Background The oleaginous microorganism Schizochytrium sp. is widely used in scientific research and commercial lipid production processes. However, low glucose-to-lipid conversion rate (GLCR) and low lipid productivity of Schizochytrium sp. restrict the feasibility of its use. Results Orlistat is a lipase inhibitor, which avoids triacylglycerols (TAGs) from hydrolysis by lipase. TAGs are the main storage forms of fatty acids in Schizochytrium sp. In this study, the usage of orlistat increased the GLCR by 21.88% in the middle stage of fermentation. Whereas the productivity of lipid increased 1.34 times reaching 0.73 g/L/h, the saturated fatty acid and polyunsaturated fatty acid yield increased from 21.2 and 39.1 to 34.9 and 48.5 g/L, respectively, indicating the advantages of using a lipase inhibitor in microbial lipids fermentation. Similarly, the system was also successful in Thraustochytrid Aurantiochytrium. The metabolic regulatory mechanisms stimulated by orlistat in Schizochytrium sp. were further investigated using transcriptomics and metabolomics. The results showed that orlistat redistributed carbon allocation and enhanced the energy supply when inhibiting the TAGs’ degradation pathway. Therefore, lipase in Schizochytrium sp. prefers to hydrolyze saturated fatty acid TAGs into the β-oxidation pathway. Conclusions This study provides a simple and effective approach to improve lipid production, and makes us understand the mechanism of lipid accumulation and decomposition in Schizochytrium sp., offering new guidance for the exploitation of oleaginous microorganisms.

Escherichia coli, one of the most efficient expression hosts for recombinant proteins (RPs), is widely used in chemical, medical, food and other industries. However, conventional expression strains are unable to effectively express proteins with complex structures or toxicity. The key to solving this problem is to alleviate the host burden associated with protein overproduction and to enhance the ability to accurately fold and modify RPs at high expression levels. Here, we summarize the recently developed optimization strategies for the high-level production of RPs from the two aspects of host burden and protein activity. The aim is to maximize the ability of researchers to quickly select an appropriate optimization strategy for improving the production of RPs.

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It is well known that polyunsaturated fatty acids (PUFAs) in Schizochytrium sp. are mainly synthesized via the polyketide synthase (PKS) pathway. However, the specific mechanism of PKS in fatty acid synthesis is still unclear. In this work, the functions of ORFA, ORFB, ORFC, and their individual functional domain genes on fatty acid synthesis were investigated through heterologous expression in Yarrowia lipolytica. The results showed that the expression of ORFA, ORFB, ORFC, and their individual functional domains all led to the increase of the very long-chain PUFA content (mainly eicosapentaenoic acid). Furthermore, the transcriptomic analysis showed that except for the 3-ketoacyl-ACP synthase (KS) domain of ORFB, the expression of an individual functional domain, including malonyl-CoA: ACP acyltransferase, 3-hydroxyacyl-ACP dehydratase (DH), 3-ketoacyl-ACP reductase, and KS domains of ORFA, acyltransferase domains of ORFB, and two DH domains of ORFC resulted in upregulation of the tricarboxylic acid cycle and pentose phosphate pathway, downregulation of the triacylglycerol biosynthesis, fatty acid synthesis pathway, and β-oxidation in Yarrowia lipolytica. These results provide a theoretical basis for revealing the function of PKS in fatty acid synthesis in Y. lipolytica and elucidate the possible mechanism for PUFA biosynthesis.