Neochloris oleoabundans is worth its salt: Transcriptomic analysis under salt and nitrogen stress

Abstract

Neochloris oleoabundans is an oleaginous microalgal species that can be cultivated in fresh water as well as salt water. Using salt water gives the opportunity to reduce production costs and the fresh water footprint for large scale cultivation. Production of triacylglycerols (TAG) usually includes a biomass growth phase in nitrogen-replete conditions followed by a TAG accumulation phase under nitrogen-deplete conditions. This is the first report that provides insight in the saline resistance mechanism of a fresh water oleaginous microalgae. To better understand the osmoregulatory mechanism of N. oleoabundans during growth and TAG accumulating conditions, the transcriptome was sequenced under four different conditions: fresh water nitrogen-replete and -deplete conditions, and salt water (525 mM dissolved salts, 448mM extra NaCl) nitrogen-replete and -deplete conditions. In this study, several pathways are identified to be responsible for salt water adaptation of N. oleoabundans under both nitrogen-replete and -deplete conditions. Proline and the ascorbate-glutathione cycle seem to be of importance for successful osmoregulation in N. oleoabundans. Genes involved in Proline biosynthesis were found to be upregulated in salt water. This was supported by Nuclear magnetic resonance (NMR) spectroscopy, which indicated an increase in proline content in the salt water nitrogen-replete condition. Additionally, the lipid accumulation pathway was studied to gain insight in the gene regulation in the first 24 hours after nitrogen was depleted. Oil accumulation is increased under nitrogen-deplete conditions in a comparable way in both fresh and salt water. The mechanism behind the biosynthesis of compatible osmolytes can be used to improve N. oleoabundans and other industrially relevant microalgal strains to create a more robust and sustainable production platform for microalgae derived products in the future.

Selective and mild fractionation of microalgal proteins and pigments using aqueous two‐phase systems

“…However, the disrupted microalgae added to the systems contained other biomolecules, such as pigments, lipids, carbohydrates and other proteins apart from Rubisco. The overall composition of microalgae is influenced by cultivation conditions . Microalgae cultivated in freshwater has higher amount of proteins and pigments than microalgae cultivated under saline conditions.…”

“…The overall composition of microalgae is influenced by cultivation conditions. 53 Microalgae cultivated in freshwater has higher amount of proteins and pigments than microalgae cultivated under saline conditions. When using N. oleoabundans cultivated in freshwater more proteins were concentrated in the interface [ Fig.…”

Stressing Algae for Biofuel Production: Biomass and Biochemical Composition of Scenedesmus dimorphus and Selenastrum minutum Grown in Municipal Untreated Wastewater

“…According to (Rao et al, 2007), high salinity can stimulate accumulation of intracellular lipids in microalgae. In a recent study dealing with Neochloris oleoabundans under salt and nitrogen stress, it has been shown that proline and the ascorbate-glutathione cycle play a key role for successful osmoregulation under salt stress; furthermore two genes such as glycerol-3-phosphate acyltransferase and glycerol-3-phosphate dehydrogenase where identified as promising targets to enhance TAG production (de Jaeger et al, 2018). Hence a possible explanation of our results is that under the stresses studied in S. dimorphus glycerol-3-phosphate dehydrogenase and glycerol-3-phosphate dehydrogenase are regulated in a way that the carbohydrate accumulation is reduced while lipid accumulation is stimulated as shown in Figure 1.…”

Delineating the molecular responses of a halotolerant microalga using integrated omics approach to identify genetic engineering targets for enhanced TAG production

“…Accumulation of antioxidant enzymes, osmolytes, and osmoprotectant molecules has been reported in Neochloris oleoabundans and Chlorella sp. S30, when cultivated under NaCl stress [15, 17].…”