Heterologous expression and biochemical characterization of a cold-active lipase from Rhizopus microsporus suitable for oleate synthesis and bread making

OBJECTIVES

Cold-active lipases which show high specific activity at low temperatures are attractive in industrial applications in terms of product stability and energy saving. We aimed to identify novel cold-active lipase suitable for oleates synthesis and bread making.

RESULTS

A novel lipase gene (RmLipA) from Rhizopus microsporus was cloned and heterologously expressed in Pichia pastoris. The encoding sequence displayed 75% identity to the lipase from R. niveus. The highest extracellular lipase activity of 7931 U/mL was achieved in a 5-L fermentation. The recombinant enzyme (RmLipA) was optimally active at pH 8.0 and 20-25 °C, respectively, and stable over a wide pH range of 2.0-11.0. The enzyme was a cold-active lipase, exhibiting > 80% of its maximal activity at 0 °C. RmLipA was a sn-1,3 regioselective lipase, and preferred to hydrolyze pNP esters and triglycerides with relatively long chain fatty acids. RmLipA synthesized various oleates using oleic acid and different alcohols as substrates (> 95%). Moreover, it significantly improved the quality of bread by increasing its specific volume (21.7%) and decreasing its crumb firmness (28.6%).

CONCLUSIONS

A novel cold-active lipase gene from R. microsporus was identified, and its application potentials were evaluated. RmLipA should be a potential candidate in oleates synthesis and bread making industries.

Lipase-Catalyzed Chemoselective Ester Hydrolysis of Biomimetically Coupled Aryls for the Synthesis of Unsymmetric Biphenyl Esters

Lipases are among the most frequently used biocatalysts in organic synthesis, allowing numerous environmentally friendly and inexpensive chemical transformations. Here, we present a biomimetic strategy based on iron(III)-catalyzed oxidative coupling and selective ester monohydrolysis using lipases for the synthesis of unsymmetric biphenyl-based esters under mild conditions. The diverse class of biphenyl esters is of pharmaceutical and technical relevance. We explored the potency of a series of nine different lipases of bacterial, fungal, and mammalian origin on their catalytic activities to cleave biphenyl esters, and optimized the reaction conditions, in terms of reaction time, temperature, pH, organic solvent, and water–organic solvent ratios, to improve the chemoselectivity, and hence control the ratio of unsymmetric versus symmetric products. Elevated temperature and increased DMSO content led to an almost exclusive monohydrolysis by the four lipases Candida rugosa lipase (CRL), Mucor miehei lipase (MML), Rhizopus niveus lipase (RNL), and Pseudomonas fluorescens lipase (PFL). The study was complemented by in silico binding predictions to rationalize the observed differences in efficacies of the lipases to convert biphenyl esters. The optimized reaction conditions were transferred to the preparative scale with high yields, underlining the potential of the presented biomimetic approach as an alternative strategy to the commonly used transition metal-based strategies for the synthesis of diverse biphenyl esters.

Structural Basis by Which the N-Terminal Polypeptide Segment of Rhizopus chinensis Lipase Regulates Its Substrate Binding Affinity

Members of an important group of industrial enzymes, Rhizopus lipases, exhibit valuable hydrolytic features that underlie their biological functions. Particularly important is their N-terminal polypeptide segment (NTPS), which is required for secretion and proper folding but is removed in the process of enzyme maturation. A second common feature of this class of lipases is the α-helical "lid", which regulates the accessibility of the substrate to the enzyme active site. Some Rhizopus lipases also exhibit "interfacial activation" by micelle and/or aggregate surfaces. While it has long been recognized that the NTPS is critical for function, its dynamic features have frustrated efforts to characterize its structure by X-ray crystallography. Here, we combine nuclear magnetic resonance spectroscopy and X-ray crystallography to determine the structure and dynamics of Rhizopus chinensis lipase (RCL) with its 27-residue NTPS prosequence (r27RCL). Both r27RCL and the truncated mature form of RCL (mRCL) exhibit biphasic interfacial activation kinetics with p-nitrophenyl butyrate (pNPB). r27RCL exhibits a substrate binding affinity significantly lower than that of mRCL due to stabilization of the closed lid conformation by the NTPS. In contrast to previous predictions, the NTPS does not enhance lipase activity by increasing surface hydrophobicity but rather inhibits activity by forming conserved interactions with both the closed lid and the core protein structure. Single-site mutations and kinetic studies were used to confirm that the NTPS serves as internal competitive inhibitor and to develop a model of the associated process of interfacial activation. These structure-function studies provide the basis for engineering RCL lipases with enhanced catalytic activities.

CRISPR-Cas9 induces point mutation in the mucormycosis fungus Rhizopus delemar

Rhizopus delemar causes devastating mucormycosis in immunodeficient individuals. Despite its medical importance, R. delemar remains understudied largely due to the lack of available genetic markers, the presence of multiple gene copies due to genome duplication, and mitotically unstable transformants resulting from conventional and limited genetic approaches. The clustered regularly interspaced short palindromic repeat (CRISPR)-associated nuclease 9 (Cas9) system induces efficient homologous and non-homologous break points and generates individual and multiple mutant alleles without requiring selective marker genes in a wide variety of organisms including fungi. Here, we have successfully adapted this technology for inducing gene-specific single nucleotide (nt) deletions in two clinical strains of R. delemar: FGSC-9543 and CDC-8219. For comparative reasons, we first screened for spontaneous uracil auxotrophic mutants resistant to 5-fluoroorotic acid (5-FOA) and obtained one substitution (f1) mutationin the FGSC-9543 strain and one deletion (f2) mutation in the CDC-8219 strain. The f2 mutant was then successfully complemented with a pyrF-dpl200 marker gene. We then introduced a vector pmCas9:tRNA-gRNA that expresses both Cas9 endonuclease and pyrF-specific gRNA into FGSC-9543 and CDC-8219 strains and obtained 34 and 42 5-FOA resistant isolates, respectively. Candidate transformants were successively transferred eight times by propagating hyphal tips prior to genotype characterization. Sequencing of the amplified pyrF allele in all transformants tested revealed a single nucleotide (nt) deletion at the 4th nucleotide before the protospacer adjacent motif (PAM) sequence, which is consistent with CRISPR-Cas9 induced gene mutation through non-homologous end joining (NHEJ). Our study provides a new research tool for investigating molecular pathogenesis mechanisms of R. delemar while also highlighting the utilization of CRISPR-Cas9 technology for generating specific mutants of Mucorales fungi.

