignon Blanc, while the skin contact treatment enhanced the sensorial properties of the wines made from the LL grapes, allowing increased extraction from the skin-accumulated impact compounds.

Effects of Light Intensity and Irrigation Method on Growth, Quality, and Anthocyanin Content of Red Oak Lettuce (Lactuca sativa var. cripspa L.) Cultivated in a Plant Factory with Artificial Lighting

Cultivating red oak lettuce in plant factories often encounters challenges in achieving the desired red leaf coloration. To make the leaves a pleasant red color, anthocyanins are key substances that need to be induced. This study aimed to evaluate the effects of increasing light intensity and irrigation methods on the growth and leaf color of red oak lettuce in a controlled environment. Two light intensities (300 and 400 µmol m−2 s−1) with white LEDs and two irrigation methods (circulating vs. non-circulating irrigation) were applied seven days before harvesting. The results indicated that plants grown with circulating irrigation exhibited significantly higher fresh and dry weights than those grown under non-circulating conditions, regardless of light intensity. When non-circulating irrigation was applied, shoot fresh weight decreased by approximately 22% on the harvesting day compared to the circulating treatments. Under the 400 µmol m−2 s−1 light intensity with non-circulating irrigation (400N-C), plants displayed the lowest lightness (L*) at 40.7, increased redness (a*) to −7.4, and reduced yellowness (b*) to 11.0. These changes in coloration were optimized by day 5 after treatment. Additionally, spectral indices, including normalized difference vegetation index and photochemical reflectance index, varied significantly among treatments. The 400N-C treatment also resulted in the highest anthocyanin content and antioxidant activity in red oak lettuce. These findings suggest that combining high light intensity with non-circulating irrigation before harvest can improve both the coloration and quality of red oak lettuce in plant factories with artificial lighting.

Joint Associations of Sedentary Time and Intensity-Specific Physical Activity With Cancer Mortality: A Device-Based Cohort Study of 72,458 UK Adults.

There are no studies examining the prospective joint association of device-based measures of sedentary time and physical activity (PA) with cancer mortality. We examined the joint associations of sedentary time and intensity-specific PA with cancer mortality in 72,458 adults from UK Biobank. Participants wore an Axivity AX3 accelerometer on their dominant wrist for at least 3days (with at least 1 weekend day). Cox regression was performed to estimate hazard ratios (HR) and 95% confidence intervals (CIs) for joint associations of sedentary time and intensity-specific PA (light[LPA], moderate [MPA], and vigorous PA[VPA]) with cancer mortality (reference group: high intensity-specific PA and low sedentary time) adjusted for confounders and mutually adjusted for other PA intensities. Associations between sedentary time and cancer mortality were stronger among participants with low PA, irrespective of the intensity. Compared with participants with lower sedentary time (<11h/d) and high MPA (median of 49min/d), HR were 1.27 (95% CI, 0.90-1.78) for high sedentary time and high MPA, 1.35 (95% CI, 1.03-1.77) for high sedentary time and medium MPA (49min/d), and 1.49 (95% CI, 1.15-1.92) for high sedentary time and low MPA (13min/d). HR for high sedentary time and low light PA (61min/d) and high sedentary time and low vigorous PA (1min/d) were 1.25 (95% CI, 1.02-1.59) and 1.57 (95% CI, 1.20-2.06), respectively. Relatively large amounts of LPA and MPA and small amounts of VPA appeared to attenuate the association between sedentary time and cancer mortality.

Bryophytes as Indicators of Disturbance in One of the Last Remnants of the Mountain Forests of El Oro Province, Ecuador

