Background: Haematococcus pluvialis, a green microalga, is a rich source of natural astaxanthin and a potent antioxidant with high commercial value. This study investigates the biological characteristics and potential of H. pluvialis HB isolated from Hoa Binh, Vietnam, for growth and astaxanthin accumulation using a two-phase culture method. Methods: H. pluvialis HB was cultured in a C/RM medium at 25 °C, and morphological characteristics were examined. NMR spectroscopy was used to determine the structure of the astaxanthin, which was extracted using the Soxhlet method. Results: After 22 days, the highest cell density (4.96 × 10⁶ cells mL⁻¹) was achieved under optimized light and ultraviolet conditions. Nutrient deprivation followed by bicarbonate supplementation resulted in a maximal astaxanthin accumulation of 48.8 mg g⁻¹ dry cell weight within two days. The extracted astaxanthin demonstrated potent antioxidant activity (IC₅₀: 3.74 mg mL⁻¹) compared to ascorbic acid (IC₅₀: 18.53 µg mL⁻¹) and exhibited strong acetylcholinesterase inhibition (IC₅₀: 297.99 µg mL⁻¹). It also showed neuroprotective effects against H₂O₂ and amyloid beta-induced neurotoxicity in C6 cells. Conclusions: This study highlights H. pluvialis HB as a promising source for large-scale astaxanthin production with potential applications in neuroprotective health products.

Aurantiochytrium is a heterotrophic marine microalga that has potential industrial applications. The main objectives of this study were to isolate an Aurantiochytrium strain from Sand Cay (Son Ca) Island, Vietnam, optimize its culture conditions, determine its nutritional composition, extract polyunsaturated fatty acids (PUFAs) in the free (FFA) and the alkyl ester (FAAE) forms, and evaluate the antioxidation and neuroprotection properties of the PUFAs. Aurantiochytrium sp. SC145 can be grown stably under laboratory conditions. Its culture conditions were optimized for a dry cell weight (DCW) of 31.18 g/L, with total lipids comprising 25.29%, proteins 7.93%, carbohydrates 15.21%, and carotenoid at 143.67 µg/L of DCW. The FAAEs and FFAs extracted from Aurantiochytrium sp. SC145 were rich in omega 3–6–9 fatty acids (40.73% and 44.00% of total fatty acids, respectively). No acute or subchronic oral toxicity was determined in mice fed with the PUFAs in FFA or FAAE forms at different doses over 90 days. Furthermore, the PUFAs in the FFA or FAAE forms and their main constituents of EPA, DHA, and ALA showed antioxidant and AChE inhibitory properties and neuroprotective activities against damage caused by H₂O₂- and amyloid-ß protein fragment 25–35 (Aβ_25-35)-induced C6 cells. These data suggest that PUFAs extracted from Aurantiochytrium sp. SC145 may be a potential therapeutic target for the treatment of neurodegenerative disorders.

This paper studied the diversity of phytoplankton species at 9 sampling points of aquaculture ponds in Dak Ha, Sa Thay and Kon Plong districts, Kon Tum province (now Quang Ngai province) in 2022–2023. The results recorded 7 phyla, 98 genera, and 142 species, of which 22 genera and 23 species of phytoplankton were present in all 3 sampling periods. The values of the biodiversity index (H’) and the diversity value index (Dv) at 9 sampling points ranged from 2.51–3.66 and 2.39–3.58, indicating that the diversity of phytoplankton in aquaculture ponds is high and very high, respectively. The regulation index (J) ranged from 0.95 to 0.99, indicating that phytoplankton species were evenly distributed at all studied sampling points. The similarity coefficient of species composition of phytoplankton populations at 9 sampling points ranged from 0.43 - 0.85. In water samples collected at 9 study locations, the number of phytoplankton species was negatively correlated with impedance. In particular, at the sampling locations, the main environmental factors such as suspended solids, salinity, and conductivity affecting the cell density of phytoplankton communities had a positive correlation and a negative correlation with impedance.