Protection effect of polyols on Rhizopus chinensis lipase counteracting the deactivation from high pressure and high temperature treatment

The influence of polyols on Rhizopus chinensis lipase (RCL) was investigated under high pressure. The poor stability of RCL was observed at 500 MPa at 60 °C without polyols which protected RCL against the loss of activity. The lipase is more stable in phosphate buffer than in tris buffer despite the protection of polyols. The activity was maintained 63% by the sorbitol of 2 mol/L in Tris-HCl buffer but 73% in phosphate buffer after the treatment at 500 MPa and 60 °C for 25 min. The same protective effects could be observed at 1 mol/L of sorbitol, erythritol, xylitol, and mannitol. However, further increase of hydroxyl group number could not significantly improve the enzyme stability. The protection of polyols on RCL appears to depend on both of the polyol nature and the hydroxyl group number. Together with fluorescence spectra, circular dichroism spectra indicated that the chaotic conformation of RCL under high pressure became more ordered with 1 mol/L sorbitol. The results showed that sorbitol effectively stabilized the lipase conformation including the hydrophobic core under extreme conditions. It might be attributed to the interaction of polyols with RCL surface to modify intra-/intermolecular hydrogen bonds, maintaining the hydrophobic interactions within RCL.

Fumaric acid production using renewable resources from biodiesel and cane sugar production processes

The microbial production of fumaric acid by Rhizopus arrhizus NRRL 2582 has been evaluated using soybean cake from biodiesel production processes and very high polarity (VHP) sugar from sugarcane mills. Soybean cake was converted into a nutrient-rich hydrolysate via a two-stage bioprocess involving crude enzyme production via solid state fermentations (SSF) of either Aspergillus oryzae or R. arrhizus cultivated on soybean cake followed by enzymatic hydrolysis of soybean cake. The soybean cake hydrolysate produced using crude enzymes derived via SSF of R. arrhizus was supplemented with VHP sugar and evaluated using different initial free amino nitrogen (FAN) concentrations (100, 200, and 400 mg/L) in fed-batch cultures for fumaric acid production. The highest fumaric acid concentration (27.3 g/L) and yield (0.7 g/g of total consumed sugars) were achieved when the initial FAN concentration was 200 mg/L. The combination of VHP sugar with soybean cake hydrolysate derived from crude enzymes produced by SSF of A. oryzae at 200 mg/L initial FAN concentration led to the production of 40 g/L fumaric acid with a yield of 0.86 g/g of total consumed sugars. The utilization of sugarcane molasses led to low fumaric acid production by R. arrhizus, probably due to the presence of various minerals and phenolic compounds. The promising results achieved through the valorization of VHP sugar and soybean cake suggest that a focused study on molasses pretreatment could lead to enhanced fumaric acid production.

Continuous ethyl oleate synthesis by lipases produced by solid-state fermentation by Rhizopus microsporus

Lipases produced by solid-state fermentation were used directly as biocatalysts for continuous synthesis of ethyl oleate in a continuously stirred tank reactor. The effect of biocatalyst reutilisation, molar ratio of substrates, agitation rate and feed rate on the esterification of oleic acid with ethanol were investigated. The catalyst maintained 90% conversion for four batch cycles with a 1:2 molar ratio (oleic acid:ethanol). Mechanical agitation at 200 and 300 rpm during 12 h of continuous reaction did not affect the biocatalytic conversion, allowing substrate conversions greater than 90% that were obtained with 50 mM oleic acid at a molar ratio of 1:2 during 14 h reaction. In contrast, substrate conversion was 70% with 100 mM oleic acid at a flow rate of 2 mL/min during 25 h of reaction. These results are promising and offer a technical alternative for the development of accessible biocatalysts that can be used in continuous operations.

The growth of Pichia pastoris Mut+ on methanol-glycerol mixtures fits to interactive dual-limited kinetics: model development and application to optimised fed-batch operation for heterologous protein production

The methanol-glycerol co-feeding during the induction stage for heterologous protein production in Pichia pastoris has shown significant productive applications. Available model analysis applied to this dual-limited condition is scarce and normally does not consider the interaction effects between the substrates. In this work, a dual-limited growth model of P. pastoris considering an interactive kinetic effect was applied to an optimised fed-batch process production of heterologous Rhizopus oryzae lipase (ROL). In the proposed model, the growth kinetics on glycerol is fully expressed, whereas methanol kinetics is modulated by the co-metabolisation of glycerol, resulting in an enhancing effect of glycerol-specific growth rate. The modelling approach of fed-batch cultures also included the methanol volatilisation caused by the aeration that was found to be a not-negligible phenomenon. The model predicts the ability of P. pastoris to keep control of the methanol concentration in the broth during ROL-optimised production process in fed batch and fits satisfactorily the specific cell growth rate and ROL production. Implications of interaction effect are discussed applying the general procedure of modelling approach.

Improvement of enzymatic properties of Rhizopus oryzae α-amylase by site-saturation mutagenesis of histidine 286

Optimal pH and ideal functioning temperature for fungal α-amylase can greatly contribute to improving enzyme efficiency in maltose-forming ability. This work aimed to improve the enzymatic properties of Rhizopus oryzae α-amylase by site-saturation mutagenesis of histidine 286. The biochemical properties of selected mutant enzymes were modified to increase their enzymatic efficiencies compared to their wild-type counterparts. For instance, the optimum temperature of mutants H286 L, H286I, H286S and H286 T was increased from 50 °C to 55 °C, while a similar increase was observed for H286 P from 50 °C to 60 °C. The optimum pH of mutants H286 L, H286I and H286D shifted from 5.5 to 5.0, and the optimum pH of mutant H286E shifted from 5.5 to 4.5. The results obtained showed that the mutant H286I showed a 1.5-fold increase in half-life at 55 °C and the mutant H286E showed a 6.43-fold increase in half-life at a pH of 4.5. Furthermore, the ability to form maltose from soluble starch for mutants H286 L and H286 M was significantly improved under the optimum conditions determined in the study. The catalytic mechanism responsible for improved maltose-forming ability was confirmed through molecular docking simulations with maltotriose among wild-type and mutant enzymes. The mutants with improved enzymatic properties that were attained in this work may help in future computer-aided directed evolution of fungal α-amylase.

