Regulating the structure of bacterial cellulose by altering the expression of bcsD using CRISPR/dCas9 / 生物工程学报

Gluconacetobacter xylinus is a primary strain producing bacterial cellulose (BC). In G. xylinus, BcsD is a subunit of cellulose synthase and is participated in the assembly process of BC. A series of G. xylinus with different expression levels of the bcsD gene were obtained by using the CRISPR/dCas9 technique. Analysis of the structural characteristics of BC showed that the crystallinity and porosity of BC changed with the expression of bcsD. The porosity varied from 59.95%-84.05%, and the crystallinity varied from 74.26%-93.75%, while the yield of BC did not decrease significantly upon changing the expression levels of bcsD. The results showed that the porosity of bacterial cellulose significantly increased, while the crystallinity was positively correlated with the expression of bcsD, when the expression level of bcsD was below 55.34%. By altering the expression level of the bcsD gene, obtaining BC with different structures but stable yield through a one-step fermentation of G. xylinus was achieved.

Construction and optimization of Escherichia coli for producing rhamnolipid biosurfactant / 生物工程学报

Rhamnolipid biosurfactant is mainly produced by Pseudomonas aeruginosa that is the opportunistic pathogenic strain and not suitable for future industrial development. In order to develop a relatively safe microbial strain for the production of rhamnolipid biosurfactant, we constructed engineered Escherichia coli strains for rhamnolipid production by expressing different copy numbers of rhamnosyltransferase (rhlAB) gene with the constitutive synthetic promoters of different strengths in E. coli ATCC 8739. We further studied the combinatorial regulation of rhlAB gene and rhaBDAC gene cluster for dTDP-1-rhamnose biosynthesis with different synthetic promoters, and obtained the best engineered strain-E. coli TIB-RAB226. Through the optimization of culture temperature, the titer of rhamnolipd reached 124.3 mg/L, 1.17 fold higher than that under the original condition. Fed-batch fermentation further improved the production of rhamnolipid and the titer reached the highest 209.2 mg/L within 12 h. High performance liquid chromatography-mass spectrometry (LC-MS) analysis showed that there are total 5 mono-rhamnolipid congeners with different nuclear mass ratio and relative abundance. This study laid foundation for heterologous biosynthesis of rhanomilipd.

Effects of carbon and nitrogen sources on 5-keto-gluconic acid production / 生物工程学报

Gluconobacter oxydans is known to oxidize glucose to gluconic acid (GA), and subsequently, to 2-keto-gluconic acid (2KGA) and 5-keto-gluconic acid (5KGA), while 5KGA can be converted to L-(+)-tartaric acid. In order to increase the production of 5KGA, Gluconobacter oxydans HGI-1 that converts GA to 5KGA exclusively was chosen in this study, and effects of carbon sources (lactose, maltose, sucrose, amylum and glucose) and nitrogen sources (yeast extract, fish meal, corn steep liquor, soybean meal and cotton-seed meal) on 5KGA production were investigated. Results of experiment in 500 mL shake-flask show that the highest yield of 5KGA (98.20 g/L) was obtained using 100 g/L glucose as carbon source. 5KGA reached 100.20 g/L, 109.10 g/L, 99.83 g/L with yeast extract, fish meal and corn steep liquor as nitrogen source respectively, among which the optimal nitrogen source was fish meal. The yield of 5KGA by corn steep liquor is slightly lower than that by yeast extract. For the economic reason, corn steep liquor was selected as nitrogen source and scaled up to 5 L stirred-tank fermentor, and the final concentration of 5KGA reached 93.80 g/L, with its maximum volumetric productivity of 3.48 g/(L x h) and average volumetric productivity of 1.56 g/(L x h). The result obtained in this study showed that carbon and nitrogen sourses for large-scale production of 5KGA by Gluconobacter oxydans HGI-1 were glucose and corn steep liquor, respectively, and the available glucose almost completely (85.93%) into 5KGA.

