Exopolysaccharides from the Energy Microalga Strain Botryococcus braunii: Purification, Characterization, and Antioxidant Activity.

Botryococcus braunii, a prestigious energy microalga, has recently received widespread attention because it can secrete large amounts of exopolysaccharides (EPS) with potential applications in food, cosmetics, and nutraceuticals. Unfortunately, the insufficiency of research on the bioactivity and structure-activity relationship of B. braunii EPS has impeded the downstream applications. In the present study, alcohol precipitation, deproteinization, and DEAE-cellulose column chromatography were used to extract and purify B. braunii SCS-1905 EPS. It was found that B. braunii SCS-1905 EPS were high-molecular-weight heteropolysaccharides containing uronic acid (7.43-8.83%), protein (2.30-4.04%), and sulfate groups (1.52-1.95%). Additionally, the EPS primarily comprised galactose (52.34-54.12%), glucose (34.60-35.53%), arabinose (9.41-10.32%), and minor amounts of fucose (1.80-1.99%), with the presence of a pyranose ring linked by a ß-configurational glycosidic bond. Notably, the antioxidant activity of crude exopolysaccharides (CEPS) was stronger, and the half maximal inhibitory concentration (IC50) for ABTS and hydroxyl radicals was significantly lower than that of deproteinized exopolysaccharides (DEPS). Overall, this study indicated a potential application of B. braunii SCS-1905 EPS as a natural antioxidant. In summary, B. braunii EPS could be used as a potential feedstock for the production of antioxidant health foods.

Effects of glycerol on the fluorescence spectra and chloroplast ultrastructure of Phaeodactylum tricornutum (Bacillariophyta).

Responses of the photosynthetic activity of Phaeodactylum tricornutum (Bacillariophyta) to organic carbon glycerol were investigated. The growth rate, photosynthetic pigments, 77 K fluorescence spectra, and chloroplast ultrastructure of P. tricornutum were examined under photoautotrophic, mixotrophic, and photoheterotrophic conditions. The results showed that the specific growth rate was the fastest under mixotrophic conditions. The cell photosynthetic pigment content and values of Chl a/Chl c were reduced under mixotrophic and photoheterotrophic conditions. The value of carotenoid/Chl a was enhanced under mixotrophic conditions, but was decreased under photoheterotrophic conditions. In comparison with photoautotrophic conditions, the fluorescence emission peaks and fluorescence excitation peaks were not shifted. The relative fluorescence of photosystem (PS) I and PS II and the values of F685/F710 and F685/F738 were decreased. Chloroplast thylakoid pairs were less packed under mixotrophic and photoheterotrophic conditions. There was a strong correlation between degree of chloroplast thylakoid packing and the excitation energy kept in PS II. These results suggested that the PS II activity was reduced by glycerol under mixotrophic conditions, thereby leading to repression of the photosynthetic activity.

[Overcompensation effect of Pavlova viridis under ultraviolet (UV-B) stress].

To examine the existence of overcompensation growth of microalgae, this paper studied the effects of UV-B stress on the production of bioactive substances during the overcompensation of Pavlova viridis. Six groups of UV-B treatments 18, 36, 54, 65, 86 and 108 J x m(-2) as well as the control were set up for this study. After the UV-B stress relieved, the treated groups and the control were simultaneously cultured for 12 days under the same inoculation density and normal culture conditions, and the parameters OD, biomass, chlorophyll a, carotenoid, cellular protein and carbohydrate were measured. The results showed that under UV-B stress, the growth of P. viridis was inhibited significantly (P < 0.05), with a decrease of relative growth rate being 16.15% - 60.00%, compared with the control. But, after the relief of UV-B stress, the growth rate during anaphase was significantly higher (P < 0.05) in UV-B treatments than in the control, indicating the occurrence of overcompensation growth. On the 12th day of culture, the OD, biomass, chlorophyll a, carotenoid, cellular protein and carbohydrate in treated groups were 22.38%, 15.00%, 26.15%, 23.81%, 11.63% and 27.58% higher than those in the control, respectively. The overcompensation growth of P. viridis provided an effective way to exploit the bioactive substances of microalgae.