Epiphytic bryophytes are an important component in terms of the diversity and functioning of montane forests known as biodiversity hotspots. Bryophytes are highly dependent on their external environments because they are sensitive to environmental changes related to disturbance, fragmentation, air pollution, and climate change. The richness and composition of bryophytes in remnants of primary and secondary forests were analyzed, where the richness and cover were recorded on trunk bases of 120 trees. Changes in species richness and diversity were analyzed using generalized linear models (GLMs), and changes in species composition, using multivariate analysis. A total of 57 bryophyte species (36 liverworts and 21 mosses) were recorded in trunk bases. For the first time, 19 new liverworts for the province of El Oro are reported. The richness and diversity of bryophyte species decrease in disturbed forests when compared to primary forests, with a marked decrease in species less adapted to conditions of high light (shade epiphytes). In the same line, species composition is different in each type of forest, where bryophytes with high humidity requirements were abundant in primary forests. This study confirms that forest disturbance is a key factor in determining not only the number of species but also the composition of bryophyte species. The maximum tree diameter and primary forest remnants are important factors in the conservation of sensitive bryophyte species at the base of trees in one of the last remnants of mountain forests in El Oro Province, Ecuador.

Prediction of quaternary SnGeS2As4 monolayer as a promising photocatalyst for water splitting: a DFT study

Abstract The SnGeS2As4 monolayer was studied by first-principles calculations to estimate its potential for used as photocatalyst in water splitting process. The stability of this structure is confirmed based on the analysis of its phonon dispersion and AIDM simulation. The electronic features including density of state (DOS), band structure, and Bader charge were calculated. These data show the role of each constitute element in the formation of covalent π− and σ−bonds, which play important role in stabilizing the buckled honeycomb structure. Besides, the DOS and band structure also provide information regarding to the high light absorption rate α(ω) of 105–105 cm−1. The positions of valence band maximum (VBM) and conduction band minimum (CBM) are suitable for generation of hydrogen and oxygen gases. The SnGeS2As4 monolayer also has optimal work function 5.16 eV for water splitting process and a rather high solar-to-hydrogen efficiency ηSTH = 13.11%. It is worth to note that SnGeS2As4 monolayers with strains ranging from −2% to 6% are still capable to trigger redox reactions in the water splitting process. Moreover, the tensile trains slightly increase the light absorption rates. Such characteristics not only make SnGeS2As4 monolayer a suitable photocatalyst for water splitting but also ensure its performance in wider range of applications

The Detection of Pest Contaminants in Chocolate Using Visible-Near-Infrared Single-Pixel Imaging Technology

Food safety is gaining increasing attention worldwide. Currently, low-density organic foreign objects such as insects are extremely challenging to detect using conventional metal detectors and X-ray inspection systems. This study aimed to develop a visible-near-infrared single-pixel imaging (Vis-NIR-SPI) method to detect small insects inside food. The advantages of Vis-NIR light include its ability to analyze samples non-destructively and measure multiple components simultaneously and quickly, while SPI is robust against dark noise, high scattering, and high equipment costs. The experimental results demonstrated that (1) the newly designed system effectively reduces scattering effects from the highly scattering sample (intralipid 20%), allowing for the capture of information beyond the capabilities of a charge-coupled-device camera; (2) insects positioned behind ham and bread were readily detectable using the imaging reconstruction algorithm; and (3) even for chocolate samples with very high light absorption, only 1 uncontaminated sample out of 100 was mistakenly classified as contaminated, yielding an overall accuracy of 99%. This high level of accuracy underscores the potential of the Vis-NIR-SPI method to provide reliable detection while maintaining sample integrity. Furthermore, this method is cost-effective, offering a practical and efficient solution to improve quality control processes and consumer trust in the food industry.

Green Light Activated Dual-Action Pt(IV) Prodrug With Enhanced PDT activity.

Light induced release of cisplatin from Pt(IV) prodrugs is a promising tool for precise spatiotemporal control over the antiproliferative activity of Pt-based chemotherapeutic drugs. A combination of light-controlled chemotherapy (PACT) and photodynamic therapy (PDT) in one molecule has the potential to overcome crucial drawbacks of both Pt-based chemotherapy and PDT via a synergetic effect. Herein we report green-light-activated Pt(IV) prodrug GreenPt with BODIPY-based photosentitizer in the axial position with an incredible high light response and singlet oxygen generation ability. GreenPt demonstrated the ability to release cisplatin under low-dose green light irradiation up to 1 J/cm2. The investigation of the photoreduction mechanism of GreenPt prodrug using DFT modeling and ΔG0 PET estimation revealed that the anion-radical formation and substituent photoinduced electron transfer from the triplet excited state of the BODIPY axial ligand to the Pt(IV) center is the key step in the light-induced release of cisplatin. Green-light-activated BODIPY-based photosentitizers 5 and 8 demonstrated outstanding photosensitizing properties with an extraordinary phototoxicity index (PI) >1300. GreenPt prodrug demonstrated gradual intracellular accumulation and light-induced phototoxicity with PI > 100, thus demonstrating dual action through light-controlled release of both cisplatin and a potent BODIPY-based photosensitizer.