Backbone and Ile-δ1, Leu, Val methyl 1H, 15N, and 13C, chemical shift assignments for Rhizopus chinensis lipase

Lipase r27RCL is a 296-residue, 33 kDa monomeric enzyme with high ester hydrolysis activity, which has significant applications in the baking, paper and leather industries. The lipase gene proRCL from Rhizopus microsporus var. chinensis (also Rhizopus chinensis) CCTCC M201021 was cloned as a fusion construct C-terminal to a maltose-binding protein (MBP) tag, and expressed as MBP-proRCL in an Escherichia coli BL21 trxB (DE3) expression system with uniform ²H,¹³C,¹⁵N-enrichment and Ile-δ1, Leu, and Val ¹³CH₃ methyl labeling. The fusion protein was hydrolyzed by Kex2 protease at the recognition site Lys-Arg between residues -29 and -28 of the prosequence, producing the enzyme form called r27RCL. Here we report extensive backbone ¹H, ¹⁵N, and ¹³C, as well as Ile-δ1, Leu, and Val side chain methyl, NMR resonance assignments for r27RCL.

High-level extracellular production of Rhizopus oryzae lipase in Pichia pastoris via a strategy combining optimization of gene-copy number with co-expression of ERAD-related proteins

Rhizopus oryzae lipase (ROL) is an important industrial enzyme limited in application due to its low production in native strains. Here, we used a new combined strategy to overexpress ROL in Pichia pastoris. An efficient method based on bio-brick was developed to construct a series of vectors harboring different copy numbers of ROL gene cassettes, which were then transformed into P. pastoris GS115 to generate a strain with specific copy numbers of ROL. An optimized gene-dosage recombinant strain of GS115/pAOα-5ROL 11# harboring five copies of ROL was screened, revealing production of the highest activity (2700 U/mL), which was 8-fold higher than that of the strain harboring one copy. The activity of GS115/pAOα-5ROL 11# was then enhanced to 3080 U/mL in a shaking flask under optimized culture conditions. Subsequently, the endoplasmic reticulum-associated protein-degradation-related genes Ubc1 or/and Hrd1 were co-expressed with ROL to further increase ROL expression. The activities of the recombinant strains, GS115/5ROL-Ubc1 22#, -Hrd1 15#, and -Hrd1-Ubc1 1#, were 4000 U/mL, 4200 U/mL, and 4750 U/mL, which was 29.9%, 36.4%, and 54.2% higher, respectively, than that observed in GS115/pAOα-5ROL 11#. Using the combined strategy, ROL expression was improved 15.8-fold, with maximum GS115/5ROL-Hrd1-Ubc1 1# activity reaching 33,900 U/mL via a sorbitol/methanol co-feeding strategy in a 3-L fermenter and resulting in a 1.65-, 1.26-, and 1.14-fold enhancement relative to the activities observed in strains GS115/pAOα-5ROL 11#, GS115/5ROL-Ubc1 22#, and GS115/5ROL-Hrd1 15#, respectively. These results indicated that heterologous overexpression of ROL in P. pastoris using this combined strategy is feasible for large-scale industrialization.

Recent Advances in Pichia pastoris as Host for Heterologous Expression System for Lipases: A Review

The production of heterologous lipases is one of the most promising strategies to increase the productivity of the bioprocesses and to reduce costs, with the final objective that more industrial lipase applications could be implemented.In this chapter, an overview of the new success in synthetic biology, with traditional molecular genetic techniques and bioprocess engineering in the last 5 years in the cell factory Pichia pastoris, the most promising host system for heterologous lipase production, is presented.The goals get on heterologous Candida antarctica, Rhizopus oryzae, and Candida rugosa lipases, three of the most common lipases used in biocatalysis, are showed. Finally, new cell factories producing heterologous lipases are presented.

Coupled effects of salt and pressure on catalytic ability of Rhizopus chinensis lipase

BACKGROUND

Both high pressure and environmental factors could influence the catalytic abilities of enzymes. This work investigated coupled effects of pressure and salts on Rhizopus chinensis lipase (RCL) to provide significant information for its further applications.

RESULTS

The maximum activity of RCL was observed under 200 MPa at 40 °C. The highest activity was achieved at concentrations of 0.06-0.1 mol L^-1 for tested salts. The effect of monovalent cations on RCL activity followed the Hofmeister series (K⁺ > Na⁺ > Li⁺ ) at 0.1 MPa but the order of Na⁺ and K⁺ was changed under 200 MPa. Meanwhile, the effects of anions did not follow the Hofmeister series. KCl slightly improved the thermostability of RCL at moderate concentration. At 60 °C, LiCl only stabilised RCL at 0.1 mol L^-1 . The pre-transition unfolding point was shifted from 4.5 to 3.5 mol L^-1 with pressure increasing from 0.1 to 600 MPa. In addition, KCl could not change the lipase's extrinsic fluorescence evolution versus pressure.

CONCLUSION

Pressure and salts could improve catalytic ability and stability of RCL under appropriate conditions. The effect of high pressure on RCL was influenced by salts. Meanwhile salts cannot prevent high pressure-induced damage to RCL. © 2017 Society of Chemical Industry.

Selective degradation of the recalcitrant cell wall of Scenedesmus quadricauda CASA CC202

An eco-friendly cell wall digestion strategy was developed to enhance the availability of nutritionally important bio molecules of edible microalgae and exploit them for cloning, transformation, and expression of therapeutic proteins. Microalgae are the source for many nutritionally important bioactive compounds and potential drugs. Even though edible microalgae are rich in nutraceutical, bioavailability of all these molecules is very less due to their rigid recalcitrant cell wall. For example, the cell wall of Scenedesmus quadricauda CASA CC202 is made up of three layers comprising of rigid outer pectin and inner cellulosic layer separated by a thin middle layer. In the present investigation, a comprehensive method has been developed for the selective degradation of S. quadricauda CASA CC202 cell wall, by employing both mechanical and enzymatic treatments. The efficiency of cell wall removal was evaluated by measuring total reducing sugar (TRS), tannic acid-ferric chloride staining, calcoflour white staining, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) analysis. It was confirmed that the yield of TRS increased from 129.82 mg/g in 14 h from pectinase treatment alone to 352.44 mg/g by combined sonication and enzymatic treatment within 12 h. As a result, the combination method was found to be effective for the selective degradation of S. quadricauda CASA CC202 cell wall. This study will form a base for our future works, where this will help to enhance the digestibility and availability of nutraceutically important proteins.

