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

Néstor David Giraldo,Andrés Arbeláez,Sandra Marcela Correa,Felix L Figueroa,Rigoberto Ríos-Estepa,Lucía Atehortúa

doi:10.1186/s40643-021-00389-z

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.

Highlights

The global quest for developing technologies conceived to accelerate the transition from an oil-based and carbon intensive economy into renewable energy infrastructure, Giraldo et al Bioresour
Growth and biomass composition In the present study, we evaluated the response of B. braunii cells cultivated in medium with different M g2+ levels
The results suggested that under the tested concentrations the availability of M g2+ did not cause significant changes in biomass production nor macronutrient consumption during the course of the cultivation period (Fig. 1a–c) similar to the observations previously reported for Chlorella vulgaris (Ben Amor-Ben Ayed et al 2015) and Scenedesmus sp. (Ren et al 2014)

Summary

Introduction

The global quest for developing technologies conceived to accelerate the transition from an oil-based and carbon intensive economy into renewable energy infrastructure, Giraldo et al Bioresour. Besides the changes in the lipid accumulation capacity, a qualitatively TLC analysis showed that the availability of magnesium has a clear influence on the lipid profile of B. braunii cells (Additional file 1: Fig. S2) as the neutral lipid fraction showed an augmented abundance for the lowest M g2+ cultures over the other Mg2+ regimes.

Results

Conclusion