Nitrogen Assimilation Plays a Role in Balancing the Chloroplastic Glutathione Redox Potential Under High Light Conditions.

Nitrate reduction requires reducing equivalents produced by the photosynthetic electron transport chain. Therefore, it has been suggested that nitrate assimilation provides a sink for electrons under high light conditions. We tested this hypothesis by monitoring photosynthetic efficiency and the chloroplastic glutathione redox potential (chl-EGSH) of plant lines with mutated glutamine synthetase 2 (GS2) and ferredoxin-dependent glutamate synthase 1 (GOGAT1). Mutant lines incorporated significantly less isotopically-labelled nitrate into amino acids than wild-type plants, demonstrating impaired nitrogen assimilation. When nitrate assimilation was compromised, photosystem II (PSII) proved more vulnerable to photodamage. The effect of the nitrate assimilation pathway on the chl- EGSH was monitored using the chloroplast-targeted roGFP2 biosensor (chl-roGFP2). Remarkably, while oxidation followed by reduction of chl-roGFP2 was detected in WT plants in response to high light, oxidation values were stable in the mutant lines, suggesting that chl-EGSH relaxation after high light-induced oxidation is achieved by diverting excess electrons to the nitrogen assimilation pathway. Importantly, similar ΦPSII and chl-roGFP2 patterns were observed at elevated CO2, suggesting that mutant phenotypes are not associated with photorespiration activity. Together, these findings indicate that the nitrogen assimilation pathway serves as a sustainable energy dissipation route, ensuring efficient photosynthetic activity and fine-tuning redox metabolism under light-saturated conditions.

Cobalt tungstate nanoparticles (CoWO4 NPs) affect the photosynthetic performance of the green microalga Raphidocelis subcapitata.

Innovative applications of cobalt tungstate nanoparticles (CoWO4 NPs) are directly linked to their increased production and consumption, which can consequently increase their release into aquatic ecosystems and the exposure of organisms. Microalgae are autotrophic organisms that contribute directly to global primary productivity and provide oxygen for maintaining many organisms on Earth. In this paper, we assessed the toxicity of CoWO4 NPs when in contact with the freshwater microalga Raphidocelis subcapitata (Chlorophyceae). To this end, we assessed algal growth, reactive oxygen species (ROS) production and photosynthetic performance. Our results show that the NPs inhibited the growth of algal cells from 42.37 mg L-1, significantly induced ROS production in the first hours of exposure (1 h) at all concentrations and directly compromised the photosynthetic activity, reinforcing that the oxygen-evolving complex (OEC) is one of the main targets of NPs and that the light curve parameters were the most sensitive endpoints. We observed reductions in the maximum relative electron transport rate (rETRmax) of around 53% and decreases in the saturating irradiance (Ek) of around 40%, which demonstrated that the NPs not only compromised the photosynthetic activity, but also decreased the ability of algal cells to tolerate high light intensities. Our results also highlight that Co was mostly particulate and that the dissolved fraction represented only ∼8% at the lowest concentration and ∼ 0.70% at the highest concentration of CoWO4 NPs, suggesting that the toxicity observed was caused by the NPs. CoWO4 NPs exhibited a high negative surface charge of -33mV in L.C. Oligo medium. The polydispersity index (PdI) varied from 0.22 to 0.45, while the hydrodynamic size ranged from 217.8 ± 11.36 to 503.43 ± 32.78 nm, indicating greater aggregation in this medium. This study elucidates how the CoWO4 NPs interact with R. subcapitata¸ resulting in changes mainly in its photosynthetic performance.

