Production of MBP–HepA fusion protein in recombinant Escherichia coli by optimization of culture medium

Combination of engineering the substrate and Ca2+ binding domains of heparinase I to improve the catalytic activity

Heparinase I (EC 4.2.2.7), is an enzyme that cleaves heparin, showing great potential for eco-friendly production of low molecular weight heparin (LMWH). However, owing to its poor catalytic activity and thermal stability, the industrial application of heparinase I has been severely hindered. To improve the catalytic activity, we proposed to engineer both the substrate and Ca2+ binding domains of heparinase I. Several heparinases I from different organisms were selected for multiple sequence alignment and molecular docking to screen the key residues in the binding domain. Nine single-point mutations were selected to enhance the catalytic activity of heparinase I. Among them, T250D was the most highly active one, whereas mutations around Ca2+ binding domain yielded two active mutants. Mutant D152S/R244K/T250D with significantly increased catalytic activity was obtained by combined mutation. The catalytic efficiency of the mutant was 118,875.8 min-1·µM-1, which was improved 5.26 times. Molecular modeling revealed that the improved activity and stability of the mutants were probably attributed to the formation of new hydrogen bonds. The highly active mutant had great potential applications in industry and the strategy could be used to improve the performance of other enzymes.

Cloning, Expression, and Characterization of a Highly Stable Heparinase I from Bacteroides xylanisolvens

Heparinase I (Hep I), which specifically degrades heparin to oligosaccharide or unsaturated disaccharide, has an important role in the production of low molecular weight heparin (LMWH). However, low productivity and stability of heparinase I hinders its applications. Here, a novel heparinase I (BxHep-I) was cloned from Bacteroides xylanisolvens and overexpressed in soluble form in Escherichia coli. The expression conditions of BxHep-I were optimized for an activity of 7144 U/L. BxHep-I had a specific activity of 57.6 U/mg at the optimal temperature and pH of 30 °C and pH 7.5, with the Km and Vmax of 0.79 mg/mL and 124.58 U/mg, respectively. BxHep-I catalytic activity could be enhanced by Ca2+ and Mg2+, while strongly inhibited by Zn2+ and Co2+. Purified BxHep-I displayed an outstanding thermostability with half-lives of 597 and 158 min at 30 and 37 °C, respectively, which are the highest half-lives ever reported for heparinases I. After storage at 4 °C for one week, BxHep-I retained 73% of its initial activity. Molecular docking revealed that the amino acids Asn25, Gln27, Arg88, Lys116, His156, Arg161, Gln228, Tyr356, Lys358, and Tyr362 form 13 hydrogen bonds with the substrate heparin disaccharides in the substrate binding domain and are mainly involved in the substrate binding of BxHep-I. These results suggest that the BxHep-I with high stability could be a candidate catalyst for the industrial production of LMWH.

Production of l-Methionine from 3-Methylthiopropionaldehyde and O-Acetylhomoserine by Catalysis of the Yeast O-Acetylhomoserine Sulfhydrylase

l-Methionine is an essential bioactive amino acid with high commercial value for diverse applications. Sustained attentions have been paid to efficient and economical preparation of l-methionine. In this work, a novel method for l-methionine production was established using O-acetyl-homoserine (OAH) and 3-methylthiopropionaldehyde (MMP) as substrates by catalysis of the yeast OAH sulfhydrylase MET17. The OAH sulfhydrylase gene Met17 was cloned from Saccharomyces cerevisiae S288c and overexpressed in Escherichia coli BL21. A 49 kDa MET17 was detected in the supernatant of the recombinant E. coli strain BL21-Met17 lysate with IPTG induction, which exhibited the biological activity of l-methionine biosynthesis from OAH and MMP. The recombinant MET17 was then purified from E. coli BL21-Met17 and used for in vitro biosynthesis of l-methionine. The maximal conversion rate (86%) of OAH to l-methionine catalyzed by purified MET17 was achieved by optimization of the molar ratio of OAH to MMP. The method proposed in this study provides a possible novel route for the industrial production of l-methionine.

