Abstract
Cultivation of Spirulina platensis in Zarrouk media containing 0–20 g l-1 glucose was studied in a photobioreactor for 30 days using a light intensity of 3 klux. Various parameters were measured to evaluate the enhancement of cell performance with glucose such as cell number, osmolarity, membrane stability, biomass productivity, doubling time, stress intensity, stress tolerance, chlorophyll, protein, carbohydrates, and lipid contents. Based on the results, we concluded that S. platensis is able to grow and produce some ingredients in Zarrouk media containing up to 20 g l-1 of glucose which is the first to be reported. The cell concentration of the mixotrophic cultures (80 cells per mm2) corresponded well to the sum of the autotrophic cell concentrations (50 cells per mm2), showing that the addition of carbohydrate positively effects on the microalgae growth. The continuous operation supplemented with 0.5 g l-1 of glucose (G0.5) led to the maximum cell concentration about 9.06 g l-1 wet and 1.32 g l-1 dry weights. The highest tolerance index, specific growth rate, biomass productivity, cell division, osmolarity and membrane stability index were respectively 102.5%, 0.15 d-1, 0.04 g l-1d-1, 0.26 div d-1, 0.87 osmol kg-1 and 93.8%, obtained in the same treatment. Chlorophyll (6.7 % in G0; 0.046 g l-1 in G0.5), protein (79.9 % and 0.884 g l-1 in G0.5), carbohydrates (55.5% in G20; 0.492 g l-1 in G6) and lipid (53.3% in G10; 0.636 g l-1 in G0) percentages and yields were mostly enhanced in the mixotrophic condition. This study indicated that mixotrophic growth of S. platensis is useful for commercial biomass production.
Highlights
Formulation of the problemLarge-scale microalgal production has been studied for decades [1,2], given the wide variety of practical and potential metabolic products under different cultivation conditions
The objectives of this work were to analyze the feasibility of the use of organic carbon source as a supplement in a modified culture medium and its influence on the mixotrophic growth, metabolites amount and composition of S. platensis
The algae were cultured in a photobioreactor using a mineral growth medium supplemented with 10 different concentrations of glucose
Summary
Formulation of the problemLarge-scale microalgal production has been studied for decades [1,2], given the wide variety of practical and potential metabolic products under different cultivation conditions. Under autotrophic cultivation (in the light), the cells harvest light energy and use CO2 as a carbon source This organism has been found to utilize organic carbon substrates (i.e. glucose) for heterotrophic growth [4]. The accessible light and carbon source as a dual limiting process might upgrade the yield [6] up to a limitation of massive growth and dense population. This way the biofixation potentially combines the capture of carbon from CO2 and carbohydrate molecule, building a promising road for mitigation of greenhouse gas emissions, environmental impacts and cultivation costs
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