The effects of nickel tungstate nanoparticles (NiWO4 NPs) on freshwater microalga Raphidocelis subcapitata (Chlorophyceae).

Among the vast array of functional nanoparticles (NPs) under development, nickel tungstate (NiWO4) has gained prominence due to its potential applications as a catalyst, sensor, and in the development of supercapacitors. Consequently, new studies on the environmental impact of this material must be conducted to establish a regulatory framework for its management. This work aims to assess the effects of NiWO4 (NPs) on multiple endpoints (e.g., growth, photosynthetic activity, and morphological and biochemical levels) of the freshwater microalga Raphidocelis subcapitata (Chlorophyceae). Quantification data revealed that the fraction of dissolved Ni and free Ni2+ increased proportionally with NiWO4 NP concentrations, although these levels remained relatively low. Biological results indicated that NiWO4 NPs did not inhibit the growth of algal cells, except at 7.9mg L-1, resulting in a 9% decrease. Morphological changes were observed in cell size and complexity, accompanied by physiological alterations, such as a reduction in chlorophyll a fluorescence (FL3-H) and signs of impaired photosynthetic activity, indicated by the effective quantum yield, quenchings, and chlorophyll a (Chl a) content. Furthermore, the rapid light curves showed that the NPs in high concentrations affected microalga ability to tolerate high light intensities, as corroborated by the significant decrease in the relative electron transport rate (rETRmax) and saturation irradiance (Ek). Based on the present study results, we emphasize the importance of applying integrative approaches in ecotoxicological studies, since each endpoint evaluated showed different sensitivity.

The Circadian Response to Evening Light Spectra in Early Childhood: Preliminary Insights.

Although the sensitivity of the circadian system to the characteristics of light (e.g., biological timing, intensity, duration, spectrum) has been well studied in adults, data in early childhood remain limited. Utilizing a crossover, within-subjects design, we examined differences in the circadian response to evening light exposure at two different correlated color temperatures (CCT) in preschool-aged children. Healthy, good sleeping children (n = 10, 3.0-5.9 years) completed two 10-day protocols. In each protocol, after maintaining a stable sleep schedule for 7 days, a 3-day in-home dim-light circadian assessment was performed. On the first and third evenings of the in-home protocol, dim-light melatonin onset (DLMO) was assessed. On the second evening, children received a 1-h light exposure of 20 lux from either 2700 K (low CCT) or 5000 K (high CCT) (~9 and ~16 melanopic equivalent daylight illuminance (mEDI lux), respectively) centered around their habitual bedtime. Children received the remaining light condition during their second protocol, with the order counterbalanced across participants. Salivary melatonin was collected to compute melatonin suppression and circadian phase shift resulting from each experimental light condition. Melatonin suppression across the 1-h light stimulus was significantly greater during exposure to the high CCT light (M = 56.3%, SD = 19.25%) than during the low CCT light (M = 23.90%, SD = 41.06%). Both light conditions resulted in marked delays of circadian timing, but only a small difference (d = -0.25) was observed in the delay between the 5000 K (M = 35.3 min, SD = 34.3 min) and 2700 K (M = 26.7 min, SD = 15.9 min) conditions. Together, these findings add to a growing literature demonstrating high responsivity of the circadian clock to evening light exposure in early childhood and provide preliminary evidence of melatonin suppression sensitivity to differences in light spectrum in preschool-aged children.