N-Glycosylation Engineering to Improve the Constitutive Expression of Rhizopus oryzae Lipase in Komagataella phaffii

Our previous studies demonstrated that the N-glycans in Rhizopus chinensis lipase (RCL) was important for its secretion. In order to improve the secretion of Rhizopus oryzae lipase (ROL) under the control of the GAP promoter in Komagataella phaffii, two extra N-glycosylation sites were introduced in ROL according to the position of the N-glycosylation sites of RCL by sequence alignment. The results indicated that the secretion level of ROL was strongly improved by N-glycosylation engineering, and the highest value of extracellular enzyme activity was increased from 0.4 ± 0.2 U/mL to 207 ± 6 U/mL in a shake flask. In the 7-L fermenter, the extracellular enzyme activity of the mutant (2600 ± 43 U/mL) and the total protein concentration (2.5 ± 0.2 g/L) were 218- and 6.25-fold higher than these of the parent, respectively. This study presents a strategy for constitutive recombinant expression of ROL using the GAP promoter combined with N-glycosylation engineering, providing a potential enzyme for application in the food industry.

Efficient Synthesis of Glucosyl-β-Cyclodextrin from Maltodextrins by Combined Action of Cyclodextrin Glucosyltransferase and Amyloglucosidase

Instead of β-cyclodextrin (β-CD), branched β-CDs have been increasingly used in many aspects as they possess better solubility and higher bioadaptability. But most commercialized branched β-CDs were chemically synthesized. Thus, the glucosyl-β-cyclodextrin (G₁-β-CD) prepared via enzymatic approach could be a nice substitute. However, the yield of G₁-β-CD was low. Here, we reported a controlled two-step reaction to efficiently prepare G₁-β-CD from maltodextrins by β-cyclodextrin glucosyltransferase (β-CGTase) and amyloglucosidase (AG). Compared to the single β-CGTase reaction, controlled two-step reaction caused a yield increase of G₁-β-CD by 130%. Additionally, the percentage of G₁-β-CD was enhanced from 2.4% to 24.0% and the side products α-CD and γ-CD were hydrolyzed because of the coupling activity of β-CGTase. Thus, this controlled two-step reaction might be an efficient approach for industrial production of pure G₁-β-CD.

Green Synthesis of Conjugated Linoleic Acids from Plant Oils Using a Novel Synergistic Catalytic System

A novel and efficient method has been developed for converting plant oil into a specific conjugated linoleic acid (CLA) using a synergistic biocatalytic system based on immobilized Propionibacterium acnes isomerase (PAI) and Rhizopus oryzae lipase (ROL). PAI exhibited the greatest catalytic activity when immobilized on D301R anion-exchange resin under optimal conditions (PAI dosage of 12 410 U of PAI/g of D301R, glutaraldehyde concentration of 0.4%, and reaction conditions of pH 7.0, 25 °C, and 60 min). Up to 109 g/L trans-10,cis-12-CLA was obtained after incubation of 200 g/L sunflower oil with PAI (1659 U/g of oil) and ROL (625 mU/g of oil) at pH 7.0 and 35 °C for 36 h; the corresponding conversion ratio of linoleic acid (LA) to CLA was 90.5%. This method exhibited the highest proportion of trans-10,cis-12-CLA yet reported and is a promising method for large-scale production.

Fungal Glycolipid Hydrolase Inhibitors and Their Effect on Cryptococcus neoformans

Pathogenic fungi kill an estimated 1.3 million people each year. This number is predicted to rise as drug resistance spreads, thus antifungal drugs with novel modes of action are urgently required. Fungal endoglycoceramidase-related proteins 1 and 2 (EGCrP-1 and -2), which hydrolyse glucosylceramide and ergosteryl β-glucoside, respectively, are important for fungal cell growth and have been identified as potential targets for drug development. A library of iminosugar derivatives was screened against EGCrP-1 and -2, and a number of competitive inhibitors with nanomolar affinities were identified. In addition, a mechanism-based inhibitor was shown to form a covalent derivative with EGCrP-2. Nine of the inhibitors were evaluated against Cryptococcus neoformans. Several showed growth inhibitory activity, but only against a C. neoformans strain lacking the outer fungal polysaccharide capsule; this implies that penetration into the cell is a significant handicap for these inhibitors. Pro-drug versions of these inhibitors could address this issue.

Fumarate Production by Torulopsis glabrata: Engineering Heterologous Fumarase Expression and Improving Acid Tolerance

Fumarate is a well-known biomass building block compound. However, the poor catalytic efficiency of fumarase is one of the major factors preventing its widespread production. To address this issue, we selected residues 159HPND162 of fumarase from Rhizopus oryzae as targets for site-directed mutagenesis based on molecular docking analysis. Twelve mutants were generated and characterized in detail. Kinetic studies showed that the Km values of the P160A, P160T, P160H, N161E, and D162W mutants were decreased, whereas Km values of H159Y, H159V, H159S, N161R, N161F, D162K, and D162M mutants were increased. In addition, all mutants displayed decreased catalytic efficiency except for the P160A mutant, whose kcat/Km was increased by 33.2%. Moreover, by overexpressing the P160A mutant, the engineered strain T.G-PMS-P160A was able to produce 5.2 g/L fumarate. To further enhance fumarate production, the acid tolerance of T.G-PMS-P160A was improved by deleting ade12, a component of the purine nucleotide cycle, and the resulting strain T.G(△ade12)-PMS-P160A produced 9.2 g/L fumarate. The strategy generated in this study opens up new avenues for pathway optimization and efficient production of natural products.

Efficient regioselective acylation of quercetin using Rhizopus oryzae lipase and its potential as antioxidant

The present investigation describes the regioselective enzymatic acylation of quercetin with ferulic acid using Rhizopus oryzae lipase. Optimization of reaction parameters resulted in 93.2% yield of the ester synthesized using 750IU of lipase in cyclo-octane at a temperature of 45°C. The reaction was successfully carried out upto 25g scale. The ester synthesized was analyzed by (1)H Nuclear magnetic resonance spectroscopy. The ester synthesized (quercetin ferulate) showed higher antiradical activity as compared to ascorbic acid using the 2,2-diphenyl-1-picrylhydrazyl radical method. These results on enzyme-catalyzed acylation of quercetin might be used to prepare and scale-up other flavonoids derivatives.

Biodiesel production from crude Jatropha oil catalyzed by non-commercial immobilized heterologous Rhizopus oryzae and Carica papaya lipases

The aim of this study was to evaluate the feasibility of biodiesel production by transesterification of Jatropha oil with methanol, catalyzed by non-commercial sn-1,3-regioselective lipases. Using these lipases, fatty acid methyl esters (FAME) and monoacylglycerols are produced, avoiding the formation of glycerol as byproduct. Heterologous Rhizopus oryzae lipase (rROL) immobilized on different synthetic resins and Carica papaya lipase (rCPL) immobilized on Lewatit VP OC 1600 were tested. Reactions were performed at 30°C, with seven stepwise methanol additions. For all biocatalysts, 51-65% FAME (theoretical maximum=67%, w/w) was obtained after 4h transesterification. Stability tests were performed in 8 or 10 successive 4h-batches, either with or without rehydration of the biocatalyst between each two consecutive batches. Activity loss was much faster when biocatalysts were rehydrated. For rROL, half-life times varied from 16 to 579h. rROL on Lewatit VPOC 1600 was more stable than for rCPL on the same support.

