Metabolomic profiles of tropical Chlorella species in response to physiological changes during nitrogen deprivation

Chlorella species are known to be potential algal candidates for biodiesel production due to their ability to store lipids and their natural metabolic versatility. This study assessed the photosynthetic performance, biochemical composition, and metabolomic profiles of tropical Chlorella UMACC050 harvested from different growth phases in batch culture, grown under nitrogen-replete, and nitrogen-depleted conditions. Physiological data suggested that growth and photosynthetic efficiency were affected during nitrogen deprivation. Nitrogen deprivation resulted in a decrease in biomass productivity and an increase of lipid content. Nitrogen-depletion resulted in an increase in saturated fatty acids (SFA) and monounsaturated fatty acids (MUFA), especially C16:0, C18:0, and C18:1, at the expense of polyunsaturated fatty acids (PUFA). Changes in the metabolomic profiles suggested that there was nitrogen assimilation from proteins and photosynthetic machinery, together with repartitioning of carbon into carbohydrates and lipids in response to nitrogen depletion. Overall, our results expand the current understanding of metabolomics of Chlorella species and provide valuable insights into their lipid accumulation during nitrogen deprivation, which is important for optimization of lipid productivity in the tropical environment

Metabolomic profiles of tropical Chlorella and Parachlorella species in response to physiological changes during exponential and stationary growth phase

Chlorella species are known to be potential algal candidates for biodiesel production due to their ability to store high lipid content and their natural metabolic versatility. An understanding of physiology and metabolic capacity of indigenous Chlorella strains is potentially useful for future biodiesel production in the tropical environment. The primary aim of this study was to assess the photosynthetic performance, biochemical content and fatty acid composition of Chlorella and Parachlorella species grown and harvested during exponential (EX) and stationary (STA) growth phases in batch culture. Physiological data suggested that the cells responded to these conditions by initiating lipid accumulation when growing from EX to STA phase. An increase of lipid and saturated fatty acids (SFA) contents was observed in STA, although this trend was not consistent across the different strains of Chlorella and Parachlorella species. To gain further insights into metabolomic adaptation at different growth phases, metabolites were extracted from selected Chlorella and Parachlorella strains at EX and STA phase. These metabolic profiles were analysed resulting in identification of 74 metabolites. Metabolomic profiles of Parachlorella showed that there was an increase in recycling of amino acids and nucleic acids at STA phase. The metabolites associated with photosynthesis and chlorophyll biosynthesis were also repressed while carbon sources were channelled into lipid biosynthesis. Meanwhile, Chlorella species showed a similar response in carbon allocation for lipid accumulation with lesser influence on amino acid and chlorophyll degradation. Therefore, Chlorella and Parachlorella species exhibit different changes in metabolic responses at different growth phases, which may be the result of metabolic adaptations arising from their evolutionary plasticity. Overall, our results expand the current understanding of metabolomics of Chlorella and Parachlorella species and provide valuable insights into their lipid accumulation during different stages, which is important for optimization of lipid productivity for biodiesel production

Metabolic and physiological regulation of Chlorella sp. (Trebouxiophyceae, Chlorophyta) under nitrogen deprivation

A freshwater green microalgae Chlorella sp., UMACC344 was shown to produce high lipid content and has the potential to be used as feedstock for biofuel production. In this study, photosynthetic efficiency, biochemical profiles and non-targeted metabolic profiling were studied to compare between the nitrogen-replete and deplete conditions. Slowed growth, change in photosynthetic pigments and lowered photosynthetic efficiency were observed in response to nitrogen deprivation. Biochemical profiles of the cultures showed an increased level of carbohydrate, lipids and total fatty acids, while the total soluble protein content was lowered. A trend of fatty acid saturation was observed in the nitrogen-deplete culture with an increase in the level of saturated fatty acids especially C16:0 and C18:0, accompanied by a decrease in proportions of monounsaturated and polyunsaturated fatty acids. Fifty-nine metabolites, including amino acids, lipids, phytochemical compounds, vitamins and cofactors were significantly dysregulated and annotated in this study. Pathway mapping analysis revealed a rewiring of metabolic pathways in the cells, particularly purine, carotenoid, nicotinate and nicotinamide, and amino acid metabolisms. Within the treatment period of nitrogen deprivation, the key processes involved were reshuffling of nitrogen from proteins and photosynthetic machinery, together with carbon repartitioning in carbohydrates and lipids