Nitrogen Starvation Enhances the Production of Saturated and Unsaturated Fatty Acids in Aurantiochytrium sp. PKU#SW8 by Regulating Key Biosynthetic Genes

Abstract

Nitrogen deprivation is known to improve lipid accumulation in microalgae and thraustochytrids. However, the patterns of fatty acid production and the molecular mechanisms underlying the accumulation of unsaturated and saturated fatty acids (SFAs) under nitrogen starvation remain largely unknown for thraustochytrids. In this study, batch culture experiments under nitrogen replete and nitrogen starvation conditions were performed, and the changes in the transcriptome of Aurantiochytrium sp. PKU#SW8 strain between these conditions were investigated. Our results showed improved yields of total fatty acids (TFAs), total unsaturated fatty acids, and total SFAs under nitrogen starvation, which suggested that nitrogen starvation favors the accumulation of both unsaturated and saturated fatty acids in PKU#SW8. However, nitrogen starvation resulted in a more than 2.36-fold increase of SFAs whereas a 1.7-fold increase of unsaturated fatty acids was observed, indicating a disproportionate increase in these groups of fatty acids. The fabD and enoyl-CoA hydratase genes were significantly upregulated under nitrogen starvation, supporting the observed increase in the yield of TFAs from 2.63 ± 0.22 g/L to 3.64 ± 0.16 g/L. Furthermore, the pfaB gene involved in the polyketide synthase (PKS) pathway was significantly upregulated under nitrogen starvation. This suggested that the increased expression of the pfaB gene under nitrogen starvation may be one of the explanations for the increased yield of docosahexaenoic acid by 1.58-fold. Overall, our study advances the current understanding of the molecular mechanisms that underlie the response of thraustochytrids to nitrogen deprivation and their fatty acid biosynthesis.

Comparative Genomic Analyses of Cellulolytic Machinery Reveal Two Nutritional Strategies of Marine Labyrinthulomycetes Protists

“…Filter paper and 1% CMC-Na were used as the substrates, respectively. The strains were first cultured in an M4 medium ( 92 ) at 28°C until the logarithmic growth phase to obtain seed cultures for quantification of cellulase activity. The seed culture (3 mL) was centrifuged at 4,000 rpm at 25°C for 10 min.…”

Marine thraustochytrid: exploration from taxonomic challenges to biotechnological applications

“…Early researchers improved intracellular lipid production by optimizing the fermentation conditions for thraustochytrids. They found that stress conditions such as low temperature (Ma et al, 2017), low or high dissolved oxygen (Sun et al, 2016;Heggeset et al, 2019) and nitrogen starvation (Chen et al, 2022) could stimulate the accumulation of intracellular lipids. Laboratory domestication and phased cultivation strategies (Wang et al, 2021a;Chen et al, 2022) have been developed.…”

“…They found that stress conditions such as low temperature (Ma et al, 2017), low or high dissolved oxygen (Sun et al, 2016;Heggeset et al, 2019) and nitrogen starvation (Chen et al, 2022) could stimulate the accumulation of intracellular lipids. Laboratory domestication and phased cultivation strategies (Wang et al, 2021a;Chen et al, 2022) have been developed. Additionally, the inclusion of lipase inhibitors (Orlistat) (Ma et al, 2021), antioxidants (Zhang et al, 2020) and plant hormones (Yu et al, 2016) in the culture medium can influence PUFAs metabolism and promote lipid accumulation.…”

Protist–Lactic Acid Bacteria Co-Culture as a Strategy to Bioaccumulate Polyunsaturated Fatty Acids in the Protist Aurantiochytrium sp. T66

“…Therefore, the use of these microorganisms has been widely proposed as a strategy to develop functional foods and feeding technology. Although many studies have shown that these protists are efficient in producing and accumulating PUFAs [ 16 , 17 , 18 , 19 ], the quantity produced is still not enough to cover the needs of the aquaculture industry [ 7 , 19 ]. Therefore, it is still necessary to optimize the production process in order to enrich the content of PUFAs in protists.…”