Cultivation of the polyextremophileCyanidioschyzon merolae10D during summer conditions on the coast of the Red Sea and its adaptation to hypersaline sea water

Abstract

The west coast of Saudi Arabia borders the Red Sea, which maintains high average temperatures and increased salinity compared to other seas or oceans. Summer conditions in the Arabian Peninsula may exceed the temperature tolerance of most currently cultivated microalgae. The Cyanidiales are polyextremophilic red algae whose native habitats are at the edges of acidic hot springs. Cyanidioschyzon merolae 10D has recently emerged as an interesting model organism capable of high-cell density cultivation on pure CO2 with optimal growth at 42 degrees C and low pH between 0.5-2. C. merolae biomass has an interesting macromolecular composition, is protein rich, and contains valuable bio-products like heat-stable phycocyanin, carotenoids, beta-glucan, and starch. Here, photobioreactors were used to model C. merolae 10D growth performance in simulated environmental conditions of the mid-Red Sea coast across four seasons, it was then grown at various scales outdoors in Thuwal, Saudi Arabia during the Summer of 2022. We show that C. merolae 10D is amenable to cultivation with industrial-grade nutrient and CO2 inputs outdoors in this location and that its biomass is relatively constant in biochemical composition across culture conditions. We also show the adaptation of C. merolae 10D to high salinity levels of those found in Red Sea waters and conducted further modeled cultivations in nutrient enriched local sea water. It was determined that salt-water adapted C. merolae 10D could be cultivated with reduced nutrient inputs in local conditions. The results presented here indicate this may be a promising alternative species for algal bioprocesses in outdoor conditions in extreme desert summer environments.

Engineered ketocarotenoid biosynthesis in the polyextremophilic red microalgaCyanidioschyzon merolae10D

“…Our work indicates that C. merolae 10D could be cultivated outdoors, even in some of the hottest urban environments in the world during summer months, but life-cycle analysis would be required to determine whether the CAPEX required to build a controlled bioreactor with constant illumination would be more beneficial than simply using outdoor environmental conditions in situ. This is also encouraged by our recent finding that C. merolae can be adapted to be grown in acidified sea water salinities, further expanding its possible range of geographical application (Hirooka et al, 2020;Villegas et al, 2023). Indeed, each implementation of such a cultivation would require individual case-considerations.…”