Efficient production of (2)H, (13)C, (15)N-enriched industrial enzyme Rhizopus chinensis lipase with native disulfide bonds

BACKGROUND

In order to use most modern methods of NMR spectroscopy to study protein structure and dynamics, isotope-enriched protein samples are essential. Especially for larger proteins (>20 kDa), perdeuterated and Ile (δ1), Leu, and Val methyl-protonated protein samples are required for suppressing nuclear relaxation to provide improved spectral quality, allowing key backbone and side chain resonance assignments needed for protein structure and dynamics studies. Escherichia coli and Pichia pastoris are two of the most popular expression systems for producing isotope-enriched, recombinant protein samples for NMR investigations. The P. pastoris system can be used to produce (13)C, (15)N-enriched and even (2)H,(13)C, (15)N-enriched protein samples, but efficient methods for producing perdeuterated proteins with Ile (δ1), Leu and Val methyl-protonated groups in P. pastoris are still unavailable. Glycosylation heterogeneity also provides challenges to NMR studies. E. coli expression systems are efficient for overexpressing perdeuterated and Ile (δ1), Leu, Val methyl-protonated protein samples, but are generally not successful for producing secreted eukaryotic proteins with native disulfide bonds.

RESULTS

The 33 kDa protein-Rhizopus chinensis lipase (RCL), an important industrial enzyme, was produced using both P. pastoris and E. coli BL21 trxB (DE3) systems. Samples produced from both systems exhibit identical native disulfide bond formation and similar 2D NMR spectra, indicating similar native protein folding. The yield of (13)C, (15)N-enriched r27RCL produced using P. pastoris was 1.7 times higher that obtained using E. coli, while the isotope-labeling efficiency was ~15 % lower. Protein samples produced in P. pastoris exhibit O-glycosylation, while the protein samples produced in E. coli were not glycosylated. The specific activity of r27RCL from P. pastoris was ~1.4 times higher than that produced in E. coli.

CONCLUSIONS

These data demonstrate efficient production of (2)H, (13)C, (15)N-enriched, Ile (δ1), Leu, Val methyl-protonated eukaryotic protein r27RCL with native disulfides using the E. coli BL21 trxB (DE3) system. For certain NMR studies, particularly efforts for resonance assignments, structural studies, and dynamic studies, E. coli provides a cost-effective system for producing isotope-enriched RCL. It should also be potential for producing other (2)H, (13)C, (15)N-enriched, Ile (δ1), Leu, Val methyl-protonated eukaryotic proteins with native disulfide bonds.

Biodiesel production from Nannochloropsis gaditana lipids through transesterification catalyzed by Rhizopus oryzae lipase

Biodiesel (fatty acid methyl esters, FAMEs) was produced from saponifiable lipids (SLs) extracted from wet Nannochloropsis gaditana biomass using methanolysis catalyzed by Rhizopus oryzae intracellular lipase. SLs were firstly extracted with ethanol to obtain 31 wt% pure SLs. But this low SL purity also gave a low biodiesel conversion (58%). This conversion increased up to 80% using SLs purified by crystallization in acetone (95 wt% purity). Polar lipids play an important role in decreasing the reaction velocity - using SLs extracted with hexane, which have lower polar lipid content (37.4% versus 49.0% using ethanol), we obtained higher reaction velocities and less FAME conversion decrease when the same lipase batch was reused. 83% of SLs were transformed to biodiesel using a 70 wt% lipase/SL ratio, 11:1 methanol/SL molar ratio, 10 mL t-butanol/g SLs after 72 h. The FAME conversion decreased to 71% after catalyzing three reactions with the same lipase batch.

Statistical optimization and mutagenesis for high level of phytase production by Rhizopus oligosporus MTCC 556 under solid state fermentation

The present study deals with production of phytase from Rhizopus oligosporus MTCC 556 by solid state fermentation (SSF) using different (ADT27, IR20, PAIYUR1, KG, and RASI) rice bran varieties, in which ADT27 rice bran yield maximum of 6.2 U gds⁻¹ phytase. Statistical optimization was employed by Central Composite Design (CCD); the results showed that 3.0 g dextrose, 2.5 g ammonium nitrate, substrate size of 80 mesh, 10 mg calcium chloride was 116 hr at optimal for phytase production by SSF, with maximum of 23.14 U gds'. Phytase production improved by 4 fold (31.3 U/gds) due to chemical mutagenesis (mutant Rhizopus oligosporus MTCC 1116) in optimized media composition. Partially purified phytase showed approximately 90 kDa of molecular mass and was optimally active at 5.5 pH and 50°C temperature. Substrate specificity exhibited in sodium phytic acid and phytase activity was stimulated by Zn²⁺ and Ca²⁺.

Purification and characterization of a cytochrome c with novel caspase-3 activation activity from the pathogenic fungus Rhizopus arrhizus

BACKGROUND

Members of Rhizopus species are the most common cause of mucormycosis, a rare but often fatal fungal infection. Host induced pathogen apoptosis and pathogen induced host cell apoptosis are often involved in fungal infections. In many organisms, the release of mitochondrial cytochrome c can trigger apoptosis by activating caspase proteases, but the role of fungal cytochrome c in apoptosis remains unknown.

RESULTS

DNA sequence encoding Rhizopus arrhizus cytochrome c was cloned and expressed in E. coli. Both native and recombinant cytochrome c were purified using ion exchange followed by gel filtration chromatography. The identities of purified proteins were confirmed by MALDI-MS and UV-Visible spectroscopy. For the first time, we demonstrated that Rhizopus arrhizus cytochrome c could activate human capspase-3 in HeLa cell extracts. We also found that Rhizopus arrhizus cytochrome c has redox potential, peroxidase activity, and spectral properties similar to human and horse cytochrome c proteins.

CONCLUSIONS

Rhizopus arrhizus cytochrome c can activate human caspase-3 in HeLa cell extracts and it possesses similar physical and spectral properties as human and horse cytochrome c. This protein was found to have a previously unknown potential to activate human caspase-3, an important step in the apoptosis cascade.