Production of Methionol from 3-Methylthiopropionaldehyde by Catalysis of the Yeast Alcohol Dehydrogenase Adh4p

Methionol is a sulfur-containing aroma compound that contributes to the flavors of fermented foods. In this work, a novel method for methionol production was established using 3-methylthiopropionaldehyde (MMP) and alcohol dehydrogenase (ADH). First, expression of seven ADH genes was analyzed in yeast fermentation added with MMP. Only ADH4 displayed an evident increased expression in response to MMP. ADH4 was then overexpressed in Saccharomyces cerevisiae S288c and Escherichia coli BL21. The recombinant yeast strain S4 produced more methionol than control strain in MMP fermentation. Furthermore, 0.55 g/L 42 kDa Adh4p was prepared from E. coli by induced expression and purification. A fed-batch catalysis system was finally established to produce methionol from MMP by Adh4p. In 10 h of continuous catalysis, the conversion rate of MMP remained 80-95%, and a final yield of 0.2 g/L methionol was achieved. This work proposed a novel method for methionol production by enzymatic catalysis with a potential application prospect in industry.

Structure-based engineering of heparinase I with improved specific activity for degrading heparin

BACKGROUND

Heparinase I from Pedobacter heparinus (Ph-HepI), which specifically cleaves heparin and heparan sulfate, is one of the most extensively studied glycosaminoglycan lyases. Enzymatic degradation of heparin by heparin lyases not only largely facilitates heparin structural analysis but also showed great potential to produce low-molecular-weight heparin (LMWH) in an environmentally friendly way. However, industrial applications of Ph-HepI have been limited by their poor yield and enzyme activity. In this work, we improve the specific enzyme activity of Ph-HepI based on homology modeling, multiple sequence alignment, molecular docking and site-directed mutagenesis.

RESULTS

Three mutations (S169D, A259D, S169D/A259D) exhibited a 50.18, 40.43, and 122.05% increase in the specific enzyme activity and a 91.67, 108.33, and 75% increase in the yield, respectively. The catalytic efficiencies (k_cat/K_m) of the mutanted enzymes S169D, A259D, and S169D/A259D were higher than those of the wild-type enzyme by 275, 164, and 406%, respectively. Mass spectrometry and activity detection showed the enzyme degradation products were in line with the standards of the European Pharmacopoeia. Protein structure analysis showed that hydrogen bonds and ionic bonds were important factors for improving specific enzyme activity and yield.

CONCLUSIONS

We found that the mutant S169D/A259D had more industrial application value than the wild-type enzyme due to molecular modifications. Our results provide a new strategy to increase the catalytic efficiency of other heparinases.

The Goldilocks Approach: A Review of Employing Design of Experiments in Prokaryotic Recombinant Protein Production

The production of high yields of soluble recombinant protein is one of the main objectives of protein biotechnology. Several factors, such as expression system, vector, host, media composition and induction conditions can influence recombinant protein yield. Identifying the most important factors for optimum protein expression may involve significant investment of time and considerable cost. To address this problem, statistical models such as Design of Experiments (DoE) have been used to optimise recombinant protein production. This review examines the application of DoE in the production of recombinant proteins in prokaryotic expression systems with specific emphasis on media composition and culture conditions. The review examines the most commonly used DoE screening and optimisation designs. It provides examples of DoE applied to optimisation of media and culture conditions.

Novel Method for l-Methionine Production Catalyzed by the Aminotransferase ARO8 from Saccharomyces cerevisiae

The aminotransferase ARO8 was proved to play an efficient role in conversion of l-methionine into methionol via the Ehrlich pathway in Saccharomyces cerevisiae in our previous work. In this work, the reversible transamination activity of ARO8 for conversion of α-keto-γ-(methylthio) butyric acid (KMBA) into l-methionine was confirmed in vitro. ARO8 was cloned from S. cerevisiae S288c and overexpressed in Escherichia coli BL21. A 2-fold higher aminotransferase activity was detected in the recombinant strain ARO8-BL21, and ARO8 was detected in the supernatant of ARO8-BL21 lysate with IPTG induction by SDS-PAGE analysis. The recombinant ARO8 was then purified and used for transforming KMBA into l-methionine. An approximately 100% conversion rate of KMBA into l-methionine was achieved by optimized enzymatic reaction catalyzed by ARO8. This work fulfilled l-methionine biosynthesis catalyzed by the aminotransferase ARO8 using glutamate and KMBA, which provided a novel method for l-methionine production by enzymatic catalysis with the potential application prospect in industry.

