Comparative Response of Marine Microalgae to H2O2-Induced Oxidative Stress

Global omics study of Tetraselmis chuii reveals time-related metabolic adaptations upon oxidative stress

Microalgae species encounter oxidative stress in their natural environments, prompting the development of species-specific adaptation mechanisms. Understanding these mechanisms can offer valuable insights for biotechnological applications in microalgal metabolic manipulation. In this study, we investigated the response of Tetraselmis chuii, an industrially important microalga, to H2O2-induced oxidative stress. Exposure to 0.5-mM H2O2 resulted in reduced cell viability, and higher concentrations led to a drastic decline. After 1 h of exposure to H2O2, photosynthetic capacity (Qy) was negatively impacted, and this reduction intensified after 6 h of continuous stress. Global multi-omics analysis revealed that T. chuii rapidly responded to H2O2-induced oxidative stress within the first hour, causing significant changes in both transcriptomic and metabolomic profiles. Among the cellular functions negatively affected were carbon and energy flow, with photosynthesis-related PSBQ having a 2.4-fold downregulation, pyruvate kinase decreased by 1.5-fold, and urea content reduced by threefold. Prolonged exposure to H2O2 incurred a high energy cost, leading to unsuccessful attempts to enhance carbon metabolism, as depicted, for example, by the upregulation of photosystems-related PETC and PETJ by more than twofold. These findings indicate that T. chuii quickly responds to oxidative stress, but extended exposure can have detrimental effects on its cellular functions. KEY POINTS: • 0.5-mM H2O2-induced oxidative stress strongly affects T. chuii • Distinct short- and long-term adaptation mechanisms are induced • Major metabolic adaptations occur within the first hour of exposure.

Bioactivity of Amphidinol-Containing Extracts of Amphidinium carterae Grown Under Varying Cultivation Conditions

Microalgae are of great interest due to their ability to produce valuable compounds, such as pigments, omega-3 fatty acids, antioxidants, and antimicrobials. The dinoflagellate genus Amphidinium is particularly notable for its amphidinol-like compounds, which exhibit antibacterial and antifungal properties. This study utilized a two-stage cultivation method to grow Amphidinium carterae CCAP 1102/8 under varying conditions, such as blue LED light, increased salinity, and the addition of sodium carbonate or hydrogen peroxide. After cultivation, the biomass was extracted and fractionated using solid-phase extraction, yielding six fractions per treatment. These fractions were analyzed using Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS/MS) to identify their chemical components. Key amphidinol compounds (AM-B, AM-C, AM-22, and AM-A) were identified, with AM-B being the most abundant in Fraction 4, followed by AM-C. Fraction 5 also contained a significant amount of AM-C along with an unknown compound. Fraction 4 returned the highest antimicrobial activity against the pathogens Staphylococcus aureus, Enterococcus faecalis, and Candida albicans, with Minimal Biocidal Concentrations (MBCs) ranging from 1 to 512 µg/mL. Results indicate that the modulation of both amphidinol profile and fraction bioactivity can be induced by adjusting the cultivation parameters used to grow two-stage batch cultures of A. carterae.

Biochemical profiling and antioxidant activity analysis of commercially relevant seaweeds from northwest Europe

BACKGROUND

The drive towards ensuring the sustainability of bioresources has been linked with better valorising primary materials and developing biorefinery pipelines. Seaweeds constitute valuable coastal resources with applications in the bioenergy, biofertiliser, nutrition, pharmaceutical and cosmetic sectors. Owing to the various sought-after metabolites they possess, several seaweed species are commercially exploited throughout Western Europe, including Ireland. Here, four commercially relevant brown (Fucus serratus and Fucus vesiculosus) and red (Chondrus crispus and Mastocarpus stellatus) seaweed species were sampled during a spring tide in July 2021 on moderately exposed shores across three coastal regions in the west of Ireland.

