Statistical optimization of medium composition for aspergiolide A production by marine-derived fungus Aspergillus glaucus.

Statistical methodologies were employed to optimize submerged culture medium for the production of a novel antineoplastic compound aspergiolide A by a marine-derived fungus Aspergillus glaucus HB1-19 for the first time. Orthogonal design was preformed to determine the initial composition. Then Plackett-Burman design was applied to evaluate the influence of related nutrients, and yeast extract paste, soybean powder and sodium glutamate were confirmed as critical factors in the medium. Response surface methodology (RSM) was finally taken as an effective approach to optimize the combination of the obtained three significant factors. The predicted maximal aspergiolide A production of 62.4 mg/L appeared at the region where the concentrations of sodium glutamate, soybean powder, and yeast extract paste were 2, 1, and 1.07 g/L, respectively. Under the proposed optimized conditions, the experimental aspergiolide A production reached 71.2 mg/L. The correlation between predicted value and measured value of these experiments proved the validity of the response model. After optimization, aspergiolide A production increased 4.22 times compared to that of the original medium. Elemental analysis was finally taken into consideration, and carbon-nitrogen ratio in the medium increased from 20.1:1 to 86.6:1. This great difference was inferred as the most important reason for production enhancement by metabolic pathway analysis.

[Refolding of the fusion protein of recombinant enterokinase light chain rEKL].

The fusion protein of enterokinase light chain, DsbA-rEKL, was expressed mainly in inclusion body in E. coli. The recombinant bacteria was fermented to high density, with high expression of the fusion protein. After being washed with 0.5% Triton X-100 and 4mol/L urea, the inclusion body was dissolved in 6mol/L guanidine and 100mmol/L DTP, derivatized by cystine and refolded by pulse refolding. The strategy of pulse refolding involved the addition of 0.03mg/mL of fusion protein until its final concentration reached 0.3mg/mL. The refolded protein was autocleaved and the active EKL molecule was released after adding 2mmol/L CaCl2. Using the two-step purification processes of IDA-Sepharose chromatography and Q-Sepharose chromatography, the purity of rEKL was found to be above 95%, with a high activity to cleave the recombinant reteplase fusion protein Trx-rPA. The yield of purified rEKL was more than 60mg/L of cultures. As a result, the therapeutic proteins like rPA could be produced on a large-scale in a way such as expressed in the form of fusion proteins.

[Detection of intracellular reactive oxygen species by flow cytometry in Pichia pastoris fermentation].

In Pichia pastoris fermentation, methanol was oxidized into carbon oxide and produced a byproduct H2 O2, one of the partially reduced forms of molecular oxygen known as reactive oxygen species (ROS) . ROS are highly damaging towards cellular constituents. Flow cytometry (FCM) is an excellent method that permits the rapid, optical analysis of individual cells and has many advantages over conventional cytometry. However, its use in detecting intracellular ROS levels during Pichia fermentation was rarely reported. In our work, by means of flow cytometry, two fluorescent dye 2', 7'-dichlorofluorescin diacetate (DCFH-DA) and propidium iodide (PI) were used to detect ROS. The effect of intracellular ROS on Pichia pastoris cells during fermentation was studied through the comparison between DCFH-DA/PI double-stained cells and PI single-stained cells. In this study, the loss of cell viability during fermentation was correlated with the accumulation of ROS. At the glycerol batch and fed-batch phase, little ROS was accumulated intracellularly and cell viability reached almost 100%. At the early methanol fed-batch phase, intracellular ROS accumulation took place but 98.5% cells still kept viable. At the later methanol fed-batch phase, 94.0% cells accumulated high ROS. As a result, some cells lost their viability because of the damage of ROS. 25.4% dead cells accumulated high ROS in the total 29.1% dead cells.

[Metabolism of recombinant CHO-GS cell reducing of toxic effect of ammonia].

