Construction of an l-cysteine hyper-producing strain of Escherichia coli based on a balanced carbon and sulfur module strategy / 生物工程学报

l-cysteine is an important sulfur-containing α-amino acid. It exhibits multiple physiological functions with diverse applications in pharmaceutical cosmetics and food industry. Here, a strategy of coordinated gene expression between carbon and sulfur modules in Escherichia coli was proposed and conducted for the production of l-cysteine. Initially, the titer of l-cysteine was improved to (0.38±0.02) g/L from zero by enhancing the biosynthesis of l-serine module (serAf, serB and serCCg) and overexpression of CysB. Then, promotion of l-cysteine transporter, increased assimilation of sulfur, reduction or deletion of l-cysteine and l-serine degradation pathway and enhanced expression of cysEf (encoding serine acetyltransferase) and cysBSt (encoding transcriptional dual regulator CysB) were achieved, resulting in an improved l-cysteine titer (3.82±0.01) g/L. Subsequently, expressions of cysM, nrdH, cysK and cysIJ genes that were involved in sulfur module were regulated synergistically with carbon module combined with utilization of sulfate and thiosulfate, resulting in a strain producing (4.17±0.07) g/L l-cysteine in flask shake and (11.94±0.1) g/L l-cysteine in 2 L bioreactor. Our results indicated that efficient biosynthesis of l-cysteine could be achieved by a proportional supply of sulfur and carbon in vivo. This study would facilitate the commercial bioproduction of l-cysteine.

Study on Application of Electronic Tongue in the Evaluation of Taste-masking Effect of Pharmaceutical Formulation / 世界科学技术-中医药现代化

Taste-masking effect of pharmaceutical formulation is important for the pharmacy worker to carry out study on taste-masking of pharmaceutical formulation. This study discussed the feasibility of electronic tongue in the evaluation of taste-masking effect. The berberine hydrochloride was used as model drug of bitterness. Sodium cycla-mate, 2,4-Dihydroxybenzoic acid and sodium cyclamate were used as bitterness inhibitors. Through detection of elec-tronic tongue, results from principal component analysis (PCA), and indexes such as distance of bitterness (D), dis-tance of bitterness reduction, inhibition rate (Ir), the determination was given on whether results from the bitterness inhibition of berberine hydrochloride and taste results from volunteers were the same. In addition, sodium cyclamate, which was the best bitterness inhibition, was made into different concentrations in order to optimize its using dosage. The data analysis results showed that in the berberine hydrochloride solution with the concentration of 0.005 mg/mL, the ranking order of the bitterness-masking efficiency was sodium cyclamate > 2,4-Dihydroxybenzoic acid > sodium acetate anhydrous. Along with the increasing concentration of sodium cyclamate, the taste-masking effect is better. However, after the concentration level of 0.2%, the change on taste-masking effect was relatively small. In the prac-tical work, the concentration of sodium cyclamate can be selected at the level of 0.2%. This experiment effect was the same as the human taste results. This study showed that the electronic tongue may be a useful tool in the evalua-tion of taste-masking efficiency to some extent.

Study on Quantitation of Bitterness Intensity and Relationship between Bitterness Intensity & Concentration of Bitter Drug / 世界科学技术-中医药现代化

This paper was aimed to study the quantitation method of bitterness intensity of bitter drug, and to ex-plore the mutual relations between the bitterness intensity and the concentration of bitter drugs solution. The mod-el drug of berberine hydrochloride, which was made into a series of solutions of different concentrations, was ap-plied. Twenty volunteers, who were screened, trained and qualified, tasted the different concentration of aqueous solution, with the purpose of detecting the rank bitterness intensity. After analyzing the features of the data and testing the logarithm model and Weibull curve model, as well as nonlinear fitting, we finally set up the appropri-ate relationship curve between the concentration and the bitterness intensity. There is a good curve positive corre-lation between the bitterness intensity and the concentration, which is consistent with the Weibull curve model (R2= 0.9973, RMSE = 0.0976, RMSECV = 0.1453). The fitting degree of the model established in this paper is high, which provides a reference for quantitation and forecast of the drug bitterness.