Reducing self-shading effects in Botryococcus braunii cultures: effect of Mg2+ deficiency on optical and biochemical properties, photosynthesis and lipidomic profile

Abstract

Microalgae biomass exploitation as a carbon–neutral energy source is currently limited by several factors, productivity being one of the most relevant. Due to the high absorption properties of light-harvesting antenna, photosynthetic cells tend to capture an excessive amount of energy that cannot be entirely channeled through the electron transfer chain that ends up dissipated as heat and fluorescence, reducing the overall light use efficiency. Aiming to minimize this hurdle, in this work we studied the effect of decreasing concentrations of Magnesium (Mg2+) on the chlorophyll a content, photosynthetic performance, biomass and lipid production of autotrophic cultures of Botryococcus braunii LB 572. We also performed, for the first time, a comparative lipidomic analysis to identify the influence of limited Mg2+ supply on the lipid profile of this algae. The results indicated that a level of 0.0037 g L−1 MgSO4 caused a significant decline on chlorophyll a content with a concomitant 2.3-fold reduction in the biomass absorption coefficient. In addition, the Mg2+ limitation caused a decrease in the total carbohydrate content and triggered lipid accumulation, achieving levels of up to 53% DCW, whereas the biomass productivity remained similar for all tested conditions. The lipidome analysis revealed that the lowest Mg2+ concentrations also caused a differential lipid profile distribution, with an enrichment of neutral lipids and an increase of structural lipids. In that sense, we showed that Mg2+ limitation represents an alternative optimization approach that not only enhances accumulation of neutral lipids in B. braunii cells but also may potentially lead to a better areal biomass productivity due to the reduction in the cellular light absorption properties of the cells.

Fine-tuned regulation of photosynthetic performance via γ-aminobutyric acid (GABA) supply coupled with high initial cell density culture for economic starch production in microalgae

“…One of the strategies raised to deal with this problem is to adopt a two-stage mode, where in the first stage, the algae cells are cultivated in an optimal condition to achieve high biomass accumulation and then transferred into a stressful condition under a specific physiological status for starch production as the second stage. The initial cell density (ICD) for the second stage is a key factor that affects biomass and starch productivity especially under the photoautotrophic cultivation mode (Carnovale et al 2021 ; Cheng et al 2017 ; Ivanov et al 2021 ; Yao et al 2013a ; Giraldo et al 2021 ). High cell density influences the accessibility of light penetration through the culture medium due to the mutual shading, thus altering the mean light intensity that individual algal cell would receive (Brányiková et al 2011 ; Carnovale et al 2021 ; Yao et al 2013a ).…”

Co‐production of bioethanol and commercially important exopolysaccharides from the marine cyanobacterium Synechococcus elongatus BDU 10144 in a novel low‐cost seawater‐fertilizer‐based medium

“…Mg is also a cofactor for about 300 enzymes, a stabilizer of nucleic acid conformation and ribosome structure. Mg also helps to maintain cellular structural integrity 53 . A high cytoplasmic Mg content may limit the K + potential in the inner chloroplast membrane, preventing the elimination of H + ions from the chloroplast stroma, resulting in oxidative damage in the cell 37,54 .…”

“…Mg also helps to maintain cellular structural integrity. 53 A high cytoplasmic Mg content may limit the K + potential in the inner chloroplast membrane, preventing the elimination of H + ions from the chloroplast stroma, resulting in oxidative damage in the cell. 37,54 According to Hanifzadeh et al, 55 excessive quantities of Mg 2+ in the medium increase the chlorophyll content of cells, which may impede light transmission into the culture and limit culture productivity.…”

“…37,54 According to Hanifzadeh et al, 55 excessive quantities of Mg 2+ in the medium increase the chlorophyll content of cells, which may impede light transmission into the culture and limit culture productivity. 53 Potassium is a cofactor for numerous enzymes necessary for growth and is involved in osmotic regulation and protein synthesis. Sulfur is a significant component of certain essential amino acids, vitamins and sulfolipids, which is why sulfur is required for the development of cyanobacteria.…”