Physiological and Biochemical Responses in Microalgae Dunaliella salina, Cylindrotheca closterium and Phormidium versicolor NCC466 Exposed to High Salinity and Irradiation

Salicylic Acid Improved the Growth of Dunaliella salina and Increased the Proportion of 9-cis-β-Carotene Isomers

Dunaliella salina is an important source of natural β-carotene (containing 9-cis and all trans isomers) for industrial production. The phytohormone salicylic acid (SA) has been proven to have impacts on the stress resistance of higher plants, but research on microalgae is currently unclear. In this study, the effects of SA on the growth, biochemical composition, antioxidant enzyme activity, key enzymes of β-carotene synthesis, and cis-and trans-isomers of β-carotene in D. salina under different salt concentrations were investigated. The results were shown that at concentrations of 1.5, 2, and 2.5 M NaCl, the antioxidant enzyme activity and key enzymes for β-carotene synthesis in algal cells were significantly increased, but the content and proportion of 9-cis isomer in β-carotene isomers decreased. The addition of SA significantly increased the growth and antioxidant enzyme (SOD, MDA) activity, as well as the synthesis of key enzyme phytoene synthase (PSY), phytoene desaturase (PDS), and lycopene β cyclase (LCYB) of D. salina under high-salinity conditions. It is worth noting that under the treatment of SA, the proportion of 9-cis isomer in the three salt concentrations (1.5, 2, 2.5 M NaCl) significantly increased by 32.09%, 20.30%, and 11.32%, respectively. Moreover, SA can not only improve the salt tolerance of D. salina, but also increase the proportion of 9-cis isomer, with higher physiological activity in β-carotene, thereby enhancing the application value of D. salina.

Bioactive Potential of the Sulfated Exopolysaccharides From the Brown Microalga Halamphora sp.: Antioxidant, Antimicrobial, and Antiapoptotic Profiles

This study aims to investigate the physicochemical characteristics of the exopolysaccharides (EPS) extracted from the microalgae species Halamphora sp., as well as to evaluate their antioxidant, antibacterial, and anti-apoptotic activities. The crude extracellular polysaccharides from the halophilic diatom Halamphora sp. were found to be extracellular heterosulfated anionic polysaccharides containing carbohydrates (76.33 ± 1.80%), proteins (0.15 ± 0.02%), uronic acids (5.44 ± 0.08%) and sulfate (7.56 ± 0.86%). The lowest protein (0.24%) and lipid (0.15%) contents suggested that EPS was highly pure. Gas chromatography-mass spectrometry analysis revealed that the carbohydrate fraction consisted of xylose, l-galactose, d-galactose, glucose, ribitol, mannose, and inositol with corresponding mole percentages of 40.55, 13.25, 13.00, 9.95, 9.82, 2.90, and 2.28, respectively. In vitro, tests showed a high total antioxidant capacity probably related to l-galactose followed by d-galactose, uronic acid, and ribitol. In addition, extracellular polysaccharides (EPS) demonstrated effective antimicrobial Gram + properties with inhibition zones ranging from 10 to 12 mm. Molecular docking showed an antiapoptotic effect, as the best docking score was generated due to the interaction of xylose and caspase 3 (-6.9 kcal/mol) and l-galactose and caspase 3 (-5 kcal/mol). Overall, the findings of this study suggest the possibility of using the EPS extract of Halamphora sp. as an additive for nutraceutical and cosmetic purposes.

Photosynthetic response of Chlamydomonas reinhardtii and Chlamydomonas sp. 1710 to zinc toxicity

Zinc (Zn) is an essential trace element but can lead to water contamination and ecological deterioration when present in excessive amounts. Therefore, investigating the photosynthetic response of microalgae to Zn stress is of great significance. In this study, we assessed the photosynthetic responses of neutrophilic Chlamydomonas reinhardtii and acidophilic Chlamydomonas sp. 1710 to Zn exposure for 96 h. The specific growth rate (μ), chlorophyll-a (Chl-a) content, and chlorophyll fluorescence parameters were determined. The results demonstrated that Chlamydomonas sp. 1710 was much more tolerant to Zn than C. reinhardtii, with the half-maximal inhibitory concentration (IC50) values of 225.4 mg/L and 23.4  mg/L, respectively. The μ and Chl-a content of C. reinhardtii decreased in the presence of 15  mg/L Zn, whereas those of Chlamydomonas sp. 1710 were unaffected by as high as 100  mg/L Zn. Chlorophyll fluorescence parameters indicated that the regulation of energy dissipation, including non-photochemical quenching, played a crucial role in Zn stress resistance for both Chlamydomonas strains. However, in the case of C. reinhardtii, non-photochemical quenching was inhibited by 5  mg/L Zn in the first 48 h, whereas for Chlamydomonas sp. 1710, it remained unaffected under 100  mg/L Zn. Chlamydomonas sp. 1710 also exhibited a 20 times stronger capacity for regulating the electron transfer rate than C. reinhardtii under Zn stress. The light energy utilization efficiency (α) of Chlamydomonas sp. 1710 had the most highly non-linear correlation with μ, indicating the energy utilization and regulation process of Chlamydomonas sp. 1710 was well protected under Zn stress. Collectively, our findings demonstrate that the photosystem of Chlamydomonas sp. 1710 is much more resilient and tolerant than that of C. reinhardtii under Zn stress.

