Abstract
G. sulphuraria is a polyextremophilic microalga that can tolerate low pH, high temperature and high osmotic pressure. We cultivated G. sulphuraria ACUF 064 in chemostat at a biomass concentration of 134 to 243 g·m−2 aiming for maximal pigment content without compromising biomass productivity. Autotrophy was compared to ‘oxygen balanced’ mixotrophy with intracellular recirculation of oxygen and carbon dioxide. No differences were found in C-phycocyanin (C-PC) and protein content between autotrophic and mixotrophic cultures. In mixotrophy the biomass productivity and concentration were doubled compared to the photoautotrophic counterpart. In mixotrophy aeration was not needed and 89% of the substrate carbon was converted into biomass.Mixotrophically grown biomass contained 10% w/w C-PC which, combined with its high areal biomass productivity (49 g·m−2·day−1), sums up as one of the highest C-PC areal productivities ever reported (5 g·m−2·day−1) under 24 h/24 h illumination. C-PC extracted from G. sulphuraria was more stable than the currently used C-PC extracts from Spirulina. No significant loss of color was observed down to a pH of 3 and up to a temperature of 55 °C. G. sulphuraria had a protein content of 62% w/w and compared favorably with FAO dietary recommendation of adults regarding amino acid composition. G. sulphuraria contains a high proportion of essential, sulfur amino acids compared to Chlorella, Spirulina and soybean protein.Due to its attractive amino acid profile and high protein content, G. sulphuraria is a good candidate for food and feed applications to overcome sulfur amino acid deficiencies. In addition, oxygen balanced mixotrophy allows for efficient and productive cultivation of G. sulphuraria biomass.
Highlights
Galdieria sulphuraria is a polyextremophilic microalgae able to tolerate low pH [1], high temperature [2] and high osmotic pressure [3]
We previously demonstrated that G. sulphuraria can be successfully cultivated without any gas exchange by making use of oxygen balanced mixotrophy [1]
Chemostat production of G. sulphuraria ACUF 064 at biomass con centration higher than 4 g⋅L− 1 proved to be a successful strategy for constant biomass production with high pigment content both under autotrophic and mixotrophic conditions
Summary
Galdieria sulphuraria is a polyextremophilic microalgae able to tolerate low pH (as low as 0.2) [1], high temperature (up to 57 ◦C) [2] and high osmotic pressure (up to 400 g⋅L− 1 of sugar and 2–3 M of salt) [3]. Due to these exceptional traits, G. sulphuraria is often the only or ganism able to colonize acidic hot springs where it forms mats of deep blue-green color [4]. Compared to the C-PC extracted from Spirulina, C-PC extracted from Galdieria has shown greater stability at low pH and at high temperature, increasing the possible industrial applications of this pigment [11,12]
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