[State of Fungal Lipases of Rhizopus microsporus, Penicillium sp. and Oospora lactis in Border Layers Water-Solid Phase and Factors Affecting Catalytic Properties of Enzymes]

We demonstrated that a change in the catalytic activity of fungal lipases synthesized by Rhizopus microsporus, Penicillium sp. and Oospora lactis and their ability to absorb on different sorbents depended on the nature of groups on the solid phase surface in the model systems water: lipid and water: solid phase. Thus, the stability of Penicillium sp. lipases increased 85% in the presence ofsorsilen or DEAE-cellulose, and 55% of their initial activity respectively was preserved. In the presence of silica gel and CM-cellulose, a decreased rate of lipid hydrolysis by Pseudomonas sp. enzymes was observed in water medium, and the hydrolysis rate increased by 2.4 and 1.5 times respectively in the presence of aminoaerosil and polykefamid. In an aqueous-alcohol medium, aminoaerosil and polykefamid decreased the rate of substrate hydrolysis by more than 30 times. The addition of aerosil to aqueous and aqueous-alcohol media resulted in an increase in the hydrolysis rate by 1.2-1.3 times. Sorsilen stabilized Penicillium sp. lipase activity at 40, 45, 50 and 55 degrees C. Either stabilization or inactivation of lipases was observed depending on the pH of the medium and the nature of chemical groups localized on the surface of solid phase. The synthetizing activity of lipases also changed depending on the conditions.

Enzymatic biodiesel synthesis from yeast oil using immobilized recombinant Rhizopus oryzae lipase

The recombinant Rhizopus oryzae lipase (1-3 positional selective), immobilized on Relizyme OD403, has been applied to the production of biodiesel using single cell oil from Candida sp. LEB-M3 growing on glycerol from biodiesel process. The composition of microbial oil is quite similar in terms of saponifiable lipids than olive oil, although with a higher amount of saturated fatty acids. The reaction was carried out in a solvent system, and n-hexane showed the best performance in terms of yield and easy recovery. The strategy selected for acyl acceptor addition was a stepwise methanol addition using crude and neutralized single cell oil, olive oil and oleic acid as substrates. A FAMEs yield of 40.6% was obtained with microbial oils lower than olive oil 54.3%. Finally in terms of stability, only a lost about 30% after 6 reutilizations were achieved.

Biocatalytic behaviour of immobilized Rhizopus oryzae lipase in the 1,3-selective ethanolysis of sunflower oil to obtain a biofuel similar to biodiesel

A new biofuel similar to biodiesel was obtained in the 1,3-selective transesterification reaction of sunflower oil with ethanol using as biocatalyst a Rhizopus oryzae lipase (ROL) immobilized on Sepiolite, an inorganic support. The studied lipase was a low cost powdered enzyme preparation, Biolipase-R, from Biocon-Spain, a multipurpose additive used in food industry. In this respect, it is developed a study to optimize the immobilization procedure of these lipases on Sepiolite. Covalent immobilization was achieved by the development of an inorganic-organic hybrid linker formed by a functionalized hydrocarbon chain with a pendant benzaldehyde, bonded to the AlPO4 support surface. Thus, the covalent immobilization of lipases on amorphous AlPO4/sepiolite (20/80 wt %) support was evaluated by using two different linkers (p-hydroxybenzaldehyde and benzylamine-terephthalic aldehyde, respectively). Besides, the catalytic behavior of lipases after physical adsorption on the demineralized sepiolite  was also evaluated. Obtained results indicated that covalent immobilization with the p-hydroxybenzaldehyde linker gave the best biocatalytic behavior. Thus, this covalently immobilized lipase showed a remarkable stability as well as an excellent capacity of reutilization (more than five successive reuses) without a significant loss of its initial catalytic activity. This could allow a more efficient fabrication of biodiesel minimizing the glycerol waste production.

Study of different reaction schemes for the enzymatic synthesis of polyglycerol polyricinoleate

BACKGROUND

Different strategies for the solvent-free enzymatic production of polyglycerol polyricinoleate (PGPR) were explored in an attempt to simplify and improve the process. Besides the conventional procedure (obtaining polyricinoleic acid, followed by its esterification with polyglycerol), two alternative methods are proposed: (1) reversing the synthesis order, i.e. esterification of polyglycerol with ricinoleic acid and then the condensation of ricinoleic acid with the previously obtained polyglycerol ester; and (2) the enzymatic synthesis of PGPR in a single-step process.

RESULTS

The reaction sequences were carried out in an open-air reactor with free and immobilised lipases (triacylglycerol acylhydrolases, E.C. 3.1.1.3): Candida rugosa lipase to obtain polyricinoleic acid and Rhizopus oryzae lipase for the esterification of polyglycerol with the carboxyl group of ricinoleic or polyricinoleic acid. A co-immobilised derivative containing both lipases was used to catalyse the single-stage scheme. The three processes were carried out in a vacuum reactor, obtaining in every case PGPR that complied with the legal specifications of the European Community and recommendations provided in the Food Chemical Codex.

CONCLUSION

The results demonstrate that all three protocols are viable for the enzymatic synthesis of PGPR and require similar reaction times. The single-stage scheme is easier to carry out.

Cloning and Sequence Analysis of cDNA encodingRhizopus niveusLipase

Complementary DNA encoding Rhizopus niveus lipase (RNL) was isolated from the R. niveus IF04759 cDNA library using a synthetic oligonucleotide corresponding to the amino acid sequence of the enzyme. A clone, which had an insert of 1.0 kilobase pairs, was found to contain the coding region of the enzyme. The lipase gene was expressed in Escherichia coli as a lacZ fusion protein. The mature RNL consisted of 297 amino acid residues with a molecular mass of 32 kDa. The RNL sequence showed significant overall homology to Rhizomucor miehei lipase and the putative active site residues were strictly conserved.

[Enhanced thermostability of Rhizopus chinensis lipase by error-prone PCR]

Directed evolution was conducted to improve the thermostability of lipase from Rhizopus chinensis CCTCC M201021. Mutations were introduced by two rounds of error-prone PCR and mutant lipase was selected by fast-blue RR top agar screening. Two positive variants were selected in the first-round and four in the second-round screening process. Ep2-4 was proved as the most thermostable lipase and its DNA sequencing revealed three amino acid substitutions: A129S, P168L and V329A. Compared with the parent, its half-life at 60 degrees C was 5.4- times longer and T50 was 7.8 degrees higher. Purified lipase of Ep2-4 was characterized and the result shows that its thermostability improved without compromising enzyme activity. According to the mimicked protein structure, mutation A129S formed a hydrogen bond with Gln133 and improved the thermostability by increasing the hydrophilicity and polarity of protein; mutation P168L by forming a hydrophobic bond with the nearby Leu164.

