Glycine differentially improved the growth and biochemical composition of Synechocystis sp. PAK13 and Chlorella variabilis DT025

Influence of super-optimal light intensity on the acetic acid uptake and microalgal growth in mixotrophic culture of Chlorella sorokiniana in bubble-column photobioreactors

This study seeks to determine the influence of super-optimal light intensity on acetic acid uptake and its associated impact on the cellular composition of Chlorella sorokiniana in a semi-batch mixotrophic cultivation setup. Unicellular green microalga Chlorella sorokiniana is grown in a 1L bubble-column photobioreactor at light intensities from 6000 to 14,000 lx (≈81 to 189 µmol.photons.m-2.s-1). We find that microalgal acetic acid utilization reduces as illumination increases from an optimal 10,000 lx (≈135 µmol.photons.m-2.s-1) to a super-optimal zone (>10000 lx). This lowers microalgal growth (2.75 g/L) and acetic acid intake, which peak at 6 mL/L (10000 lx) and drop to 2 and 1 mL/L at 12,000 and 14,000 lx, respectively. Concurrently, the maximum lipid yield decreases from 0.66 g/L (10000 lx) to 0.54 g/L (12000 lx) and 0.42 g/L (14000 lx). Hence, super-optimal illumination not only disturbs phototrophy but also affects the heterotrophic component, creating an imbalance between the two.

Exploring Exogenous Indole-3-acetic Acid's Effect on the Growth and Biochemical Profiles of Synechocystis sp. PAK13 and Chlorella variabilis

Microalgae have garnered scientific interest for their potential to produce bioactive compounds. However, the large-scale industrial utilization of microalgae faces challenges related to production costs and achieving optimal growth conditions. Thus, this study aimed to investigate the potential role of exogenous indole-3-acetic acid (IAA) application in improving the growth and production of bioactive metabolites in microalgae. To this end, the study employed different concentrations of exogenously administered IAA ranging from 0.36 µM to 5.69 µM to assess its influence on the growth and biochemical composition of Synechocystis and Chlorella. IAA exposure significantly increased IAA levels in both strains. Consequentially, improved biomass accumulation in parallel with increased total pigment content by approximately eleven-fold in both strains was observed. Furthermore, the application of IAA stimulated the accumulation of primary metabolites. Sugar levels were augmented, providing a carbon source that facilitated amino acid and fatty acid biosynthesis. As a result, amino acid levels were enhanced as well, leading to a 1.55-fold increase in total amino acid content in Synechocystis and a 1.42-fold increase in Chlorella. Total fatty acids content increased by 1.92-fold in Synechocystis and by 2.16-fold in Chlorella. Overall, the study demonstrated the effectiveness of exogenously adding IAA as a strategy for enhancing the accumulation of microalgae biomass and biomolecules. These findings contribute to the advancement of microalgae-based technologies, opening new avenues to produce economically important compounds derived from microalgae.