Polyunsaturated fatty acids (PUFAs) have been widely applied in the food and medical industry. In this study, malonyl-CoA: ACP transacylase (MAT) was overexpressed through homologous recombination to improve PUFA production in Schizochytrium. The results showed that the lipid and PUFA concentration were increased by 10.1 and 24.5% with MAT overexpression, respectively. Metabolomics analysis revealed that the intracellular tricarboxylic acid cycle was weakened and glucose absorption was accelerated in the engineered strain. In the mevalonate pathway, intracellular carotene content was decreased, and the carbon flux was then redirected toward PUFA synthesis. Furthermore, a glucose fed-batch fermentation was finally performed with the engineered Schizochytrium. The total lipid yield was further increased to 110.5 g/L, 39.6% higher than the wild strain. Docosahexaenoic acid and eicosapentaenoic acid yield were enhanced to 47.39 g/L and 1.65 g/L with an increase of 81.5 and 172.5%, respectively. This study provided an effective metabolic engineering strategy for industrial PUFA production.
The preconditioned iterative solvers for solving Sylvester tensor equations are considered in this paper. By fully exploiting the structure of the tensor equation, we propose a projection method based on the tensor format, which needs less flops and storage than the standard projection method. The structure of the coefficient matrices of the tensor equation is used to design the nearest Kronecker product (NKP) preconditioner, which is easy to construct and is able to accelerate the convergence of the iterative solver. Numerical experiments are presented to show good performance of the approaches.National Natural Science Foundation of China [10961010]; Science and Technology Foundation of Guizhou Province [LKS[2009]03
White spot syndrome virus (WSSV) is a lethal pathogen of shrimp and many other crustaceans, including crayfish. However, the molecular mechanism underlying its cellular entry remains elusive due to the lack of shrimp cell lines for viral propagation. Crayfish hematopoietic tissue (Hpt) cell culture was recently established as a good model for WSSV infection study. Here, we showed that multiple endocytic routes, including clathrin-mediated endocytosis (CME), macropinocytosis and caveolae-mediated endocytosis, were indispensably employed for the viral entry into Hpt cell of the crayfish Cherax quadricarinatus. Intriguingly, cellular autophagic activity was positively correlated with efficient viral entry, in which a key autophagy-related protein, γ-aminobutyric acid receptor-associated protein (Cq-GABARAP), that not only localized but also co-localized with WSSV on the Hpt cell membrane, strongly facilitated WSSV entry by binding to the viral envelope VP28 in a CME-dependent manner that was negatively regulated by Cq-Rac1. Furthermore, cytoskeletal components, including Cq-β-tubulin and Cq-β-actin, bound to both recombinant rCq-GABARAP and WSSV envelope proteins, which likely led to viral entry promotion via cooperation with rCq-GABARAP. Even under conditions that promoted viral entry, rCq-GABARAP significantly reduced viral replication at an early stage of infection, which was probably caused by the formation of WSSV aggregates in the cytoplasm.
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