Exploration of the Hepatoprotective Effect and Mechanism of Swertia mussotii Franch in an Acute Liver Injury Rat Model.

BACKGROUND AND OBJECTIVE: Swertia mussotii Franch, also known as "Zangyinchen", is one of a Tibetan traditional herb used for treatment of liver diseases over thousands of years at Qinghai-Tibet Plateau, has been confirmed to be hepatoprotective. However, the underlying mechanism is largely unknown. MATERIALS AND METHODS: In this study, we evaluated the effect of S. mussotii treatment in a carbon tetrachloride-induced acute liver injury rat model by examining the serum alanine aminotransferase, aspartate aminotransferase, total bilirubin levels and performing histological observations of the liver tissues. Meanwhile, the metabolomics analysis was used to explore the molecular mechanism of S. mussotii treatment by high performance liquid chromatography tandem mass spectrometry. RESULTS: The results showed that S. mussotii treatment could effectively improve the serum alanine aminotransferase, aspartate aminotransferase, total bilirubin in acute liver injury rat model. Histological observation showed that S. mussotii treatment could effectively alleviate liver injury. Moreover, the metabolomics analysis showed that S. mussotii treatment could normalize the levels of many fatty acid metabolism related metabolites. And the results of pathway analysis showed that these metabolites significantly enriched in fatty acid biosynthesis pathway (myristic acid, dodecanoic acid and capric acid) and linoleic acid metabolism pathway (13-OxoODE). CONCLUSION: The results indicated that S. mussotii treatment could significantly improve acute liver injury through affecting the pathways related to lipid metabolism.

The improved L-tryptophan production in recombinant Escherichia coli by expressing the polyhydroxybutyrate synthesis pathway.

Polyhydroxybutyrate (PHB), the best known polyhydroxyalkanoates (PHA) has been believed to change intracellular metabolic flow and oxidation/reduction state, as well as enhance stress resistance of the host. In this study, a PHB biosynthesis pathway, which contains phaCAB operon genes from Ralstonia eutropha, was introduced into an L-tryptophan producing Escherichia coli strain GPT1002. The expression of the PHB biosynthesis genes resulted in PHB accumulation inside the cells and improved the L-tryptophan production. Quantitative real-time PCR analysis showed that the transcription of tryptophan operon genes in GPT2000 increased by 1.9 to 4.3 times compared with the control, indicating that PHB biosynthesis in engineered E. coli changed the physiological state of the host. Xylose was added into the medium as co-substrate to enhance the precursor supply for PHB biosynthesis. The addition of xylose improved both extracellular L-tryptophan production and intracellular PHB accumulation. Moreover, we obtained 14.4 g l(-1) L-tryptophan production and 9.7 % PHB (w/w) accumulation in GPT2000 via fed-batch cultivation.

Engineering of an N-acetylneuraminic acid synthetic pathway in Escherichia coli.

N-acetylneuraminic acid (NeuAc) has recently drawn much attention owing to its wide applications in many aspects. Besides extraction from natural materials, production of NeuAc was recently focused on enzymatic synthesis and whole-cell biocatalysis. In this study, we designed an artificial NeuAc biosynthetic pathway through intermediate N-acetylglucosamine 6-phosphate in Escherichia coli. In this pathway, N-acetylglucosamine 2-epimerase (slr1975) and glucosamine-6-phosphate acetyltransferase (GNA1) were heterologously introduced into E. coli from Synechocystis sp. PCC6803 and Saccharomyces cerevisiae EBY100, respectively. By derepressing the feedback inhibition of glucosamine-6-phosphate synthase, increasing the accumulation of N-acetylglucosamine and pyruvate, and blocking the catabolism of NeuAc, we were able to produce 1.62 g l⁻¹ NeuAc in recombinant E. coli directly from glucose. The NeuAc yield reached 7.85g l⁻¹ in fed-batch fermentation. This process offered an efficient fermentative method to produce NeuAc in microorganisms using glucose as carbon source and can be optimized for further improvement.

One-step of tryptophan attenuator inactivation and promoter swapping to improve the production of L-tryptophan in Escherichia coli.

