Abstract
In the current study, corn steep liquor (CSL) is evaluated as an ideal raw agro-material for efficient lipid and docosahexaenoic acid DHA production by Aurantiochytrium sp. Low CSL level in medium (nitrogen deficiency) stimulated the biosynthesis of lipids and DHA while inhibiting cellular growth. The transcriptomic profiles of the Aurantiochytrium sp. cells are analyzed and compared when cultured under high (H group), normal (N group), and low (L group) levels of CSL in the medium. The discriminated transcriptomic profiles from the three groups indicates that changes in CSL level in medium result in a global change in transcriptome of Aurantiochytrium sp. The overall de novo assembly of cDNA sequence data generated 61,163 unigenes, and 18,129 of them were annotated in at least one database. A total of 5105 differently expressed (DE) genes were found in the N group versus the H group, with 2218 downregulated and 2887 upregulated. A total of 3625 DE genes were found in the N group versus the L group, with 1904 downregulated and 1721 upregulated. The analysis and categorization of the DE genes indicates that the regulation mechanism of CSL involved in the perception and transduction of the limited nitrogen signal, the interactions between the transcription factors (TFs) and multiple downstream genes, and the variations in downstream genes and metabolites, in sequence, are illuminated for the first time in the current study.
Highlights
Corn steep liquor (CSL) is a major by-product of the corn wet milling industry
Yield and content reached the highest level (66.3% of biomass, 7.2 g/L and 66% of TFA) when the concentration of corn steep liquor (CSL) reached to 5 g/L with a C/N value of up to 12
The proline, lysine, and citrate derived from the TCA pathway increased with increases of the CSL of each medium. These results indicate that the nitrogen-rich medium could promote more carbon flux into the TCA cycle and enforce amino acid and protein synthesis in Aurantiochytrium sp. for cellular growth
Summary
Corn steep liquor (CSL) is a major by-product of the corn wet milling industry. Because it is rich in organic nitrogen, it has been used as a crucial nitrogen resource in microbial fermentation of products such as amino acids, polypeptides, and proteins. CSL has been utilized in the fermentation process as a nutritional and functional supplement due to its high content of vitamins, which make a significant contribution to nutrition. CSL has a much lower price as a bulk agro-industrial by-product than traditional nitrogen resources such as yeast extract and peptone, which. CSL has been used as a potential nitrogen resource in the microbial fermentations of various organic acids and other products [1,2]. DHA serves as a multi-function supplement and has been widely applied in the food, medical, and feed industries
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