Jianmin Xing

Biodesulfurization of Dibenzothiophene by Microbial Cells Coated with Magnetite Nanoparticles

ABSTRACT Microbial cells of Pseudomonas delafieldii were coated with magnetic Fe3O4 nanoparticles and then immobilized by external application of a magnetic field. Magnetic Fe3O4 nanoparticles were synthesized by a coprecipitation method followed by modification with ammonium oleate. The surface-modified Fe3O4 nanoparticles were monodispersed in an aqueous solution and did not precipitate in over 18 months. Using transmission electron microscopy (TEM), the average size of the magnetic particles was found to be in the range from 10 to 15 nm. TEM cross section analysis of the cells showed further that the Fe3O4 nanoparticles were for the most part strongly absorbed by the surfaces of the cells and coated the cells. The coated cells had distinct superparamagnetic properties. The magnetization (δs) was 8.39 emu · g−1. The coated cells not only had the same desulfurizing activity as free cells but could also be reused more than five times. Compared to cells immobilized on Celite, the cells coated with Fe3O4 nanoparticles had greater desulfurizing activity and operational stability.

In situ magnetic separation and immobilization of dibenzothiophene-desulfurizing bacteria

In situ cell separation and immobilization of bacterial cells for biodesulfurization were developed by using superparamagnetic Fe(3)O(4) nanoparticles (NPs). The Fe(3)O(4) NPs were synthesized by coprecipitation followed by modification with ammonium oleate. The surface-modified NPs were monodispersed and the particle size was about 13 nm with 50.8 emu/g saturation magnetization. After adding the magnetic fluids to the culture broth, Rhodococcus erythropolis LSSE8-1 cells were immobilized by adsorption and then separated with an externally magnetic field. The maximum amount of cell mass adsorbed was about 530 g dry cell weight/g particles to LSSE8-1 cells. Analysis showed that the nanoparticles were strongly absorbed to the surface and coated the cells. Compared to free cells, the coated cells not only had the same desulfurizing activity but could also be easily separated from fermentation broth by magnetic force. Based on the adsorption isotherms and Zeta potential analysis, it was believed that oleate-modified Fe(3)O(4) NPs adsorbed bacterial cells mainly because of the nano-size effect and hydrophobic interaction.

Efficient conversion of crop stalk wastes into succinic acid production by Actinobacillus succinogenes

Succinic acid is valued as a key platform chemical for use in a variety of synthetic applications. Efficient biosynthesis of succinic acid from renewable biomass resource is reported in this paper. Batch fermentations were carried out to analyze influence of several carbon sources on succinic acid production from feedstock wastes by Actinobacillus succinogenes BE-1. Crop stalk wastes, including corn stalk and cotton stalk, were enzymatically converted into a carbohydrate-rich feedstock, obtaining glucose concentrations approaching 65-80% of the total reducing sugar. For the anaerobic batch cultivation with cotton stalk hydrolysates, the production of succinic acid was 15.8 g l(-1) with a high yield of 1.23 g per g glucose. Glucose and xylose were utilized at same time, while cellubiose was not consumed until glucose and xylose were completely consumed.

Construction of reductive pathway in Saccharomyces cerevisiae for effective succinic acid fermentation at low pH value.

Succinic acid is an important precursor for the synthesis of high-value-added products. Saccharomyces cerevisiae is a suitable platform for succinic acid production because of its high tolerance towards acidity. In this study, a modified pathway for succinate production was established and investigated in S. cerevisiae. The engineered strain could produce up to 6.17±0.34g/L of succinate through the constructed pathway. The succinate titer was further improved to 8.09±0.28g/L by the deletion of GPD1 and even higher to 9.98±0.23g/L with a yield of 0.32mol/mol glucose through regulation of biotin and urea levels. Under optimal supplemental CO2 conditions in a bioreactor, the engineered strain produced 12.97±0.42g/L succinate with a yield of 0.21mol/mol glucose at pH 3.8. These results demonstrated that the proposed engineering strategy was efficient for succinic acid production at low pH value.

Membrane fouling mechanism in ultrafiltration of succinic acid fermentation broth

The membrane fouling mechanism was studied in treating succinic acid fermentation broth during dead-end ultrafiltration. Different membranes were used and two models were applied to analyze the fouling mechanism. Resistance-in-series model was applied to determine the main factor that caused the operation resistance. Results indicated that most membranes tended to be fouled by cake layer or concentration polarization. Hermias model, which is composed of four individual sub-models, was used to analyze the predominant fouling mechanism. Results showed that the fouling of RC 10 kDa and PES 30 kDa was controlled by the complete blocking mechanism, while PES 100 kDa was controlled by the intermediate blocking and PES 10 kDa was controlled by cake layer. This conclusion was also proved by SEM photos. Membrane characteristics were monitored before and after ultrafiltration by AFM and goniometer. Both contact angle and roughness of most membranes increased after ultrafiltration.

