Exploration of the Biotechnological Potential of Two Newly Isolated Haematococcus Strains from Reunion Island for the Production of Natural Astaxanthin

<i>Haematococcus lacustris</i> is a freshwater green microalgae species able to produce and accumulate astaxanthin in response to environmental stresses such as high light and nutrient deprivation. Astaxanthin is a xanthophyll carotenoid of growing economic interest due to its numerous biological activities, notably its strong antioxidant properties, which can be valued in the fields of nutrition, health, feed and aquaculture. The present study aims at evaluating the capacity of two newly isolated <i>Haematococcus</i> strains from the biodiversity of Reunion Island, to be cultivated in a photobioreactor and to produce astaxanthin. The results showed that both strains were able to grow in various nutritive media and to produce and accumulate astaxanthin in response to stresses, mainly in the form of astaxanthin monoesters, which represented up to 2% of the dry biomass weight and which were mostly composed of linoleic and linolenic acids. In fed-batch cultures using 3 L benchtop photobioreactors, the concentrations of biomass enriched in astaxanthin reached up to 3 g L^-1 (dry weight) with biomass productivities of 0.04 and 0.02 g L^-1 d^-1 based on the durations of the vegetative stage and of the entire culture, respectively. In these cultures, the astaxanthin productivities were found to reach on average around 0.25 mg L^-1 d^-1. Although these results were relatively low compared to the literature, the possibility of improving growth conditions in order to improve biomass and astaxanthin yields, to guarantee economic viability for cultivation at a commercial scale, was further discussed.