Enhanced Production of Crude Violacein from Glucose in Escherichia coli by Overexpression of Rate-Limiting Key Enzyme(S) Involved in Violacein Biosynthesis

Crude violacein, consisting of violacein and deoxyviolacein, displays many attractive bio-activities in the field of drug therapy. To produce crude violacein from an industrially economic carbon source, we firstly introduced the violacein pathway into Escherichia coli B8/pTRPH1, which was previously engineered to accumulate tryptophan from glucose. A crude violacein production capacity of 0.25 g L^-1 OD₆₀₀^-1 was obtained using glucose-containing medium. By further overexpressing each of the five genes involved in violacein synthesis pathway, VioE was found as the rate-limiting step for the violacein production. The optimal strain of B8/pTRPH1-pVio-VioE was then used for fed-batch fermentation in a 5-L bioreactor and a crude violacein titer of 4.45 g L^-1, as well as a productivity of 98.7 mg L^-1 h^-1, was obtained. This engineered strain showed the highest violacein titer and productivity reported so far. Our optimal strain of E. coli B8/pTRPH1-pVio-VioE by overexpression of the rate-limiting VioE in violacein synthesis pathway was a potential violacein producer by directly using glucose for industrial application.

Establishment of chondroitin B lyase-based analytical methods for sensitive and quantitative detection of dermatan sulfate in heparin

Dermatan sulfate (DS) is one of the hardest impurities to remove from heparin products due to their high structural similarity. The development of a sensitive and feasible method for quantitative detection of DS in heparin is essential to ensure the clinical safety of heparin pharmaceuticals. In the current study, based on the substrate specificity of chondroitin B lyase, ultraviolet spectrophotometric and strong anion-exchange high-performance liquid chromatographic methods were established for detection of DS in heparin. The former method facilitated analysis in heparin with DS concentrations greater than 0.1mgmL(-1) at 232nm, with good linearity, precision and recovery. The latter method allowed sensitive and accurate detection of DS at concentrations lower than 0.1mgmL(-1), exhibiting good linearity, precision and recovery. The linear range of DS detection using the latter method was between 0.01 and 0.5mgmL(-1).

Simple procedure applying lactose induction and one-step purification for high-yield production of rhCIFN

Recombinant consensus interferon (CIFN) is a therapeutic protein with molecular weight of 19.5 kDa having broad spectrum antiviral activity. Recombinant human CIFN (rhCIFN) has previously been expressed in Escherichia coli using isopropyl-β-d-thiogalactopyranoside (IPTG), a non-metabolizable and expensive compound, as inducer. For economical and commercial-scale recombinant protein production, it is greatly needed to increase the product yield in a limited time frame to reduce the processing cost. To reduce the cost of production of rhCIFN in E. coli, induction was accomplished by using lactose instead of IPTG. Lactose induction (14 g/L) in shake flask experiment resulted in higher yield as compared with 1 mM IPTG. Finally, with single-step purification on DEAE sepharose, 150 mg/L of >98% pure rhCIFN was achieved. In the present study, an attempt was made to develop a low cost process for producing quality product with high purity. Methods devised may be helpful for pilot-scale production of recombinant proteins at low cost.

High crude violacein production from glucose by Escherichia coli engineered with interactive control of tryptophan pathway and violacein biosynthetic pathway

Background

As bacteria-originated crude violacein, a natural indolocarbazole product, consists of violacein and deoxyviolacein, and can potentially be a new type of natural antibiotics, the reconstruction of an effective metabolic pathway for crude violacein (violacein and deoxyviolacein mixture) synthesis directly from glucose in Escherichia coli was of importance for developing industrial production process.

Results

Strains with a multivariate module for varied tryptophan productivities were firstly generated by combinatorial knockout of trpR/tnaA/pheA genes and overexpression of two key genes trpE^fbr/trpD from the upstream tryptophan metabolic pathway. Then, the gene cluster of violacein biosynthetic pathway was introduced downstream of the generated tryptophan pathway. After combination of these two pathways, maximum crude violacein production directly from glucose by E. coli B2/pED + pVio was realized with a titer of 0.6 ± 0.01 g L⁻¹ in flask culture, which was four fold higher than that of the control without the tryptophan pathway up-regulation. In a 5-L bioreactor batch fermentation with glucose as the carbon source, the recombinant E. coli B2/pED + pVio exhibited a crude violacein titer of 1.75 g L⁻¹ and a productivity of 36 mg L⁻¹ h⁻¹, which was the highest titer and productivity reported so far under the similar culture conditions without tryptophan addition.