Desulfurization of Diesel Fuel by Extraction with Lewis-Acidic Ionic Liquid

Abstract Ionic liquids were found to be highly selective for the extractive removal of aromatic sulfur compounds from fuels at room temperature. The efficiency of ionic liquids for the removal of aromatic sulfur compounds is dependent on the properties and structure of the ionic liquids. In this work, the Lewis-acidic ionic liquid 1-butyl-3-methylimidazolium tetrahalogenoferrate(III) ([BMIM] [FeCl4]) was synthesized and demonstrated to be more effective for the removal of aromatic sulfur compounds from diesel over ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM] [BF4]) because of its Lewis-acidic property. The ionic liquids favorably extracted organic compounds with a higher density of aromatic π-electrons. [BMIM][FeCl4] ionic liquid can be regenerated through reextraction by hexane, and could be used in multiple steps for the removal of sulfur compounds from diesel.

SiRNA-phospholipid conjugates for gene and drug delivery in cancer treatment

Due to low charge density and stiff backbone structure, small interfering RNA (siRNA) has inherently poor binding ability to cationic polymers and lipid carriers, which results in low siRNA loading efficiency and limits siRNA success in clinical application. Here, siRNA-phospholipids conjugates are developed, which integrate the characteristics of the two phospholipids to self-assemble via hydrophilic siRNA and hydrophobic phospholipid tails to overcome the siRNAs stiff backbone structures and enhance the siRNA loading efficiency. In this study, the thiol-modified sense and antisense siRNA are chemically conjugated with phospholipids to form sense and antisense siRNA-phospholipid, and then these sense or antisense siRNA-phospholipids with equal amounts are annealed to generate siRNA-phospholipids. The siRNA-phospholipids can serve dual functions as agents that can silence gene expression and as a component of nanoparticles to embed hydrophobic anticancer drugs to cure tumor. siRNA-phospholipids together with cationic lipids and DSPE-PEG2000 fuse around PLGA to form siRNA-phospholipids enveloped nanoparticles (siRNA-PCNPs), which can deliver siRNAs and hydrophobic anticancer drugs into tumor. In animal models, intravenously injected siRNA-PCNPs embedded DOX (siPlk1-PCNPs/DOX) is highly effective in inhibiting tumor growth. The results indicate that the siRNA-PCNPs can be potentially applied as a safe and efficient gene and anticancer drug delivery carrier.

Kinetic evaluation of products inhibition to succinic acid producers Escherichia coli NZN111, AFP111, BL21, and Actinobacillus succinogenes 130Z(T)

Succinic acid is one of the platform compounds and its production via natural feedstocks has drawn worldwide concerns. To evaluate the inhibitory effects of fermentation products on the growth of Actinobacillus succinogenes 130ZT and Escherichia coli NZN111, AFP111, BL21, fermentations with addition of individual products in medium were carried out. The cell growth was inhibited when the concentrations of formate, acetate, lactate, and succinate were at range of 8.8–17.6 g/L, 10–40 g/L, 9–18 g/L, and 10–80 g/L, respectively. For these two species of bacteria, E. coli was more resistant to acid products than A. succinogenes, while both endured succinate rather than by-products. As a result of end product inhibition, succinate production yield by A. succinogenes decreased from 1.11 to 0.49 g/g glucose. Logistic and Monod mathematical models were presented to simulate the inhibition kinetics. The Logistic model was found more suitable for describing the overall synergistic inhibitory effects.

Novel membrane-based biotechnological alternative process for succinic acid production and chemical synthesis of bio-based poly (butylene succinate)

Succinic acid was produced in a novel membrane-based fermentation and separation integrated system. With this integrated system, product inhibition was alleviated by removing acids and replenishing fresh broth. High cell density maintain for a longer time from 75 to 130h and succinic acid concentration increased from 53 to 73g/L. In the developed separation process, succinic acid was crystallized at a recovery of 85-90%. The purity of the obtained succinic acid crystals reached 99.4% as found by HPLC and (1)H NMR analysis. A crystallization experiment indicated that among by-products glucose had a negative effect on succinic acid crystallization. Poly (butylene succinate) (PBS) was synthesized using the purified succinic acid and (1)H NMR analysis confirmed that the composition of the synthesized PBS is in agreement with that from petro-based succinic acid.

Preparation and characterization of superparamagnetic functional polymeric microparticles

Abstract Superparamagnetic poly(styrene-divinylbenzene-glycidyl methacrylate) (Pst-DVB-GMA) microparticles were prepared via a modified suspension polymerization process. A magnetic fluid was first prepared by a chemical co-precipitation method. Then magnetic microparticles were produced by mixing the monomers and the magnetic fluid with water in the presence of a stabilizer poly(vinyl pyrrolidone) (PVP) to form a suspension, and finally benzoyl peroxide was added to initiate the co-polymerization. The morphology and magnetic properties of the microparticles were examined by TEM and VSM. The spherically shaped microparticles, with a size range of 4 to 7 μm, showed distinct superparamagnetic characteristics. XRD was used to investigate the structure of the magnetite particles dispersed in the polymer matrix. The microparticles with epoxy groups on their surface can be applied directly to the separation of biomolecules.