Analysis of the infection and drug resistance of pathogenic bacteric in venous catheter / 国际检验医学杂志

Objective To investigate the hospital distribution and drug resistance of pathogens of venous catheter-related infec-tion,so as to provide basis for appropriate usage of antibiotics in clinic.Methods The culture and drug susceptibility results of 369 venous catheter were analyzed retrospectively from 2009 January to 2012 December.Results 161 strains of pathogens were detec-ted among 369 venous catheter,the positive rate was 43.6%.There were 83 strains of Gram positive bacteria,accounting for 51.6%,and Staphylococcus epidermidis had the highest positive rate.There were 63 strains of Gram negative bacteria,accounting for 39.1%,and Klebsiella pneumoniae and Bauman Acinetobacter were main isolated bacteria.There were 15 strains of Fungi,ac-counting for 9.3%,and Candida parapsilosis had the highest positive rate.There was none Gram positive bacteria resistant to van-comycin and linezolid.Carbapenems remained high activity against Gram negative bacteria.Conclusion Staphylococcus epidermidis and Klebsiella pneumoniae are mainly detected in venous catheter in the hospital infection.

Metabolic shift of Corynebacterium acetoacidophilum-deltaldh under oxygen deprivation conditions / 生物工程学报

Lactate and succinate were produced by Corynebacterium acetoacidophilum from glucose under oxygen deprivation conditions. To construct knockout mutant, lactate dehydrogenase gene (ldh) of C. acetoacidophilum was deleted by double-crossover chromosome replacement with sacB gene. Comparing with the wild strain ATCC13870, ldhA-deficent mutant produced no lactate with glucose consumption rate decreased by 29.3%, while succinate and acetate concentrations were increased by 45.6% and 182%, respectively. Moreover, the NADH/NAD+ rate was less than 1 (about 0.7), and the activities of phosphoenolpyruvate carboxylase and acetate kinase of the ldhA-deficent mutant were enhanced by 84% and 12 times, respectively. Our studies show that succinicate and acetate production pathways are strengthened by blocking lactate synthesis. It also suggests that improving NADH supply and eliminating acetate generation are alternative strategies to get high succinate-producer.

Mechanism of arginine deiminase activity by site-directed mutagenesis / 生物工程学报

Arginine deiminase (ADI) has been studied as a potential anti-cancer agent for inhibiting arginine-auxotrophic tumors (such as melanomas and hepatocellular carcinomas) in phase III clinical trials. In this work, we studied the molecular mechanism of arginine deiminase activity by site-directed mutagenesis. Three mutation sites, A128, H404 and 1410, were introduced into wild-type ADI gene by QuikChange site-directed mutagenesis method, and four ADI mutants M1 (A128T), M2 (H404R), M3 (I410L), and M4 (A128T, H404R) were obtained. The ADI mutants were individually expressed in Escherichia coli BL21 (DE3), and the enzymatic properties of the purified mutant proteins were determined. The results show that both A128T and H404R had enhanced optimum pH, higher activity and stability of ADI under physiological condition (pH 7.4), as well as reduced K(m) value. This study provides an insight into the molecular mechanism of the ADI activity, and also the experimental evidence for the rational protein evolution in the future.

Recent trend of nonaqueous enzymology and biocatalysis in nonaqueous media / 生物工程学报

With the rapid development of industrial biotechnology, breakthrough in enzymology and biocatalysis has been made in recent years, especially in areas of stability and activity of enzyme in nonaqueous media, screening, construction and modification of solvent-tolerant biocatalysts, as well as the development of green solvent with excellent biological and environmental compatibility. Recent trend and future focus include: in silico virtual screening and construction of solvent-tolerant biocatalysts based on bioinformatic technology, modification and construction of native solvent-tolerant biocatalysts, the development of environmental friendly green solvent such as ionic liquids.

Effect of Different Carbon Sources on Succinic Acid Production of Actinobacillus succinogenes and Metabolic Flux Analysis / 微生物学通报

In anaerobic bottles fermentation,glucose,fructose,xylose,lactose,maltose,sucrose and sugar alcohols could be used to produce succinic acid with Actinobacillus succinogenes. When sorbitol was utilized as the carbon source in the batch fermentation,more succinate and ethanol were produced compared with those using glucose,while producing less acetate and formate. The metabolic flux analysis results showed that the flux partitioning at PEP node was stable when glucose was replaced by sorbitol,but the flux partitioning at PYR and AcCoA nodes changed a lot because more reducing power(NADH) was generated to meet the more requirement the synthesis of succinate and ethanol.

Environmental factors affecting the succinic acid production by Actinobacillus succinogenes CGMCC 1593 / 生物工程学报

Actinobacillus succinogenes is a promising candidate for the production of bio-based succinic acid. Previously, we isolated a succinic acid-producing strain Actinobacillus succinogenes CGMCC 1593 from bovine rumen. In this paper, the influence of the environmental factors such as gas phase, pH, ORP, on succinic acid production by A. succinogenes CGMCC 1593 was studied. The results showed that CO2 was the optimum gas phase for anaerobic fermentation ofA. succinogenes CGMCC 1593 as well as one of the substrate for the succinic acid synthesis. Using MgCO3 as a pH regulator, the pH was maintained within 7.1-6.2 during the anaerobic fermentation for the cell growth and acid production of A. succinogenes CGMCC 1593. Our results showed that low initial ORP was disadvantageous for the growth of A. succinogenes CGMCC 1593 and an ORP of -270 mV was demonstrated to be beneficial to the succinic acid production. By adding Na2S.9H2O to decrease ORP to -270 mV at the end of exponential growth phase in batch culture of A. succinogenes CGMCC 1593, the succinic acid concentration reached 37 g/L and the yield of succinic acid was 129% at 48 h. This work might provide valuable information for further optimization of succinic acid fermentation by A. succinogenes CGMCC 1593.

Breeding of monofluoroacetate-resistant strains of Actinobacillus succinogenes and the mechanism based on metabolic flux analysis / 生物工程学报

Succinic acid has received a great deal of attention as an important green chemical stock for the manufacture of synthetic resins, biodegradable polymers and chemical intermediates. In this paper, the breeding mechanism of Actinobacillus succinogenes based on metabolic flux analysis was demonstrated to improve the yield of succinic acid by fermentation. After the NTG treatment, mutants from A. succinogenes CGMCC 1593 which were able to grow in medium containing concentrations of about 50-100 mmol/L of sodium monofluoroacetate were obtained. Among them, a mutant SF-9 was selected for producing more succinic acid and less acetic acid. When fermentations were conducted in a 5 L bioreactors, the final succinic acid concentration of SF-9 (34.8 g/L) increased 23.4%, and the mass ratio of succinic acid/acetic acid increased from 3.3 to 9 compared with those of the parent strain. Based on the metabolic flux analysis of A. succinogenes, PEP was found to be a key node which has an important effect on the production of succinic acid, and the flux ratio of by-productions (acetic, formic, lactic acid) was influenced by PYR node. Compared with the parent strain, the flux to succinic acid of mutant (A. succinogenes SF-9) was significantly increased, while the flux to by-productions had an obvious decline. Therefore, PEP and PYR are not rigid nodes in the metabolic regulation of A. succinogenes.