Research on medical application of bacterial cellulose as nano-biomaterials / 生物医学工程学杂志

Bacterial cellulose (BC) is a high-purity nanometer cellulose secreted by some bacteria. Compared with plant cellulose, it possesses an array of unique properties, including high crystallinity, high water content, good bio-compatibility, high mechanical strength and an ultra-fine fiber network. BC is prosperous as a new type of biomedical material, which has medical applications such as wound dressing, artificial skin, artificial blood vessels and tissue engineering scaffolds. There are, however, some problems to be solved on the large-scale application of BC, such as the high cost, low yield, and poor mechanical stability and so on.

Improving 3-dehydroshikimate production by metabolically engineered Escherichia coli / 生物工程学报

In the aromatic amino acid biosynthetic pathway 3-dehydroshikimate (DHS) is a key intermediate. As a potent antioxidant and important feedstock for producing a variety of important industrial chemicals, such as adipate and vanillin, DHS is of great commercial value. Here, in this study, we investigated the effect of the co-expression of aroFFBR (3-deoxy-D-arabino-heptulosonate 7-phosphate synthase mutant with tyrosine feedback-inhibition resistance) and tktA (Transketolase A) at different copy number on the production of DHS. The increased copy number of aroFFBR and tktA would enhance the production of DHS by the fold of 2.93. In order to further improve the production of DHS, we disrupted the key genes in by-product pathways of the parent strain Escherichia coli AB2834. The triple knockout strain of ldhA, ackA-pta and adhE would further increase the production of DHS. The titer of DHS in shake flask reached 1.83 g/L, 5.7-fold higher than that of the parent strain E. coli AB2834. In 5-L fed-batch fermentation, the metabolically engineered strain produced 25.48 g/L DHS after 62 h. Metabolically engineered E. coli has the potential to further improve the production of DHS.

Cloning and characterization of a novel carbonyl reductase for asymmetric reduction of bulky diaryl ketones / 生物工程学报

Asymmetric reduction of bulky diaryl ketones is still one of the challenging tasks in biocatalysis. By genomic data mining, a putative carbonyl reductase gene pascr was found in Pichia pastoris GS115. pascr was cloned and over-expressed in Escherichia coli Rosseta2 (DE3). The recombinant enzyme was purified to homogeneity by Ni-NTA column and its catalytic properties were studied. PasCR strictly used NADPH as cofactor, gel filtration and SDS-PAGE analysis suggested that the native form of PasCR was a dimmer. PasCR exhibited the highest activity at 35 degrees C in phosphate buffer at pH 6.5. The enzyme catalyzed the reduction of some bulky diaryl ketones, such as 4-methylbenzophenone, 2-methylbenzophenone and 4-chlorobenzophenone, especially for 4-methylbenzophenone, the product S--alcohol was obtained with 85% ee.

Expression of virus-like particles of enterovirus 71 in Hansenula polymorpha / 中华微生物学和免疫学杂志

Objective To express virus-like particles(VLP) of enterovirus 71 (EV71) in Han-senula polymorpha.Methods The coding sequences of P1 and 3CD genes of EV71 were optimized accord-ing to codon usage bias of Hansenula polymorpha for achieving high expression , and then cloned into the ex-pression vector PMV of Hansenula polymorpha .The recombinant expression vector PMV-P1-3CD was trans-formed into Hansenula polymorpha AU 0501 .The transformants were stably cultured in selective medium (Yeast Nitrogen Base) and screened for strains with positive P1 and 3CD genes by PCR.Then an induced cultivation on the recombinant strains were performed in a medium supplemented with methanol to a final concentration of 1.0%and the expressed products were analyzed by SDS-PAGE and Western blot assays to select high expression strains .The high expression strains were cultured in 30 L fermentor and its fermenta-tion products were analyzed by electronic microscope after purification .Results EV71 recombinant expres-sion strains were successfully constructed .The results of SDS-PAGE showed that the expressed products had obvious VP3, VP1, VP0 protein bands with molecular weights of 26×103, 33×103 and 35×103, respective-ly, which were consistent with the expected molecular weight of the fusion proteins .Western blot demonstra-ted that the expressed products could be specifically recognized by the polyclonal antibody against EV 71-VP1 at 33 ×10 3 , indicating its high immunoreactivity .ELISA confirmed that the expression level of EV 71 fermen-tation products was reached to 200 mg/L.Electronic microscope analysis showed that the VLP of recombi-nant EV71 were 24-30 nm in diameter with normal structure .Conclusion The virus-like particles of human enterovirus 71 are successfully expressed in Hansenula polymorpha , which provides a foundation for the fur-ther development of EV 71 VLP vaccine .