Conclusion

Metabolic pathway analysis using ¹³C labeling illustrated that the up-regulated tryptophan supply enhanced tryptophan metabolism from glucose, whereas the introduction of violacein pathway drew more carbon flux from glucose to tryptophan, thereby contributing to the effective production of crude violacein in the engineered E. coli cell factory.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0192-x) contains supplementary material, which is available to authorized users.

Phenotyping the quality of complex medium components by simple online-monitored shake flask experiments

Background

Media containing yeast extracts and other complex raw materials are widely used for the cultivation of microorganisms. However, variations in the specific nutrient composition can occur, due to differences in the complex raw material ingredients and in the production of these components. These lot-to-lot variations can affect growth rate, product yield and product quality in laboratory investigations and biopharmaceutical production processes. In the FDA’s Process Analytical Technology (PAT) initiative, the control and assessment of the quality of critical raw materials is one key aspect to maintain product quality and consistency. In this study, the Respiration Activity Monitoring System (RAMOS) was used to evaluate the impact of different yeast extracts and commercial complex auto-induction medium lots on metabolic activity and product yield of four recombinant Escherichia coli variants encoding different enzymes.

Results

Under non-induced conditions, the oxygen transfer rate (OTR) of E. coli was not affected by a variation of the supplemented yeast extract lot. The comparison of E. coli cultivations under induced conditions exhibited tremendous differences in OTR profiles and volumetric activity for all investigated yeast extract lots of different suppliers as well as lots of the same supplier independent of the E. coli variant. Cultivation in the commercial auto-induction medium lots revealed the same reproducible variations. In cultivations with parallel offline analysis, the highest volumetric activity was found at different cultivation times. Only by online monitoring of the cultures, a distinct cultivation phase (e.g. glycerol depletion) could be detected and chosen for comparable and reproducible offline analysis of the yield of functional product.

Conclusions

This work proves that cultivations conducted in complex media may be prone to significant variation in final product quality and quantity if the quality of the raw material for medium preparation is not thoroughly checked. In this study, the RAMOS technique enabled a reliable and reproducible screening and phenotyping of complex raw material lots by online measurement of the respiration activity. Consequently, complex raw material lots can efficiently be assessed if the distinct effects on culture behavior and final product quality and quantity are visualized.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-014-0149-5) contains supplementary material, which is available to authorized users.

Experimental design approach in recombinant protein expression: determining medium composition and induction conditions for expression of pneumolysin from Streptococcus pneumoniae in Escherichia coli and preliminary purification process

Background

Streptococcus pneumoniae (S. pneumoniae) causes several serious diseases including pneumonia, septicemia and meningitis. The World Health Organization estimates that streptococcal pneumonia is the cause of approximately 1.9 million deaths of children under five years of age each year. The large number of serotypes underlying the disease spectrum, which would be reflected in the high production cost of a commercial vaccine effective to protect against all of them and the higher level of amino acid sequence conservation as compared to polysaccharide structure, has prompted us to attempt to use conserved proteins for the development of a simpler vaccine. One of the most prominent proteins is pneumolysin (Ply), present in almost all the serotypes known at the moment, which shows an effective protection against S. pneumoniae infections.

Results

We have cloned the pneumolysin gene from S. pneumoniae serotype 14 and studied the effects of eight variables related to medium composition and induction conditions on the soluble expression of rPly in Escherichia coli (E. coli) and a 2^8-4 factorial design was applied. Statistical analysis was carried out to compare the conditions used to evaluate the expression of soluble pneumolysin; rPly activity was evaluated by hemolytic activity assay and served as the main response to evaluate the proper protein expression and folding. The optimized conditions, validated by the use of triplicates, include growth until an absorbance of 0.8 (measured at 600 nm) with 0.1 mM IPTG during 4 h at 25°C in a 5 g/L yeast extract, 5 g/L tryptone, 10 g/L NaCl, 1 g/L glucose medium, with addition of 30 μg/mL kanamycin.