Enhancement of lipase r27RCL production in Pichia pastoris by regulating gene dosage and co-expression with chaperone protein disulfide isomerase

Pichia pastoris has been successfully used in the production of many secreted and intracellular recombinant proteins, but there is still a large room of improvement for this expression system. Two factors drastically influence the lipase r27RCL production from Rhizopus chinensis CCTCC M201021, which are gene dosage and protein folding in the endoplasmic reticulum (ER). Regarding the effect of gene dosage, the enzyme activity for recombinant strain with three copies lipase gene was 1.95-fold higher than that for recombinant strain with only one copy lipase gene. In addition, the lipase production was further improved by co-expression with chaperone PDI involved in the disulfide bond formation in the ER. Overall, the maximum enzyme activity reached 355U/mL by the recombinant strain with one copy chaperone gene PDI plus five copies lipase gene proRCL in shaking flasks, which was 2.74-fold higher than that for the control strain with only one copy lipase gene. Overall, co-expression with PDI vastly increased the capacity for processing proteins of ER in P. pastoris.

Crystal structure of circular permuted RoCBM21 (CP90): dimerisation and proximity of binding sites

Glucoamylases, containing starch-binding domains (SBD), have a wide range of scientific and industrial applications. Random mutagenesis and DNA shuffling of the gene encoding a starch-binding domain have resulted in only minor improvements in the affinities of the corresponding protein to their ligands, whereas circular permutation of the RoCBM21 substantially improved its binding affinity and selectivity towards longer-chain carbohydrates. For the study reported herein, we used a standard soluble ligand (amylose EX-I) to characterize the functional and structural aspects of circularly permuted RoCBM21 (CP90). Site-directed mutagenesis and the analysis of crystal structure reveal the dimerisation and an altered binding path, which may be responsible for improved affinity and altered selectivity of this newly created starch-binding domain. The functional and structural characterization of CP90 suggests that it has significant potential in industrial applications.

Comparative analysis for the production of fatty acid alkyl esterase using whole cell biocatalyst and purified enzyme from Rhizopus oryzae on waste cooking oil (sunflower oil)

The petroleum fuel is nearing the line of extinction. Recent research and technology have provided promising outcomes to rely on biodiesel as the alternative and conventional source of fuel. The use of renewable source - vegetable oil constitutes the main stream of research. In this preliminary study, Waste Cooking Oil (WCO) was used as the substrate for biodiesel production. Lipase enzyme producing fungi Rhizopus oryzae 262 and commercially available pure lipase enzyme were used for comparative study in the production of Fatty Acid Alkyl Esters (FAAE). The whole cell (RO 262) and pure lipase enzyme (PE) were immobilized using calcium alginate beads. Calcium alginate was prepared by optimizing with different molar ratios of calcium chloride and different per cent sodium alginate. Entrapment immobilization was done for whole cell biocatalyst (WCB). PE was also immobilized by entrapment for the transesterification reaction. Seven different solvents - methanol, ethanol, n-propanol, n-butanol, iso-propanol, iso-butanol and iso-amyl alcohol were used as the acyl acceptors. The reaction parameters like temperature (30°C), molar ratio (1:3 - oil:solvent), reaction time (24 h), and amount of enzyme (10% mass ratio to oil) were also optimized for methanol alone. The same parameters were adopted for the other acyl acceptors too. Among the different acyl acceptors - methanol, whose reaction parameters were optimized showed maximum conversion of triglycerides to FAAE-94% with PE and 84% with WCB. On the whole, PE showed better catalytic converting ability with all the acyl acceptor compared to WCB. Gas chromatography analysis (GC) was done to determine the fatty acid composition of WCO (sunflower oil) and FAAE production with different acyl acceptors.

A simple and accurate two-step long DNA sequences synthesis strategy to improve heterologous gene expression in pichia

In vitro gene chemical synthesis is a powerful tool to improve the expression of gene in heterologous system. In this study, a two-step gene synthesis strategy that combines an assembly PCR and an overlap extension PCR (AOE) was developed. In this strategy, the chemically synthesized oligonucleotides were assembled into several 200–500 bp fragments with 20–25 bp overlap at each end by assembly PCR, and then an overlap extension PCR was conducted to assemble all these fragments into a full length DNA sequence. Using this method, we de novo designed and optimized the codon of Rhizopus oryzae lipase gene ROL (810 bp) and Aspergillus niger phytase gene phyA (1404 bp). Compared with the original ROL gene and phyA gene, the codon-optimized genes expressed at a significantly higher level in yeasts after methanol induction. We believe this AOE method to be of special interest as it is simple, accurate and has no limitation with respect to the size of the gene to be synthesized. Combined with de novo design, this method allows the rapid synthesis of a gene optimized for expression in the system of choice and production of sufficient biological material for molecular characterization and biotechnological application.

Lipases production by solid-state fermentation: the case of Rhizopus homothallicus in perlite

Lipases are widely used in the industry for different purposes. Although these enzymes are mainly produced by submerged fermentation, lipase production by solid-state fermentation (SSF) has been gaining interest due to the advantages of this type of culture. Major advantages are higher production titers and productivity, less catabolite repression, and use of the dried fermented material as biocatalyst. This chapter describes a traditional methodology to produce fungal (Rhizopus homothallicus) lipases by SSF using perlite as inert support. The use of different devices (glass columns or Erlenmeyer flasks) and type of inoculum (spores or growing mycelium) is considered so that lipase production by SSF could be easily performed in any laboratory.

Heterologous expression systems for lipases: a review

The production of heterologous lipases is one of the most promising strategies to increase the productivity of the bioprocesses and to reduce costs, with the final objective that more industrial lipase applications could be implemented. In this chapter, an overview of the most common microbial expression systems for the overproduction of microbial lipases is presented. Prokaryotic system as Escherichia coli and eukaryotic systems as Saccharomyces cerevisiae and Pichia pastoris are analyzed and compared in terms of productivity, operational, and downstream processing facilities. Finally, an overview of heterologous Candida rugosa and Rhizopus oryzae lipases, two of the most common lipases used in biocatalysis, is presented. In both cases, P. pastoris has been shown as the most promising host system.