The toxic effect of ammonia on rCHO-GS cell decreased obviously due to the transfection of GS system in serum-free culture. The maximum cell density, 15.6 x 10(5) cells/mL was obtained in the culture with 1.42 mmol/L ammonia. The growth of rCHO-GS cell was inhibited with an increased ammonia concentration. However, a cell density of 8.9 x 10(5) cells/mL was obtained when the concentration of ammonia was 12.65mmol/L. The intracellar metabolic pathways were affected due to the decrease of the toxic effect of ammonia on rCHO-GS cell. With the increase of initial ammonia concentration from 0.36mmol/L to 12.65mmol/L, the yield coefficients of cell to glucose and lactate to glucose decreased. The activities of hexokinase (HK), pyruvate kinase (PK), and lactate dehydrogenase (LDH) increased by 43%, 140% and 25%, respectively, indicating that the utilization of glucose increased and the glycolysis pathway was more prone to efficient energy metabolism pathway. An increased activity of glutamate-pyruvate aminotransferase (GPT) showed that the conversation from glutamate to alpha-ketoglutarate was shifted to glutamate-pyruvate transamination pathway. The deamination pathway was inhibited due to a decreased activity of glutamate dehydrogenase. In addition, the number of cells in G0/G1 phase increased and the specific production rate of recombinant protein increased by 2.1-fold with the increase of initial ammonia concentration from 0.36mmol/L to 12.65mmol/L.

Purification and identification of recombinant hirudin and its degradation products expressed in Pichia pastoris.

The purification and identification of recombinant hirudin (r-hirudin) (rHV2-Lys47) and its several C-terminal proteolytic degradation derivatives, produced by Pichia pastoris, were described. The high-purity rHV2-Lys47 of above 99% and its three degradation products were obtained by a straightforward two-step chromatography procedure, a combination of cation exchange and reverse phase chromatography, with a recovery yield of 74% for hirudin. The purified rHV2 had the predicted N-terminal amino acid sequence and the derivatives were the degradation products of hirudin, short of one to three amino acid residues at C-terminal.

[Microbial transformation of sinenxan A, a rich constituent in callus cultures of Taxus].

AIM: To study the microbial transformation of sinenxan A. METHODS: Choose two strains of Fungi (Mucor spinosus AS 3.3450 and Cunninghamella echinulata AS 3.3400) and a strain of bacterium (Proteus vulgaris AS 1.1208) to transform the substrate. RESULTS: Three products were obtained and identified as 10-deacetylsinenxan A1, 6 alpha-hydroxy-10-deacetylsinenxan A2 and 9 alpha-hydroxy-10-deacetylsinenxan A3 respectively. CONCLUSION: Sinenxan A is facile to be transformed by microorganisms, the 10-acetyl group of which is an active group.

DNA sequencing of a plasmid with virulence from marine fish pathogen Vibrio anguillarum.

DNA sequence of a plasmid pEIB1 associated with virulence from the marine fish pathogen Vibrio anguillarum was determined using the methods of restriction endonuclease digestion, subcloning, and primer walking. The whole length of obtained pEIB1 DNA sequence was 66 164 bp, and the overall G+C content of DNA sequence is 42.7%. This sequence encodes 44 open reading frames containing the genes of DNA replication, biosynthesis and regulation of the siderophore anguibactin and transport of ferric-anguibactin complexes.

Estimation of Chinese hamster ovary cell density in packed-bed bioreactor by lactate production rate.

A method is described for estimating recombinant Chinese hamster ovary (rCHO) cell density in a packed-bed bioreactor by lactate production rate. The lactate production rate, which depended on both the cell numbers and cell growth rate, was modeled by segregating the cell population into two parts: one growing at a maximum specific growth rate and another non-growing. The individual cell in each part had the same lactate production rate. The established rate equation of lactate production matched the experimental data reasonably well and could be used to estimate the cell growth in the batch culture with microcarriers. Furthermore, in the perfusion culture of rCHO cells in a packed-bed bioreactor, the final cell density, 1.3 x 10(10) cells l(-1), estimated by lactate production rate, was comparable to the direct sample counting of 1.2 x 10(10) cells l(-1), showing that lactate production rate method would be useful in tracing the cell growth in packed-bed bioreactors.

Promoter activities in the baculovirus envelope glycoprotein gp64 gene.