Conclusions

This experimental design methodology allowed the development of an adequate process condition to attain high levels (250 mg/L) of soluble expression of functional rPly in E. coli, which should contribute to reduce operational costs. It was possible to recover the protein in its active form with 75% homogeneity.

Cost-effective production of recombinant human interleukin 24 by lactose induction and a two-step denaturing and one-step refolding method

Recombinant human interleukin 24 (rhIL24) is a member of the interleukin 10 (IL10) family of cytokines with novel therapeutic properties. Human IL24 possesses three N glycosylation sites and a disulfide bridge. The cost and composition of culture media is critical for commercial-scale production of recombinant proteins in E. coli. Addition of yeast extract and glucose to medium enhances rhIL24 production, and the use of lactose instead of IPTG for induction drops the cost and decreases toxicity. In addition, a two-step denaturing and one-step refolding (2DR) strategy improves rhIL24 production. The 2DR strategy replaces a more conventional approach for protein solubilization and refolding. LC–MS/MS provides definitive identification and quantitative information on rhIL24. Single-step purified rhIL24 displayed biological activity on HepG2 hepatocellular carcinoma cells, but no effect on L02 cells. Proliferation analysis suggests that rhIL24 may have potential use as a medication. In the present study, we developed a simple process for producing quality product with high purity. The expression and purification of rhIL24 described here may be a step towards inexpensive large-scale production.

Controllable production of low molecular weight heparins by combinations of heparinase I/II/III

Enzymatic depolymerization of heparin by heparinases is promising for production of low molecular weight heparins (LMWHs) as anticoagulants, due to its mild reaction conditions and high selectivity. Here, different heparinase combinations were used to depolymerize heparin. Heparinase I and heparinase II can depolymerize heparin more efficiently than heparinase III, respectively, but heparinase III was the best able to protect the anticoagulant activities of LMWHs. Heparinase III and heparinase I/II combinations were able to efficiently depolymerize heparin to LMWHs with higher anticoagulant activity than the LMWHs produced by the respective heparinase I and heparinase II. HepIII and HepI is the best combination for maintaining high anti-IIa activity (75.7 ± 4.21 IU/mg) at the same Mw value. Furthermore, considering both the changes in molecular weight and anticoagulant activity, the action patterns of heparinase I and heparinase II were found not to follow the exolytic and processive depolymerizing mechanism from the reducing end of heparin.

Rational design of a tripartite fusion protein of heparinase I enables one-step affinity purification and real-time activity detection

Enzymatic degradation of heparin has great potential as an ecological and specific way to produce low molecular weight heparin. However, the commercial use of heparinase I (HepA), one of the most important heparin lyases, has been hampered by low productivity and poor thermostability. Fusion with green fluorescent protein (GFP) or maltose-binding protein (MBP) has shown potential in facilitating the industrial use of HepA. Thus, tripartite fusion of GFP, MBP and HepA would be a promising approach. Therefore, in the present study, the tripartite fusion strategy was systematically studied, mainly focusing on the fusion order and the linker sequence, to obtain a fusion protein offering one-step purification and real-time detection of HepA activity by fluorescence as well as high HepA activity and thermostability. Our results show that fusion order is important for MBP binding affinity and HepA activity, while the linker sequences at domain junctions have significant effects on protein expression level, HepA activity and thermostability as well as GFP fluorescence. The best tripartite fusion was identified as MBP-(EAAAK)(3)-GFP-(GGGGS)(3)-HepA, which shows potential to facilitate the production of HepA and its application in industrial preparation of low molecular weight heparin.