Construction and structural analysis of integrated cellular network of Corynebacterium glutamicum / 生物工程学报

Corynebacterium glutamicum is one of the most important traditional industrial microorganisms and receiving more and more attention towards a novel cellular factory due to the recently rapid development in genomics and genetic operation toolboxes for Corynebacterium. However, compared to other model organisms such as Escherichia coli, there were few studies on its metabolic regulation, especially a genome-scale integrated cellular network model currently missing for Corynebacterium, which hindered the systematic study of Corynebacterium glutamicum and large-scale rational design and optimization for strains. Here, by gathering relevant information from a number of public databases, we successfully constructed an integrated cellular network, which was composed of 1384 reactions, 1276 metabolites, 88 transcriptional factors and 999 pairs of transcriptional regulatory relationships. The transcriptional regulatory sub-network could be arranged into five layers and the metabolic sub-network presented a clear bow-tie structure. We proposed a new method to extract complex metabolic and regulatory sub-network for product-orientated study taking lysine biosynthesis as an example. The metabolic and regulatory sub-network extracted by our method was more close to the real functional network than the simplex biochemical pathways. The results would be greatly helpful for understanding the high-yielding biomechanism for amino acids and the re-design of the industrial strains.

Docking analysis and multidimensional hybrid qsar model of l,4-benzodiazepine-2,5-Diones as HDM2 antagonists

The inhibitors of p53-HDM2 interaction are attractive molecules for the treatment of wild-type p53 tumors. In order to search more potent HDM2 inhibitors, docking operation with CDOCKER protocol in Discovery Studio 2.1 [DS2.1] and multidimensional hybrid quantitative structure-activity relationship [QSAR] studies through the physiochemical properties obtained from DS2.1 and E-Dragon 1.0 as descriptors, have been performed on 59 1, 4-benzodiazepine-2, 5-diones which have p53-HDM2 interaction inhibitory activities. The docking results indicate that n-n interaction between the imidazole group in HIS96 and the aryl ring at 4-N of l, 4-benzodiazepine-2, 5-dione may be one of the key factors for the combination of ligands with HDM2. Two QSAR models were obtained using genetic function approximation [GFA] and genetic partial least squares [G/PLS] based on the descriptors obtained from DS2.1 and E-dragon 1.0, respectively. The best model can explain 85.5% of the variance [R[2][cv] while it could predict 81.7% of the variance [R[2]CV] With this model, the bioactivities of some new compounds were predicted

Purification and characterization of extracellular polysaccharides from Nostoc flagelliforme / 生物工程学报

The extracellular polysaccharides (EPS) of N. flagelliforme were purified by DEAE anion exchange chromatography and Sephadex G100 gel filtration chromatography. And two main components named NFPS1 and NFPS2 were obtained respectively. The physico-chemical characteristics of NFPS2 were analyzed and compared with NFPS0, which was obtained from field colony of N. flagelliforme. These results showed that both of NFPS2 and NFPSO were composed of four monosaccharides: glucose, xylose, galactose and mannose. The apparent molecular weight of NFPS2 and NFPS0 was estimated to be 2.79 x 10(5), 2.26 x 10(5) respectively. They are non-sulfated polysaccharides, free of protein and nuclear acid. The thermal analysis indicated that there was a decomposition peak at 245 degrees C in thermogravimetric (TG) curves. However, the microstructure analysis showed that they had different porous structures.