Modification in the ascorbate-glutathione cycle leads to a better acclimation to high light in the rose Bengal resistant mutant of Nannochloropsis oceanica

Understanding how to adapt outdoor cultures of Nannochloropsis oceanica to high light (HL) is vital for boosting productivity. The N. oceanica RB2 mutant, obtained via ethyl methanesulfonate mutagenesis, was chosen for its tolerance to Rose Bengal (RB), a singlet oxygen (1O2) generator. Compared to the wild type (WT), the RB2 mutant showed higher resilience to excess light conditions. Analyzing the ascorbate-glutathione cycle (AGC), involving ascorbate peroxidases (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.8.1.7), in the RB2 mutant under HL stress provided valuable insights. At 250 μmol photon m-2 s-1 (HL), the WT strain displayed superoxide anion radicals (O2▪-) and hydrogen peroxide (H2O2) accumulation, increased lipid peroxidation, and cell death compared to normal light (NL) conditions (50 μmol photon m-2 s-1). The RB2 mutant didn't accumulate O2▪- and H2O2 after HL exposure, and exhibited increased APX, DHAR, and GR activities and transcript levels compared to WT and remained consistent after HL treatment. Although the RB2 mutant had a smaller ascorbate (AsA) pool than the WT, its ability to regenerate dehydroascorbate (DHA) increased post HL exposure, indicated by a higher AsA/DHA ratio. Additionally, under HL conditions, the RB2 mutant displayed an improved glutathione (GSH) regeneration rate (GSH/GSSG ratio) without changing the GSH pool size. Remarkably, H2O2 or menadione (a O2▪- donor) treatment induced cell death in the WT strain but not in the RB2 mutant. These findings emphasize the essential role of AGC in the RB2 mutant of Nannochloropsis in handling photo-oxidative stress.

Hyperhalophilic Diatom Extract Protects against Lead-Induced Oxidative Stress in Rats and Human HepG2 and HEK293 Cells

This work investigated the protective effects of microalga Halamphora sp. extract (HExt), a nutraceutical and pharmacological natural product, on human lead-intoxicated liver and kidney cells in vitro and in vivo in Wistar rats. The human hepatocellular carcinoma cell line HepG2 and the human embryonic kidney cell line HEK293 were used for the in vitro study. The analysis of the fatty acid methyl esters in the extract was performed via GC/MS. The cells were pretreated with HExt at 100 µg mL-1, followed by treatment with different concentrations of lead acetate, ranging from 25 to 200 µM for 24 h. The cultures were incubated (5% CO, 37 °C) for 24 h. Four groups, each containing six rats, were used for the in vivo experiment. The rats were exposed to subchronic treatment with a low dose of lead acetate (5 mg kg-1 b.w. per day). Pretreating HepG2 and HEK293 cells with the extract (100 µg mL-1) significantly (p < 0.05) protected against the cytotoxicity induced by lead exposure. For the in vivo experiment, the biochemical parameters in serum-namely, the level of malondialdehyde (MDA), and the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx)-were measured in the organ homogenate supernatants. HExt was found to be rich in fatty acids, mainly palmitic and palmitoleic acids (29.464% and 42.066%, respectively). In both the in vitro and in vivo experiments, cotreatment with HExt protected the liver and kidney cell structures and significantly preserved the normal antioxidant and biochemical parameters in rats. This study discovered the possible protective effect of HExt, which could be beneficial for Pb-intoxicated cells.

Solar Salterns and Pollution: Valorization of Some Endemic Species as Sentinels in Ecotoxicology

Solar salterns and salt marshes are unique ecosystems with special physicochemical features and characteristic biota. Currently, there are very few studies focused on the impacts of pollution on these economic and ecological systems. Unfortunately, diversified pollution (metals, Polycyclic Aromatic Hydrocarbons, etc.) has been detected in these complex ecosystems. These hypersaline environments are under increasing threat due to anthropogenic pressures. Despite this, they represent a valuable source of microbial diversity, with taxa displaying special features in terms of environmental remediation capacities as well as economical species such as Artemia spp. (Branchiopoda) and Dunaliella salina (Chlorophyta). In this review, we discuss the impacts of pollution on these semi-artificial systems. Therefore, we have indicated the sentinel species identified in plankton communities, which can be used in ecotoxicological investigations in solar salterns. In future, researchers should increase their interest in pollution assessment in solar salterns and salt marshes.