Excitation Spillover from PSII to PSI in Leaves at 77K

ABSTRACT Heterogeneous distribution of PSI and PSII in thick grana in shade chloroplasts is argued to hinder spillover of chlorophyll excitations from PSII to PSI. To examine this dogma, we measured fluorescence induction at 77K at 690 nm (PSII) and 760 nm (mostly PSI) in the leaf discs of Spinacia oleracea, Cucumis sativus and shade tolerant Alocasia odora, grown at high and low light, and quantified their spillover capacities. PSI fluorescence (FI) consists of the intrinsic PSI fluorescence (FIα) and fluorescence caused by excitations spilt over from PSII (FIβ). When FI and FII parameters between State 1 and State 2, induced by weak far-red and blue light, were compared, PSII maximum fluorescence (FIIm) and FIβ were greater, and FIα was smaller in State 1 and thereby the spillover ratio, FIβ/(FIα+FIβ), was greater in State 1. When non-photochemical quenching (NPQ) was induced, the spillover ratio decreased. Since analyses of Fv/Fm spectra tentatively suggested that about 15% of Fm at 760 nm was from PSII, all data were corrected accordingly. Even after the correction, the spillover ratio in FIm in State 1 ranged from 16 to 28%. The spillover ratios did not greatly differ between the species or growth light levels. Although extensive grana in low light grown plants would suggest that PSII and PSI are too separated for spillover, the ratios of non-appressed thylakoid membranes/total thylakoid membranes in A. odora chloroplasts were little affected by growth light and more than 40%. Abundant non-appressed thylakoids and margins of appressed-thylakoids would enable efficient spillover. (250 words)

Photoacclimation strategies of Chlamydomonas reinhardtii in response to high-light stress in stationary phase.

Under ideal conditions, Chlamydomonas reinhardtii can photoacclimate to excess light through various short- and long-term mechanisms. However, how microalgae handle excess light stress once they exit exponential growth, and especially in stationary phase, is less understood. Our study explored C. reinhardtii's photoprotection capacity and acclimation strategies during high-light stress once batch culture growth reached stationary phase. We monitored cultures of wildtype strain (CC125) over five days once they reached stationary phase under both low-light (LL) and high-light (HL) conditions. Under HL, many photosynthetic proteins were degraded but the stress-related light harvesting complex protein (LHCSR) was rapidly induced and contributed to the rapid activation of nonphotochemical quenching (NPQ). However, the LHCSR3-defective mutant (CC4614, npq4) lacked the rapid induction of quenching typical of post-exponential cultures, indicating that LHCSR3 is required for this response in stationary phase. Collectively, the main strategy for photoacclimation in stationary phase appears to be a dramatic reduction of photosystems while maintaining LHCII-LHCSR antenna complexes that prime the antenna for rapid activation of quenching upon light exposure. Part of this response to HL involves a resumption of cell growth after two days, that we hypothesized is due to the stimulation of growth-regulating pathways due to increased metabolite pools from the HL-induced protein turnover in the cell, something that remains to be tested. These findings demonstrate how C. reinhardtii manages high-light stress during stationary phases to maximize longevity.

Polybutylene succinate/lignin composites with tunable optical, mechanical, and thermal properties based on fractionation treatment.

The inherent heterogeneity, poor compatibility with polymers, and dark color of lignin limit its application in composites. In this study, original lignin (OL) was fractionated sequentially using four green organic solvents to obtain lignin fractions with different chemical structures. These well-defined lignin fractions were then blended with polybutylene succinate (PBS) to fabricate biocomposites. These composites prepared from fractionated lignin displayed improved properties. In particular, controlled tuning and selective enhancement of the composite properties were achieved by changing the lignin fraction. Benefiting from its rich phenolic acidic structure, the low molecular-weight lignin exhibited near perfect compatibility with PBS. Meanwhile, this composite had both great UV shielding properties and high visible light transmission. At a lignin content of 30 %, the elongation at break of PBS/low molecular-weight lignin remained at 315 %, while the visible light transmission reached 55.5 %. The high syringyl to guaiacyl ratio (S/G) and abundant conjugated structures of high molecular-weight lignin imparted superior rigidity and thermal stability to the composites. These findings highlight the potential of lignin fractionation as a sustainable and green strategy for the controlled preparation of lignin-based composites, offering new opportunities for UV shielding materials with high visible light transmittance.