RESULTS

Significant regional differences were identified when specimens were analysed for carbohydrates (max. 80.3 μg glucose eq mg-1 DW), proteins (max. 431.3 μg BSA eq. mg-1 DW), lipids (max. 158.6 mg g-1 DW), pigment signature and antioxidant potential. Protein content for F. serratus recorded a twofold difference between northern and southern specimens. The antioxidant potential of F. vesiculosus and M. stellatus returned greater activity compared to F. serratus and C. crispus, respectively. Multivariate analysis showed a clear latitudinal pattern across the three western coastal regions (north, west and south) for both F. vesiculosus and F. serratus.

CONCLUSION

F. vesiculosus thalli from the northwest were richer in pigment content while the F. serratus thalli from the northwest were richer in antioxidants. Such biogeographic patterns in the biochemical make-up of seaweeds need consideration for the development of regional integrated aquaculture systems and the optimisation of the biomass content for targeted downstream applications. © 2024 Society of Chemical Industry.

The gene AccCyclin H mitigates oxidative stress by influencing trehalose metabolism in Apis cerana cerana

BACKGROUND

Environmental stress can induce oxidative stress in Apis cerana cerana, leading to cellular oxidative damage, reduced vitality, and even death. Currently, owing to an incomplete understanding of the molecular mechanisms by which A. cerana cerana resists oxidative damage, there is no available method to mitigate the risk of this type of damage. Cyclin plays an important role in cell stress resistance. The aim of this study was to explore the in vivo protection of cyclin H against oxidative damage induced by abiotic stress in A. cerana cerana and clarify the mechanism of action. We isolated and identified the AccCyclin H gene in A. cerana cerana and analysed its responses to different exogenous stresses.

RESULTS

The results showed that different oxidative stressors can induce or inhibit the expression of AccCyclin H. After RNA-interference-mediated AccCyclin H silencing, the activity of antioxidant-related genes and related enzymes was inhibited, and trehalose metabolism was reduced. AccCyclin H gene silencing reduced A. cerana cerana high-temperature tolerance. Exogenous trehalose supplementation enhanced the total antioxidant capacity of A. cerana cerana, reduced the accumulation of oxidants, and improved the viability of A. cerana cerana under high-temperature stress.

CONCLUSION

Our findings suggest that trehalose can alleviate adverse stress and that AccCyclin H may participate in oxidative stress reactions by regulating trehalose metabolism. © 2023 Society of Chemical Industry.

Effects of citrate-stabilized gold and silver nanoparticles on some safety parameters of Porphyridium cruentum biomass

Introduction: Our research raises the question of how realistic and safe it is to use gold and silver nanoparticles in biotechnologies to grow microalgae, which will later be used to obtain valuable products. To this purpose, it was necessary to assess the influence of 10 and 20 nm Au and Ag nanoparticles stabilized in citrate on the growth of microalga Porphyridium cruentum in a closed cultivation system, as well as some safety parameters of biomass quality obtained under experimental conditions. Methods: Two types of experiments were conducted with the addition of nanoparticles on the first day and the fifth day of the cultivation cycle. Changes in productivity, lipid content, malondialdehyde (MDA), as well as antioxidant activity of microalgae biomass have been monitored in dynamics during the life cycle in a closed culture system. Results: The impact of nanoparticles on the growth curve of microalgae culture was marked by delaying the onset of the exponential growth phase. A significant increase in the content of lipids and MDA in biomass was noted. Excessive accumulation of lipid oxidation products within the first 24 h of cultivation resulted in altered antioxidant activity of red algae extracts. Discussion: Citrate-stabilized gold and silver nanoparticles proved to be a stress factor for red microalga Porphyridium cruentum, causing significant changes in both biotechnological and biomass safety parameters. Addition of Au and Ag nanoparticles during the exponential growth phase of porphyridium culture led to an enhanced lipid accumulation and reduced MDA values in biomass.

