Biochemical and morphological characterization of freshwater microalga Tetradesmus obliquus (Chlorophyta: Chlorophyceae).

Tetradesmus is a microalgal genus with biotechnological potential due to its rapid production of biomass, which is plenty in proteins, carbohydrates, lipids, and bioactives. However, its morphology and physiology need to be determined to guide better research to optimize the species cultivation and biocompounds processing. Thus, this study describes the biochemistry and morphology of the strain Tetradesmus obliquus BR003, isolated from a sample of freshwater reservoirs in a Brazilian municipality. In the T. obliquus BR003 dry biomass, we identified 61.6% unsaturated fatty acids, and 3.4% saturated fatty acids. Regarding other compounds, 28.50 ± 1.47 g soluble proteins/100 g, 0.14 ± 0.009 g carotenoids/100 g, 0.76 ± 0.013 g chlorophyll a/100 g, and 0.42 ± 0.015 g chlorophyll b/100 g with a chlorophyll a/b ratio of 1.8 were detected. The main chemical elements found were S, Mg, and P. The cells of BR003 were elliptically curved at the ends and without appendages. Histochemical tests showed carbohydrates distributed in the cytoplasm and pyrenoids, some lipid droplets, and proteins. The cytoplasm is rich in vacuoles, rough endoplasmic reticulum, mitochondria, and chloroplasts. The nucleus has a predominance of decondensed chromatin, and the cell wall has three layers. Chloroplasts have many starch granules and may be associated with a spherical central pyrenoid. To the best of our knowledge, this was the first biochemical description combined with ultrastructural morphological characterization of the strain T. obliquus BR003, grown under standard conditions, to demonstrate specific characteristics of the species.

Combination of trace elements and salt stress in different cultivation modes improves the lipid productivity of Scenedesmus spp.

The genus Scenedesmus harbors around 120 species, and some strains have been successfully used for mass culture and biotechnological applications. Considering the potential of this genus as a promising feedstock for production of biofuels, mainly biodiesel, it was evaluated the combined effects of trace elements, salinity stress and different cultivation modes (single batch, semi-continuous, and two-stage batch) on lipid productivity of the freshwater strains S. obliquus BR003 and S. bajacalifornicus BR024. Cultivation of BR003 and BR024 applying culture medium supplemented with trace elements and salt stress sustained a higher production of lipids. However, S. obliquus BR003 and S. bajacalifornicus BR024 showed different concentrations of neutral and total lipids when cultivated in batch-based and semi-continuous modes, and the batch-based modes were preferred for the production of lipids and carbohydrates. Consequently, different cultivation strategies coupled with slight salt stress improve the lipid productivity in Scenedesmus strains.