Physiological response and photosynthetic modeling of a Dactylococcus microalga during mixotrophic cultivation on glycerol

Grama, Borhane Samir;Chader, Samira;Khelifi, Douadi;Agathos, Spiros N.;Jeffryes, Clayton
(2014) 4th International Conference on Algal Biomass, Biofuels and Bioproducts — Location: Santa Fe, New Mexico, United States (15.June.2014)

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  • Grama, Borhane SamirUCLouvain
    Author
  • Chader, SamiraAlgerian Center of Renewable Energy (Centre de Développement des Energies Renouvelables), Unité de Développement des Equipements Solaires (UDES), Bou-Ismail, 42415 W. Tipaza, Algeria
    Author
  • Khelifi, DouadiLaboratory of Genetic Biochemistry and Plant Biotechnology, Faculty of Nature and Life Sciences, Université Constantine 1, Constantine, Algeria
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  • Agathos, Spiros N.orcid-logoUCLouvain
    Author
  • Jeffryes, ClaytonUCLouvain
    Author
Abstract
Introduction Dactylococcus dissociatus, a canthaxanthin, astaxanthin and adonixanthin producing microalga isolated from the Algerian Sahara, was characterized for its ability to be grown mixotrophically on glycerol. A novel method combing oximetry, PAM fluorometry and mixotrophic growth stoichiometry was used to predict rates of photosynthesis, respiration, substrate consumption and growth for the purpose of optimizing biomass productivity in the first stage of a two-stage process for the production of high-valued carotenoids in a photosynthetic biorefinery. Methods Cell cultures of D. dissociatus were grown at four different glycerol concentrations (0, 6, 30 and 150 mM) and were analysed for chlorophyll, carotenoids, lipids, dry cell weight, CHON composition, rate of oxygen exchange and for photosynthetic efficiency by variable fluorescence. Analytical measurements combined with resolving the stoichiometric matrix for biomass production under mixotrophic growth conditions were used to model the rates of photosynthesis, respiration and growth as a function of glycerol concentration and light intensity. Results Mixotrophic cultivation on glycerol increased biomass productivity, but had little effect on the mass fraction of lipids or carotenoids in the biomass. The respiration rate was observed to be uncoupled to the light intensity and even though glycerol inhibited photosynthesis the overall biomass productivity was higher in the mixotrophic cultures. The variable fluorescence and chlorophyll content were used to accurately predict the cell culture oxygen concentration and to close the stoichiometric mass balances in a system with simultaneous fermentation and photosynthesis, even in an underdetermined system. Conclusion Glycerol can be used to increase the biomass productivity of D. dissociatus, but does not increase the intracellular concentration of lipids or carotenoids. However, physiological insights gained from fermentive and photosynthetic modelling can be used to optimize a bioprocess for the production of biomass in the initial stage of a two-step bioprocess for the production of high-valued carotenoids.
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Grama, B. S., Chader, S., Khelifi, D., Agathos, S. N., & Jeffryes, C. (2014). Physiological response and photosynthetic modeling of a Dactylococcus microalga during mixotrophic cultivation on glycerol. 4th International Conference on Algal Biomass, Biofuels and Bioproducts, Santa Fe, New Mexico, United States. https://hdl.handle.net/2078.5/214822