Modulation of the metabolite content of the unicellular rhodophyte Porphyridium purpureum using a 2-stage cultivation approach and chemical stressors

There have been growing interests in microalgal biotechnology for the biorefining of bioactive compounds such as carotenoid pigments, ω-3 fatty acids, antioxidants or antimicrobials for sectoral applications in the pharmacology, nutraceutical and cosmetic fields. This study focused on the unicellular marine rhodophyte Porphyridium purpureum CCAP 1380/1 A, which was cultivated via a two-stage batch growth mode for 10 days using hydrogen peroxide (H₂O₂), the phytohormone methyl jasmonate (MJ) and three plant extracts (Passiflora incarnata, Panax ginseng and Valeriana officinalis). The microalgal biomass was then analysed for its protein, phycoerythtin, carbohydrate and pigment composition together with its pigment content and antioxidant activity. Of note, MJ increased the protein and phycoerythtin content (up to 225 µg BSA eq./mg DW and 15 mg/ml, respectively) while both the MJ and H₂O₂ treatments increased carotenoid pigment yields (β-carotene and zeaxanthin, up to 5 and 4 mg/g, respectively). Carbohydrates were enhanced ∼10 fold by the Valeriana officinalis treatment (up 192 μg starch eq./mg). Overall, neutral lipids and antioxidants were mostly negatively affected by the plant extracts. The greatest antioxidant activity registered was obtained with the H₂O₂ treatment (15 μmol Trolox eq./g DW with TEAC assay). P. purpureum contains multiple valuable compounds of commercial interest. These results indicate that they can be favorably modulated using specific cultivation regimes and chemical enhancers, thereby facilitating the exploitation of the biomass by applying a suitable co-refinery pipeline.

Cold stress combined with salt or abscisic acid supplementation enhances lipogenesis and carotenogenesis in Phaeodactylum tricornutum (Bacillariophyceae)

Compounds from microalgae such as ω3-fatty acids or carotenoid are commercially exploited within the pharmacology, nutraceutical, or cosmetic sectors. The co-stimulation of several compounds of interest may improve the cost-effectiveness of microalgal biorefinery pipelines. This study focussed on Phaeodactylum tricornutum to investigate the effects on lipogenesis and carotenogenesis of combined stressors, here cold temperature and addition of NaCl salt or the phytohormone abscisic acid, using a two-stage cultivation strategy. Cold stress with NaCl or phytohormone addition increased the neutral lipid content of the biomass (20 to 35%). These treatments also enhanced the proportions of EPA (22% greater than control) in the fatty acid profile. Also, these treatments had a stimulatory effect on carotenogenesis, especially the combination of cold stress with NaCl addition, which returned the highest production of fucoxanthin (33% increase). The gene expression of diacylglycerol acyltransferase (DGAT) and the ω-3 desaturase precursor (PTD15) were enhanced 4- and 16-fold relative to the control, respectively. In addition, zeaxanthin epoxidase 3 (ZEP3), was downregulated at low temperature when combined with abscisic acid. These results highlight the benefits of applying a combination of low temperature and salinity stress, to simultaneously enhance the yields of the valuable metabolites EPA and fucoxanthin in Phaeodactylum tricornutum.

Humic Substances as Microalgal Biostimulants—Implications for Microalgal Biotechnology

Humic substances (HS) act as biostimulants for terrestrial photosynthetic organisms. Their effects on plants are related to specific HS features: pH and redox buffering activities, (pseudo)emulsifying and surfactant characteristics, capacity to bind metallic ions and to encapsulate labile hydrophobic molecules, ability to adsorb to the wall structures of cells. The specific properties of HS result from the complexity of their supramolecular structure. This structure is more dynamic in aqueous solutions/suspensions than in soil, which enhances the specific characteristics of HS. Therefore, HS effects on microalgae are more pronounced than on terrestrial plants. The reported HS effects on microalgae include increased ionic nutrient availability, improved protection against abiotic stress, including against various chemical pollutants and ionic species of potentially toxic elements, higher accumulation of value-added ingredients, and enhanced bio-flocculation. These HS effects are similar to those on terrestrial plants and could be considered microalgal biostimulant effects. Such biostimulant effects are underutilized in current microalgal biotechnology. This review presents knowledge related to interactions between microalgae and humic substances and analyzes the potential of HS to enhance the productivity and profitability of microalgal biotechnology.

