Production of ginsenoside compound K by microbial cell factory using synthetic biology-based strategy: a review.

Ginsenoside compound K (CK) is a major intestinal bacterial metabolite of the protopanaxadiol-type ginsenoside family that can be absorbed in the systemic circulation. CK possesses diverse and important pharmacological properties. The low production and high cost of traditional manufacturing methods based on the extraction and biotransformation of total ginsenosides from ginseng have limited their medical application. However, considerable progress has been made in the area of de novo CK production via microbial cell factories using synthetic biology-based strategies. By introducing key enzymes responsible for CK biosynthesis into microbial cells, CK was produced via a series of in vivo enzymatic reactions that utilize the inherent precursors in microbial cells. After systematic optimization using various metabolic engineering strategies, the yield of CK increased significantly and exceeded the traditional plant extraction-biotransformation method, implying the commercial feasibility of this approach. This review summarizes recent novel advancements in the production of CK using microbial cell factories.

Efficient production of ε-poly-L-lysine by Streptomyces ahygroscopicus using one-stage pH control fed-batch fermentation coupled with nutrient feeding.

ε-Poly-L-lysine (ε-PL) is a homopolymer of L-lysine molecules connected between the ε amino and alpha carboxyl groups. This polymer is currently used as a natural preservative in food. Insufficient biomass is a major problem in ε-PL fermentation. Here, to improve cell growth and ε-PL productivity, various nitrogen-rich nutrients were supplemented into flask cultures after 16 h cultivation, marking the onset of ε-PL biosynthesis. Yeast extract, soybean powder, corn powder, and beef extract significantly improved cell growth. In terms of ε-PL productivity, yeast extract at 0.5% (w/v) gave the maximum yield (2.24 g/l), 115.4% higher than the control (1.04 g/l), followed by soybean powder (1.86 g/l) at 1% (w/v) and corn powder (1.72 g/l) at 1% (w/v). However, supplementation with beef extract inhibited ε-PL production. The optimal time for supplementation for all nutrients examined was at 16 h cultivation. The kinetics of yeast-extract-supplemented cultures showed enhanced cell growth and production duration. Thus, the most commonly used two-stage pH control fed-batch fermentation method was modified by omitting the pH 5.0-controlled period, and coupling the procedure with nutrient feeding in the pH 3.9-controlled phase. Using this process, by continuously feeding 0.5 g/h of yeast extract, soybean powder, or corn powder into cultures in a 30 L fermenter, the final ε-PL titer reached 28.2 g/l, 23.7 g/l, and 21.4 g/l, respectively, 91.8%, 61.2%, and 45.6% higher than that of the control (14.7 g/l). This describes a promising option for the mass production of ε-PL.

Hypoglycemic effects of Ganoderma lucidum polysaccharides in type 2 diabetic mice.

Our aims were to investigate the hypoglycemic effects and mechanisms of action of Ganoderma lucidum polysaccharides (GLPs) administered for 7 days in type 2 diabetic mice. The mice were randomly divided into four groups (8 mice/group): normal control group, diabetic control group, low-dose GLP-treated diabetic group (50 mg/kg/d), and high-dose GLP-treated diabetic group (100 mg/kg/d). Diabetes was induced by streptozotocin injection and high-fat dietary feeding. At the end of the study, fasting serum glucose, insulin, body weight (BW) and epididymal white adipose tissue weight were measured. The hepatic mRNA levels of glycogen phosphorylase (GP), fructose-1,6-bisphosphatase (FBPase), phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) genes were determined by real-time polymerase chain reaction. Both doses of GLPs significantly decreased fasting serum glucose, insulin and epididymal fat/BW ratio compared with the diabetic control group (p < 0.05). The hepatic mRNA levels of GP, FBPase, PEPCK and G6Pase were significantly lower in both GLP-treated groups compared with the diabetic control group. Taken together, GLPs significantly decrease fasting serum glucose levels in type 2 diabetic mice in a dose-dependent manner. The decreases in fasting serum glucose levels may be associated with decreased mRNA expression levels of several key enzymes involved in gluconeogenesis and/or glycogenolysis.