BACKGROUND: L-tryptophan is an aromatic amino acid widely used in the food, chemical and pharmaceutical industries. In Escherichia coli, L-tryptophan is synthesized from phosphoenolpyruvate and erythrose 4-phosphate by enzymes in the shikimate pathway and L-tryptophan branch pathway, while L-serine and phosphoribosylpyrophosphate are also involved in L-tryptophan synthesis. In order to construct a microbial strain for efficient L-tryptophan production from glucose, we developed a one step tryptophan attenuator inactivation and promoter swapping strategy for metabolic flux optimization after a base strain was obtained by overexpressing the tktA, mutated trpE and aroG genes and inactivating a series of competitive steps. RESULTS: The engineered E. coli GPT1002 with tryptophan attenuator inactivation and tryptophan operon promoter substitution exhibited 1.67 ~ 9.29 times higher transcription of tryptophan operon genes than the control GPT1001. In addition, this strain accumulated 1.70 g l(-1) L-tryptophan after 36 h batch cultivation in 300-mL shake flask. Bioreactor fermentation experiments showed that GPT1002 could produce 10.15 g l(-1) L-tryptophan in 48 h. CONCLUSIONS: The one step inactivating and promoter swapping is an efficient method for metabolic engineering. This method can also be applied in other bacteria.

Extending homologous sequence based on the single gene mutants by one-step PCR for efficient multiple gene knockouts.

Multiple gene knockouts play an important role in metabolic engineering. The flanked homology length, homologous to the region adjacent to the target gene, of the knockout fragments has a great effect on the efficiency of multiple gene knockouts, whereas the existing gene knockout methods can only supply a very short homology. This article presents a strategy of easily extending homologous sequence based on the available strain library through one-step PCR amplification (the one-step PCR method). In this approach, the library of single gene mutants was used as the templates for PCR to amplify knockout fragments. Thus, the flanked homology can be extended as long as possible by designing primers upstream and downstream far from the target gene. Based on the one-step PCR method, we studied the effect of the homology length and the number of mutations on the efficiency of multiple gene knockouts. Our results indicated that the one-step PCR method permitted rapid and efficient construction of multiple mutants continuously or simultaneously, and a length of 200-300 bp homologous sequence was equal for multiple gene knockouts.

Production of succinate and polyhydroxyalkanoate from substrate mixture by metabolically engineered Escherichia coli.

The strategic design of this study aimed at producing succinate and polyhydroxyalkanoate (PHA) from substrate mixture of glycerol/glucose and fatty acid in Escherichia coli. To accomplish this, an E. coli KNSP1 strain derived from E. coli LR1110 was constructed by deletions of ptsG, sdhA and pta genes and overexpression of phaC1 from Pseudomonas aeruginosa. Cultivation of E. coli KNSP1 showed that this strain was able to produce 21.07 g/L succinate and 0.54 g/L PHA (5.62 wt.% of cell dry weight) from glycerol and fatty acid mixture. The generated PHA composed of 58.7 mol% 3-hydroxyoctanoate (3HO) and 41.3 mol% 3-hydroxydecanoate (3HD). This strain would be useful for complete utilization of byproducts glycerol and fatty acid of biodiesel production process.

Production of lactate in Escherichia coli by redox regulation genetically and physiologically.

Escherichia coli grows fermentatively in glucose-containing medium under anaerobic condition with formation of a mixture of organic acids (lactate, acetate, formate, and succinate) and ethanol to accommodate reducing equivalents generated during glycolysis. In this paper, we tried to improve the lactate accumulation in E. coli by redox regulation genetically and physiologically. Our results indicated that genetic regulation of the host by reducing the reductive by-product may improve the lactate production. In addition, lactate accumulation was also improved under reduced and anaerobic cultivation conditions. Engineered E. coli SDU4 was able to accumulate lactate under strictly anaerobic conditions to 100 g/L with a yield of 1.97 mol/mol glucose.

Engineering Escherichia coli for an efficient aerobic fermentation platform.

Acetate, as a major by-product, was excreted by Escherichia coli when aerobic fermentation runs at high growth rates. In order to reduce the acetate secretion during the fermentation fundamentally, a list of genes related to acetate accumulation in E. coli was selected and knocked out. Physiological characterization of each mutant demonstrated that the growth and metabolites accumulation properties of these mutations exhibited significant change upon pathway engineering. The final engineered E. coli QZ1110 with ptsG, poxB, pta and iclR gene mutations was confirmed to accumulate 270% more biomass with 90% less acetate secretion than that of wild type E. coli in LB medium supplied with 1% glucose. Polyhydroxybutyrate biosynthesis experiment showed that the acetate reduction of the engineered strain in minimal medium also reduced 90% while the PHB accumulation increased almost 100% compare to wild type E. coli.