Combination of site-directed mutagenesis and calcium ion addition for enhanced production of thermostable MBP-fused heparinase I in recombinant Escherichia coli

Heparinase I (HepI), which specifically cleaves heparin and heparan sulfate, is one of the most extensively studied glycosaminoglycan lyases. Low productivity of HepI has largely hindered its industrial and pharmaceutical applications. Loss of bacterial HepI enzyme activity through poor thermostability during its expression and purification process in production can be an important issue. In this study, using a thermostabilization strategy combining site-directed mutagenesis and calcium ion addition during its production markedly improved the yield of maltose-binding protein-fused HepI (MBP-HepI) from recombinant Escherichia coli. Substitution of Cys297 to serine in MBP-HepI offered a 30.6% increase in the recovered total enzyme activity due to a mutation-induced thermostabilizing effect. Furthermore, upon addition of Ca2+ as a stabilizer at optimized concentrations throughout its expression, extraction, and purification process, purified mutant MBP-HepI showed a specific activity of 56.3 IU/mg, 206% higher than that of the wild type obtained without Ca2+ addition, along with a 177% increase in the recovered total enzyme activity. The enzyme obtained through this novel approach also exhibited significantly enhanced thermostability, as indicated by both experimental data and the kinetic modeling. High-yield production of thermostable MBP-HepI using the present system will facilitate its applications in laboratory-scale heparin analysis as well as industrial-scale production of low molecular weight heparin as an improved anticoagulant substitute.

Enhanced soluble expression of recombinant Flavobacterium heparinum heparinase I in Escherichia coli by fusing it with various soluble partners

Heparinase I (HepA) was originally isolated from Flavobacterium heparinum (F. heparinum) and specifically cleaves heparin/heparan sulfate in a site-dependent manner, showing great promise for producing low molecular weight heparin (LMWH). However, expressing recombinant HepA is extremely difficult in Escherichia coli because it suffers from low yields, insufficient purity and insolubility. In this paper, we systematically cloned and fused the HepA gene to the C-terminus of five soluble partners, including translation initiation factor 2 domain I (IF2), glutathione S-transferase (GST), maltose-binding protein (MBP), small ubiquitin modifying protein (SUMO) and N-utilization substance A (NusA), to screen for their abilities to improve the solubility of recombinant HepA when expressed in E. coli. A convenient two-step immobilized metal affinity chromatography (IMAC) method was utilized to purify these fused HepA hybrids. We show that, except for NusA, the fusion partners dramatically improved the soluble expression of recombinant HepA, with IF2-HepA and SUMO-HepA creating almost completely soluble HepA (98% and 94% of expressed HepA fusions are soluble, respectively), which is the highest yield rate published to the best of our knowledge. Moreover, all of the fusion proteins show comparable biological activity to their unfused counterparts and could be used directly without removing the fusion tags. Together, our results provide a viable option to produce large amounts of soluble and active recombinant HepA for manufacturing.

Optimization of medium formulation and seed conditions for expression of mature PsaA (pneumococcal surface adhesin A) in Escherichia coli using a sequential experimental design strategy and response surface methodology

PsaA, a candidate antigen for a vaccine against pneumonia, is well-conserved in all Streptococcus pneumoniae serotypes. A sequence of two-level experimental designs was used to evaluate medium composition and seed conditions to optimize the expression of soluble mature PsaA in E. coli. A face-centered central composite design was first used to evaluate the effects of yeast extract (5 and 23.6 g/L), tryptone (0 and 10 g/L), and glucose (1 and 10 g/L), with replicate experiments at the central point (14.3 g/L yeast extract, 5 g/L tryptone, 5.5 g/L glucose). Next, a central composite design was used to analyze the influence of NaCl concentration (0, 5, and 10 g/L) compared with potassium salts (9.4 g/L K(2)HPO(4)/2.2 g/L KH(2)PO(4)), and seed growth (7 and 16 h). Tryptone had no significant effect and was removed from the medium. Yeast extract and glucose were optimized at their intermediate concentrations, resulting in an animal-derived material-free culture medium containing 15 g/L yeast extract, 8 g/L glucose, 50 μg/mL kanamycin, and 0.4% glycerol, yielding 1 g/L rPsaA after 16 h induction at 25°C in shake flasks at 200 rpm. All the seed age and salt conditions produced similar yields, indicating that no variation had a statistically significant effect on expression. Instead of growing the seed culture for 16 h (until saturation), the process can be conducted with 7 h seed growth until the exponential phase. These results enhanced the process productivity and reduced costs, with 5 g/L NaCl being used rather than potassium salts.

