3-Dehydroshikimate (DHS) is a useful starting metabolite for the biosynthesis of muconic acid (MA) and shikimic acid (SA), which are precursors of various valuable polymers and drugs. Although DHS biosynthesis has been previously reported in several bacteria, the engineered strains were far from satisfactory, due to their low DHS titers. Here, we created an engineered Escherichia coli cell factory to produce a high titer of DHS as well as an efficient system for the conversion DHS into MA. First, the genes showing negative effects on DHS accumulation in E. coli, such as tyrR (tyrosine dependent transcriptional regulator), ptsG (glucose specific sugar: phosphoenolpyruvate phosphotransferase), and pykA (pyruvate kinase 2), were disrupted. In addition, the genes involved in DHS biosynthesis, such as aroB (DHQ synthase), aroD (DHQ dehydratase), ppsA (phosphoenolpyruvate synthase), galP (D-galactose transporter), aroG (DAHP synthase), and aroF (DAHP synthase), were overexpressed to increase the glucose uptake and flux of intermediates. The redesigned DHS-overproducing E. coli strain grown in an optimized medium produced ~117 g/L DHS in 7-L fed-batch fermentation, which is the highest level of DHS production demonstrated in E. coli. To accomplish the DHS-to-MA conversion, which is originally absent in E. coli, a codon-optimized heterologous gene cassette containing asbF, aroY, and catA was expressed as a single operon under a strong promoter in a DHS-overproducing E. coli strain. This redesigned E. coli grown in an optimized medium produced about 64.5 g/L MA in 7-L fed-batch fermentation, suggesting that the rational cell factory design of DHS and MA biosynthesis could be a feasible way to complement petrochemical-based chemical processes.
The hepatoprotective effects of fermented black rice bran extracts (FF1 and FF2: black rice bran fermented by Lentinus edodes derived from mycelium supplemented with soybean or Hovenia dulcis) and their associated mechanisms were evaluated. In an in vitro experiment, FFs caused significant amelioration of the metabolic function of rat hepatocytes treated with NH4Cl. In addition, administration of FFs to rats with chronic liver injury induced by 12-week continual alcohol consumption resulted in significant restoration of body weight shrinkage, notable attenuation of excessive aspartate aminotransferase, alkaline phosphatase and endotoxin in serum, malondialdehyde in liver and the lactulose/mannitol ratio in urine. Furthermore, FF1 or FF2 also caused significant downregulation of gene expression of several critical inflammatory mediators (interleukin-6, tumor necrosis factor-alpha, cyclooxygenase-2 and inducible nitric oxide synthase). Histopathological findings also indicated that FFs reduced inflammation, necrosis and fatty infiltration in liver tissue. Taken together, FFs exert hepatoprotective effects through anti-inflammatory and anti-lipid peroxidative properties and regulation of intestinal permeability.
PRACTICAL APPLICATIONSIn this study, mycelia fermentation was utilized as a feasible strategy for enhancing the hepatotherapeutic effect of black rice and herbs. The findings demonstrated that Hovenia dulcis exerts a synergistic protective effect on an alcoholic liver disease animal model and could provide a new effective potential approach to alleviate alcoholic liver diseases.
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