Effect of Glycerol Concentration and Light Intensity on Growth and Biochemical Composition of Arthrospira (Spirulina) Platensis: A Study in Semi-Continuous Mode with Non-Aseptic Conditions

Giorgos Markou,Eleni Kougia,Vasiliki Tsagou,Dimitrios Arapoglou,Io Kefalogianni,Iordanis Chatzipavlidis

doi:10.3390/app9214703

Giorgos Markou, Eleni Kougia + Show 4 more

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https://doi.org/10.3390/app9214703

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Abstract

In this study, Arthrospira platensis was grown in the presence of different glycerol concentrations (0.5–9 g/L) under three light intensities (5, 10 and 15 Klux) in semi-continuous mode and under non-axenic conditions. The aim of this study was to investigate the growth performance, the biomass biochemical composition and any interactions between A. platensis and bacteria that would potentially grow as well on glycerol. The results here show that glycerol did not have any positive effect on biomass production of A. platensis. In contrast, it was observed that by increasing glycerol concentration the growth performance of A. platensis was restricted, while a gradual increase of bacteria population was observed, which apparently outcompeted and repressed A. platensis growth. Chlorophyll fluorescence measurements (Quantum Yields) revealed that glycerol was not an inhibiting factor per se of photosynthesis. On the other hand, cyanobacterial biomass grown on glycerol displayed a higher content in proteins and lipids. Especially, protein productivity was enhanced around 15–35% with the addition of glycerol compared to the control. In distinction, carbohydrate and photosynthetic pigments (phycocyanin and chlorophyll-α) content decreased with the increase of glycerol concentration. The results here suggest that A. platensis did not utilize glycerol for biomass production but most probably as metabolic energy carrier towards synthesis of proteins and lipids, which are more energy consuming metabolites compared to carbohydrates. The study revealed that the addition of glycerol at amounts of 0.5–1.5 g/L could be a strategy to improve protein productivity by A. platensis.

Highlights

Arthrospira platensis is a photosynthetic cyanobacterium of high nutritional value due to its high content in proteins, polyunsaturated fatty acids, vitamins etc
The results shown are the averages of three subsequent days of cultivation and reflect the semi-steady state biomass concentration of A. platensis
There was a decrease on biomass concentration with the increase of glycerol concentration, except of the series of the 1st phase with ammonia

Summary

Introduction

Arthrospira platensis (commonly known as Spirulina) is a photosynthetic cyanobacterium of high nutritional value due to its high content in proteins (up to 70%), polyunsaturated fatty acids, vitamins etc. A. platensis along with Chlorella vulgaris are the most widely commercially produced microalgal/cyanobacterial species worldwide and are sold mainly as food supplements. A. platensis is exclusively produced under phototrophic mode in open ponds either indoors or outdoors. Autotrophic mode displays a major drawback related to light limitations due. Sci. 2019, 9, 4703 to the poor penetration of light into the higher depths of the cultures, which subsequently result in low biomass concentrations (typically 300–500 mg/L of dry mass) [1]. To overcome this limitation, microalgal/cyanobacterial cultivation could be performed under mixotrophic mode, where organic molecules, such as glucose, acetate, glycerol etc. Microalgal/cyanobacterial cultivation could be performed under mixotrophic mode, where organic molecules, such as glucose, acetate, glycerol etc. could be utilized as an energy and/or carbon source

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