Baculovirus GP64 envelope glycoprotein is a specific major component of the envelope of the budded virus and is involved in virus entry into the host cells by endocytosis. For promoter activity analysis in the baculovirus gp64 gene, two DNA fragments containing 437 and 439 bp upstream of 5' ends of the BmNPV and AcMNPV gp64 ORF were amplified by polymerase chain reaction and cloned, respectively. The sequence analysis indicated that two gp64 genes have both early (CAGT) and late (A/GTAAG) transcriptional start sites. By use of the plasmids with a reporter luciferase gene (Luc) driven by gp64 promoter to transfect insect cells, transient expression assay showed that pBmgp64Luc had high expression levels in permissive Bm-N cells and very low levels in non-permissive Sf-21 cells, while pAcgp64Luc had relatively high expression levels both in permissive Sf-21 cells and in non-permissive Bm-N cells. Furthermore, the transcription of both gp64 promoters appeared to be transactivated by 2.4-4 times in corresponding permissive cells by corresponding viral factors, separately. By inserting BmNPV homologous region-3 (hr3) into the downstream of luciferase reporter gene driven by gp64 promoter, it enhanced transcription from both gp64 promoters by 13 - 22 times in Bm-N cells and over 7000 - 14,000 times in Sf-21 cells, respectively. In the presence of BmNPV hr3, correspondingly, the viral factors transactivated the transcriptional activity from two promoters by about 73 - 78 times in corresponding permissive cells. It suggested that BmNPV hr3 plays an important role in co-activation with viral factors onto the gp64 promoter besides the functions of viral DNA origin and enhancer.

[Fermentation behaviors of recombinant Pichia pastoris under inhibited methanol concentration].

Chemostat culture was performed to characterize the growth, substrate consumption and the hirudin production, and to disclose their interrelations in the fermentation of recombinant Pichia pastoris. The Andrew substrate-inhibited growth model is more suitable than Monod model to simulate the growth of Pichia pastoris on methanol. Therefore, two stationary states can be obtained in the continuous culture at a certain dilution rate because of the substrate inhibition on cell growth. The stationary state could be obtained if only the dilution rate not more than 0.048 h(-1) in the continuous fermentation. The concentrations of cell, methanol and hirudin were constant after 50 h continuous culture with dilution rate at 0.04 h(-1). However, it could not be obtained when the dilution rate more than 0.048 h(-1) because the other stationary point at S > 0.048 h(-1) is unstable. Therefore, it was found that the cell concentration declined and the methanol concentration increased from 2.9 g/L to 18.1 g/L within 18h at dilution rate 0.06 h(-1). Thus, the fed-batch culture with a constant specific growth rate was carried out to disclose the fermentation behavior at high and constant methanol concentration in aid of a methanol sensor. The theoretical maximum specific growth rate, microm = 0.0464 h(-1), was found under critical methanol concentration, Scrit = 3.1 g/L. The growth of P. pastoris was typically methanol-limited at the methanol concentration S < Scrit. It was, however, inhibited at S > Scrit. The maximum specific Hir65 production rate qp was obtained at 0.2 mg/(g x h) when methanol concentration and mu were 0.5 g/L and 0.02 h(-1), respectively. The specific Hir65 production rate qp increased with the increase of mu and S at mu < 0.02 h(-1), and decreased at mu > 0.02 h(-1). The specific methanol consumption rate increased with the increase of S when S < 5 g/L, but decreased when S > 5 g/L. At last, the high Hir65 production rate 0.2 mg/(g x h) was obtained in the fermentation conducted under methanol-limited concentration and mu controlled at 0.5 g/L and 0.02 h(-1), respectively, while the specific methanol consumption rate is low only at 0.04 g/(g x h), showing the potential for the strategy of getting high Hir65 production rate at the low consumption of methanol.

Microbial metabolism of artemisinin by Mucor polymorphosporus and Aspergillus niger.

Artemisinin (1) was transformed by Mucor polymorphosporus and Aspergillus niger. Five products were identified as 9beta-hydroxyartemisinin (2), 3beta-hydroxyartemisinin (3), deoxyartemisinin (4), 3beta-hydroxydeoxyartemisinin (5), and 1alpha-hydroxydeoxyartemisinin (6). Products 2, 3, and 6 are new compounds.

[Effects of different methanol feeding strategy on hirudin production in high-density fermentation by recombinant Pichia pastoris].

Four different methanol feeding modes were evaluated in the hirudin production in high-density fermentation by Pichia pastoris. It was difficult to avoid methanol excessive in the broth with the feeding strategy only based on DO level. On the other hand, the fluctuation in methanol concentration was observed with methanol feeding strategy by off-line gas chromatography. However, the stable methanol concentration was perfectly achieved by the on-line monitoring with methanol sensor. The supply of energy was improved by feeding glycerol at a limited rate as well as methanol in the induction phase. Therefore, the high cell dry weight (162 g/L) and high hirudin activity (2.4 x 10(4) ATU/mL or 1.7 g/L) was obtained in the fed-batch fermentation of recombinant Pichia pastoris by methanol-glycerol mixed feeding.