Influence of induction conditions on the expression of carbazole dioxygenase components (CarAa, CarAc, and CarAd) from Pseudomonas stutzeri in recombinant Escherichia coli using experimental design

Carbazole 1,9a-dioxygenase (CarA), the first enzyme in the carbazole degradation pathway used by Pseudomonas sp., was expressed in E. coli under different conditions defined by experimental design. This enzyme depends on the coexistence of three components containing [2Fe-2S] clusters: CarAa, CarAc, and CarAd. The catalytic site is present in CarAa. The genes corresponding to components of carbazole 1,9a-dioxygenase from P. stutzeri were cloned and expressed by salt induction in E. coli BL21-SI (a host that allows the enhancement of overexpressed proteins in the soluble fraction), using the vector pDEST™14. The expression of these proteins was performed under different induction conditions (cell concentration, temperature, and time), with the help of two-level factorial design. Cell concentration at induction (measured by absorbance at 600 nm) was tested at 0.5 and 0.8. After salt induction, expression was performed at 30 and 37°C, for 4 h and 24 h. Protein expression was evaluated by densitometry analysis. Expression of CarAa was enhanced by induction at a lower cell concentration and temperature and over a longer time, according to the analysis of the experimental design results. The results were validated at Abs (ind) = 0.3, 25°C, and 24 h, at which CarAa expression was three times higher than under the standard condition. The behavior of CarAc and CarAd was the inverse, with the best co-expression condition tested being the standard one (Abs (ind) = 0.5, T = 37°C, and t = 4 h). The functionality of the proteins expressed in E. coli was confirmed by the degradation of 20 ppm carbazole.

Inulinase-expressing microorganisms and applications of inulinases

In this review article, inulinase-expressing microorganisms and its potential applications in transformation of inulin into very-high-fructose syrup, bioethanol, and inulooligosaccharides are overviewed. In the past 10 years, many new inulinase producers have been obtained and many genes encoding inulinases from different microorganisms have been cloned and characterized. Some novel processes for exoinulinase overproduction have been developed for bioethanol production and ultra-high-fructose syrup. The endoinulinases have also been used for production of inulooligosaccharides from inulin and inulin-containing materials.

Enhanced inulinase production in solid state fermentation by a mutant of the marine yeast Pichia guilliermondii using surface response methodology and inulin hydrolysis

In order to isolate inulinase overproducers of the marine yeast Pichia guilliermondii, strain 1, cells were mutated by using UV light and LiCl(2). One mutant (M-30) with enhanced inulinase production was obtained. Response surface methodology (RSM) was used to optimize the medium compositions and cultivation conditions for inulinase production by the mutant in solid-state fermentation. The initial moisture, inoculum, the amount ratio of wheat bran to rice bran, temperature, pH for the maximum inulinase production by the mutant M-30 were found to be 60.5%, 2.5%, 0.42, 30 degrees C and 6.50, respectively. Under the optimized conditions, 455.9 U/grams of dry substrate (gds) of inulinase activity was reached in the solid state fermentation culture of the mutant M-30 whereas the predicted maximum inulinase activity of 459.2 U/gds was derived from RSM regression. Under the same conditions, its parent strain only produced 291.0 U/gds of inulinase activity. This is the highest inulinase activity produced by the yeast strains reported so far.

Medium optimization based on statistical methodologies for pristinamycins production by Streptomyces pristinaespiralis

The optimization of nutrient levels for the production of pristinamycins by Streptomyces pristinaespiralis CGMCC 0957 in submerged fermentation was carried out using the statistical methodologies based on the Plackett-Burman design, the steepest ascent method, and the central composite design (CCD). First, the Plackett-Burman design was applied to evaluate the influence of related nutrients in the medium. Soluble starch and MgSO4 x 7H2O were then identified as the most significant nutrients with a confidence level of 99%. Subsequently, the concentrations of the two nutrients were further optimized using response surface methodology of CCD, together with the steepest ascent method. Accordingly, a second-order polynomial regression model was finally fitted to the experimental data. By solving the regression equation from the model and analyzing the response surface, the optimal levels for soluble starch and MgSO4 x 7H2O were determined as 20.95 and 5.67g/L, respectively. Under the optimized medium, the yield of pristinamycins in the shake flask and 5-L bioreactor could reach 1.30 and 1.01 g/L, respectively, which is the highest yield reported in literature to date.