EFFECTS OF CULTURE CONDITIONS ON PHYTOSTEROL CONTENT OF SELECTED MICROALGAE SPECIES AND THE DEVELOPMENT OF A CHLOROPHYLL-BASED RAPID SCREENING PIPELINE

Abstract

This work investigated the potential of four microalgae species, including the haptophyte Diacronema lutheri, Eustigmatophyte Nannochloropsis oculata and the diatoms Phaeodactylum tricornutum and Chaetoceros muelleri, for the sustainable production of sterols. In industrial settings, microalgae cultivation conditions are typically optimized for maximum metabolite production and cost savings. Hence, the first study in this work explored the effects of light intensity on the sterol profile and concentration of cultures harvested at different growth phases. In most cases, cultures grown at medium light level and harvested in stationary phase had the greatest sterol concentration with few exceptions. Notably, Diacronema lutheri had the highest diversity of sterol structures amongst all the species investigated. In the second study, the potential of chlorophyll as a proxy tool to rapidly estimate sterol production was investigated. The results showed that sterol to chlorophyll ratio (Str/Chl) has potential to be used as a coarse estimation tool for sterol concentration in diatoms because of limited intra-species variability. The ratio was however limited in estimating sterol concentration across taxa due to large inter-species variability. The last study explored the effect of lactose as a carbon source on sterols in the mixotrophic cultivation of Diacronema lutheri. The relative abundance of the individual sterol structures of Diacronema lutheri was impacted by lactose supplementation but not the total sterol concentration. Overall, this work has provided valuable insights into the relationship between chlorophyll and sterol and its use in rapid selection high sterol yielding strains. Additionally, this work demonstrated the metabolic plasticity of microalgae species and how that could be adapted in biotechnological settings for sterol production using various culture conditions.