Enhanced carbon dioxide bio-fixation and protein production of Chlorella pyrenoidosa through a highly efficient sequential heterotrophic and photoautotrophic culture strategy

Chlorella pyrenoidosa is one of the most promising microalgae for protein production with carbon dioxide (CO2) bio-fixation. However, the high production cost and low production capability under traditional photoautotrophic culture mode had severely limited its application. Here, a highly efficient sequential heterotrophic and photoautotrophic cultivation strategy was established. Firstly, the heterotrophic seeds culture conditions were optimized with glucose as the carbon source and 1 g L−1 of yeast extract was selected as a useful stimulus to boost cell growth. Then, the heterotrophic cells were transferred to photoautotrophic conditions directly and cultured under varied concentrations of CO2. Moreover, 8 % (v/v) of CO2, high light and high initial cell density were found to be beneficial for cell growth and CO2 sequestration. Finally, different initial nitrogen concentrations and nitrogen feeding strategies were evaluated to increase the protein content to 62.69 % of dry biomass. These results provide feasible strategies for efficient CO2 sequestration and protein production jointly in C. pyrenoidosa.

Chloroplast arrangement in finger millet under low-temperature conditions.

Finger millet, a C4 plant with mesophyll and bundle sheath cells, has been cultivated at high altitudes in the Himalayas owing to its adaptability to stressful environments. Under environmental stresses such as high light and drought, finger millet mesophyll chloroplasts move toward the bundle sheath, a phenomenon known as aggregative arrangement. To investigate the effect of low temperatures on mesophyll chloroplast arrangement in finger millet, we conducted microscopic observations and photochemical measurements using leaves treated at different temperatures in light or darkness, with or without pharmacological inhibitors. Abscisic acid (ABA) content was also quantified. Chloroplast aggregative arrangement was induced at 5 °C in a light- and actin-dependent manner. This response required a lower intensity of blue light than that previously observed at moderate temperatures. Low temperature significantly reduced the maximum quantum efficiency of photosystem II and increased leaf ABA content in the light. Conversely, in the absence of blue light at low temperatures or under actin-inhibited conditions, mesophyll chloroplasts exhibited a doughnut-like arrangement, characterized by a distribution away from the bundle sheath side. In finger millet, mesophyll chloroplasts move toward the bundle sheath through a blue light and actin-based mechanism at low temperatures. The doughnut-like arrangement appears to be a contingent phenomenon that manifests when the dispersion of mesophyll chloroplasts toward the bundle sheath is impeded. The aggregative arrangement is a response to various environmental stresses, including low temperatures, and may be advantageous for finger millet seedlings in mitigating photoinhibition during cool mornings.

Diurnal rhythm of carotenoid metabolism in the intertidal red algal seaweed Neoporphyra haitanensis

Biological rhythms governing metabolic and developmental processes are widespread in organisms, ranging from prokaryotic cyanobacteria to mammals and flower plants. Species of the genus Porphyra sensu lato (e.g., Porphyra, Pyropia, Neoporphyra, etc.) are major red algal seaweeds important to the marine fisheries industry in northeast Asia. Over a long evolutionary history, these seaweeds have adapted to the intertidal zone environment, which is characterized by periodic extreme stresses such as high light, high temperature, high salinity, and drought. However, very little is known about the rhythmic regulation of these seaweeds in response to the shifting environment. In this study, we entrained N. haitanensis thalli with a 12 h/12 h light/dark regime under constant temperature and light intensity, and analyzed the contents of carotenoid constituents and the transcript abundances of genes involved in carotenoid metabolism. Our results clearly demonstrated a 1.52 (zeaxanthin)–2.13 (β-carotene)-fold change between the highest and lowest amounts of carotenoids, and a 7.66 (NhCHYB)–224.00 (NhZISO)-fold change in the expression levels of genes, over the course of a day. These variations indicate that the fluctuations at both metabolic and transcriptional levels of carotenoid metabolism during the light/dark shifting are significant and cannot be neglected, highlighting the need to use a series of parallel non-treated controls instead of a pre-treatment control to avoid the potential confounding effects of the treatment and the diurnal rhythm.

Xanthosine-mediated modulation of Haematococcus pluvialis growth and stress response under high light: Insights from physiological and transcriptome analysis

Xanthosine-mediated modulation of Haematococcus pluvialis growth and stress response under high light: Insights from physiological and transcriptome analysis