Antioxidant Activity and Carotenoid Content Responses of Three Haematococcus sp. (Chlorophyta) Strains Exposed to Multiple Stressors

There has been increasing demands worldwide for bioactive compounds of natural origins, especially for the nutraceutical and food-supplement sectors. In this context, microalgae are viewed as sustainable sources of molecules with an array of health benefits. For instance, astaxanthin is a xanthophyll pigment with powerful antioxidant capacity produced by microalgae such as the chlorophyte Haematococcus sp., which is regarded as the most suitable organism for the mass production of this pigment. In this study, three Haematococcus sp. strains were cultivated using a batch mode under favourable conditions to promote vegetative growth. Their environment was altered in a second phase using a higher and constant illumination regime combined with either exposure to blue LED light, an osmotic shock (with NaCl addition) or supplementation with a phytohormone (gibberellic acid, GA3), a plant extract (ginger), an herbicide (molinate) or an oxidant reagent (hydrogen peroxide). The effects of these stressors were evaluated in terms of antioxidant response and astaxanthin and β-carotene accumulation. Overall, strain CCAP 34/7 returned the highest Trolox Equivalent Antioxidant Capacity (TEAC) response (14.1-49.1 µmoL Trolox eq. g^- 1 of DW), while the highest antioxidant response with the Folin-Ciocalteu (FC) was obtained for strain RPFW01 (62.5-155 µmoL Trolox eq. g^- 1 of DW). The highest β-β-carotene content was found in strain LAFW15 when supplemented with the ginger extract (4.8 mg. g^- 1). Strain RPFW01 exposed to blue light returned the highest astaxanthin yield (2.8 mg. g^- 1), 5-fold that of strain CCAP 34/7 on average. This study documents the importance of screening several strains when prospecting for species with potential to produce high-value metabolites. It highlights that strain-specific responses can ensue from exposure of cells to a variety of stressors, which is important for the adequate tailoring of a biorefinery pipeline.

On the Efficacy of H2O2 or S2O82- at Promoting the Inactivation of a Consortium of Cyanobacteria and Bacteria in Algae-Laden Water

Harmful algal blooms in coastal areas can significantly impact a water source. Microorganisms such as cyanobacteria and associated pathogenic bacteria may endanger an ecosystem and human health by causing significant eco-hazards. This study assesses the efficacy of two different reagents, H2O2 and S2O82−, as (pre-)treatment options for algae-laden waters. Anabaena sp. and Vibrio alginolyticus have been selected as target microorganisms. With the objective of activating H2O2 or S2O82−, additional experiments have been performed with the presence of small amounts of iron (18 µmol/L). For the cyanobacterial case, H2O2-based processes demonstrate greater efficiency over that of S2O82−, as Anabaena sp. is particularly affected by H2O2, for which >90% of growth inhibition has been achieved with 0.088 mmol/L of H2O2 (at 72 h of exposure). The response of Anabaena sp. as a co-culture with V. alginolyticus implies the use of major H2O2 amounts for its inactivation (0.29 mmol/L of H2O2), while the effects of H2O2/Fe(II) suggests an improvement of ~60% compared to single H2O2. These H2O2 doses are not sufficient for preventing the regrowth of V. alginolyticus after 24 h. The effects of S2O82− (+ Fe(II)) are moderate, reaching maximum inhibition growth of ~50% for Anabaena sp. at seven days of exposure. Nevertheless, doses of 3 mmol/L of S2O82− can prevent the regrowth of V. alginolyticus. These findings have implications for the mitigation of HABs but also for the associated bacteria that threaten many coastal ecosystems.