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Abstract: Mixotrophy can be exploited to support algal growth over night or in dark-zones of a photobioreactor. In order to achieve the maximal productivity, however, it is fundamental also to provide CO2 in excess to maximize photosynthetic activity and phototropic biomass production. The aim of this paper is to verify the possibility of exploiting mixotrophy in combination with excess CO2. Two species with high biomass productivity were selected, Nannochloropsis salina and Chlorella protothecoides. Different organic substrates available at industrial scale were tested, and glycerol chosen for its ability to support growth of both species. In mixotrophic conditions, excess CO2 stimulated photosynthesis but blocked the metabolization of the organic substrate, thus canceling the advantages of mixotrophy. By cultivating microalgae under day–night cycle, organic substrate supported growth during the night, but only if CO2 supply was not provided. This represents thus a possible method to reconcile CO2 stimulation of photosynthesis with mixotrophy. [Copyright &y& Elsevier]

Abstract: Algae are interesting potential sources of biodiesel, although research is still needed to develop efficient large scale productions. One major factor affecting productivity is light use efficiency. The effect of different light regimes on the seawater alga Nannochloropsis gaditana was accessed monitoring growth rate and photosynthetic performances. N. gaditana showed the capacity of acclimating to different light intensities, optimizing its photosynthetic apparatus to illumination. Thanks to this response, N. gaditana maintained similar growth rates under a wide range of irradiances, suggesting that this organism is a valuable candidate for outdoor productions in variable conditions. In the conditions tested here, without external CO2 supply, light intensity alone was not found to be a major signal affecting lipids accumulation showing the absence of a direct regulatory link between the light stress and lipids accumulation. Strong illumination can nevertheless indirectly influences lipid accumulation if combined with other stresses or in the presence of excess CO2. [Copyright &y& Elsevier]

Mixotrophy can be exploited to support algal growth over night or in dark-zones of a photobioreactor. In order to achieve the maximal productivity, however, it is fundamental also to provide CO(2) in excess to maximize photosynthetic activity and phototropic biomass production. The aim of this paper is to verify the possibility of exploiting mixotrophy in combination with excess CO(2). Two species with high biomass productivity were selected, Nannochloropsis salina and Chlorella protothecoides. Different organic substrates available at industrial scale were tested, and glycerol chosen for its ability to support growth of both species. In mixotrophic conditions, excess CO(2) stimulated photosynthesis but blocked the metabolization of the organic substrate, thus canceling the advantages of mixotrophy. By cultivating microalgae under day-night cycle, organic substrate supported growth during the night, but only if CO(2) supply was not provided. This represents thus a possible method to reconcile CO(2) stimulation of photosynthesis with mixotrophy., (Copyright © 2011 Elsevier Ltd. All rights reserved.)