Modelling of growth and accumulation of carotenoids in Haematococcus pluvialis as a function of irradiance and nutrients supply

This paper analyzes the feasibility of the autotrophic production of vegetative cells of Haematococcus pluvialis under conditions resembling outdoors. The experimental design simulates in laboratory with artificial light an outdoors circadian cycle similar to solar illumination. The influence of the irradiance and nutrient concentration on the growth rate and carotenoids accumulation in batch cultures is studied. The cultures were not photoinhibited even under the maximum irradiance-level tested (2500 μE m−2 s−1). Growth was kept nutrient-limited by using nutrients concentration below the standard inorganic medium (10 mM nitrate). When no nutrient-limitation occurs, the growth rate and biomass productivity measured 0.57 day−1 and 0.28 g L−1 day−1, respectively, were similar to the maximum values reported, regardless of the nutritional regime: autotrophic, mixotrophic or heterotrophic. On the other hand, carotenogenesis was only observed under nutrient-limiting conditions when the medium strength was reduced to 0.2- or 0.3-fold of the standard medium. On the other hand, carotenogenesis ceased under severe nutrient deprivation (i.e. nutrient strength of 0.1-fold of the standard medium). The growth rate and the carotenoids accumulation rate were demonstrated to be a function of the average irradiance inside the culture, and of the nutrient content of the medium. A mathematical model for the observed behaviour is proposed. This model was adequate to fit all the experimental data obtained. The values determined for the characteristics parameters are in agreement with those found by other authors. Therefore, the proposed model can be a useful tool for the design and management of Haematococcus cultures, and could allow improving the yield of this production process.