Codon optimization, expression and enzymatic comparison of Rhizopus oryzae lipases pro-ROL and m-ROL in Pichia pastoris

Rhizopus oryzae lipase (ROL) is not only a biocatalyst used in a broad range of biotechnological fields, but also a model to investigate the function of intramolecular chaperone in the post-translational processing of lipase. In this study, we cloned and expressed the mature lipase gene (m-ROL) containing the pre-sequence (pro-ROL) of R. oryzae HU3005 in Pichia pastoris GS115 and characterized their enzymatic activities. m-ROL exhibited higher hydrolysis activity towards middle-chain substrates (C10 and C12) at pH 9.0, whereas pro-ROL preferred short-chain substrates (C4) and displayed maximal activity at pH 8.0. Moreover, pro-ROL possessed better thermal stability than m-ROL. This enzymatic discrepancy between m-ROL and p-ROL may be due to the pre-sequence that affects the folding and conformation of the mature lipase domain. To improve the expression level of m-ROL in P. pastoris, overlap extension PCR was conducted to substitute eight less-frequently used codons of m-ROL with frequently used codons. After methanol-induced expression for 72 h, the activity and protein content of the codon optimized m-ROL reached 132.7 U/mL and 50.4 mg/L, while the activity of the parental m-ROL and pro-ROL are 28.7 U/mL and 14.4 mg/L, 29.6 U/mL and 14.1 mg/L, respectively.

Production of phytase under solid-state fermentation using Rhizopus oryzae: novel strain improvement approach and studies on purification and characterization

Present study introduces linseed oil cake as a novel substrate for phytase production by Rhizopus oryzae. Statistical approach was employed to optimize various medium components under solid state fermentation (SSF). An overall 8.41-fold increase in phytase production was achieved at the optimum concentrations (w/w, mannitol, 2.05%; ammonium sulfate, 2.84% and phosphate, 0.38%). Further enhancement by 59% was observed due to a novel strain improvement approach. Purified phytase (∼34 kDa) showed optimal temperature of 45 °C, dual pH optima at 1.5 and 5.5 and possesses high catalytic efficiency (2.38×10(6) M(-1) s(-1)). Characterization study demonstrates the phytase as highly thermostable and resistant to proteolysis, heavy metal ions, etc. Furthermore, an improved HPLC method was introduced to confirm the ability of phytase to degrade phytic acid completely and was found to be an efficient method.

Purification and characterization of a novel extracellular tripeptidyl peptidase from Rhizopus oligosporus

A novel extracellular tripeptidyl peptidase (TPP) was homogenously purified from the culture supernatant of Rhizopus oligosporus by sequential fast protein liquid chromatography. The purified enzyme was a 136.5 kDa dimer composed of identical subunits. The effects of inhibitors and metal ions indicated that TPP is a metallo- and serine protease. TPP was activated by divalent cations, such as Co(2+) and Mn(2+), and completely inhibited by Cu(2+). Enzyme activity was optimal at pH 7.0 and 45 °C with a specific activity of 281.9 units/mg for the substrate Ala-Ala-Phe-pNA. The purified enzyme catalyzed cleavage of various synthetic tripeptides but not when proline occupied the P1 position. Purified TPP cleaved the pentapeptide Ala-Ala-Phe-Tyr-Tyr and tripeptide Ala-Ala-Phe, confirming the TPP activity of the enzyme.

Production of cyanophycin in Rhizopus oryzae through the expression of a cyanophycin synthetase encoding gene

Cyanophycin or cyanophycin granule peptide is a protein that results from non-ribosomal protein synthesis in microorganisms such as cyanobacteria. The amino acids in cyanophycin can be used as a feedstock in the production of a wide range of chemicals such as acrylonitrile, polyacrylic acid, 1,4-butanediamine, and urea. In this study, an auxotrophic mutant (Rhizopus oryzae M16) of the filamentous fungus R. oryzae 99-880 was selected to express cyanophycin synthetase encoding genes. These genes originated from Synechocystis sp. strain PCC6803, Anabaena sp. strain PCC7120, and a codon optimized version of latter gene. The genes were under control of the pyruvate decarboxylase promoter and terminator elements of R. oryzae. Transformants were generated by the biolistic transformation method. In only two transformants both expressing the cyanophycin synthetase encoding gene from Synechocystis sp. strain PCC6803 was a specific enzyme activity detected of 1.5 mU/mg protein. In one of these transformants was both water-soluble and insoluble cyanophycin detected. The water-soluble fraction formed the major fraction and accounted for 0.5% of the dry weight. The water-insoluble CGP was produced in trace amounts. The amino acid composition of the water-soluble form was determined and constitutes of equimolar amounts of arginine and aspartic acid.

Expression and characterization of recombinant Rhizopus oryzae lipase for enzymatic biodiesel production

The Rhizopus oryzae lipase containing prosequence was expressed in Pichia pastoris. Recombinant lipase subunit showed a molecular mass of 32 kDa. The maximum activity of recombinant lipase obtained from Mut(s) recombinant was 90 IU/ml. The enzyme was stable in broad ranges of temperatures and pH, with the optimal temperature at 35 °C and pH 7.0. The crude recombinant R. oryzae lipase can be directly used for the transesterification of plant oils at high-water content of 60-100% (w/w) based on oil weight. The addition of 80% water to the transesterification systems resulted in the yield of methyl ester of 95%, 94% and 92% after 72 h using soybean oil, Jatropha curcas seed raw oil and Pistacia chinensis seed raw oil as raw material, respectively. These results indicate that the recombinant lipase is an effective biocatalyst for enzymatic biodiesel production.

[Investigation of permolecular structure of lipase from Rhizopus niveus]

It has been shown by classical biophysical and biochemical methods in combination with atomic microscopy that lipase from Rhizopus niveus exists in a water solution as a dimer with a molecular weight of 96 kDa. The rate of splitting of triglycerides by a dimeric molecules is twice that of monomers. The heat stability of the monomeric form of lipase at temperatures of 20-60 degrees C is significantly higher than that of the native molecule.

[Metabolic engineering of wild acid-resistant yeast for L-lactic acid production]

In order to obtain a yeast strain able to produce L-lactic acid under the condition of low pH and high lactate content, one wild acid-resistant yeast strain isolated from natural samples, was found to be able to grow well in YEPD medium (20 g/L glucose, 20 g/L tryptone, 10 g/L yeast extract, adjusted pH 2.5 with lactic acid) without consuming lactic acid. Based on further molecular biological tests, the strain was identified as Candida magnolia. Then, the gene ldhA, encoding a lactate dehydrogenase from Rhizopus oryzae, was cloned into a yeast shuttle vector containing G418 resistance gene. The resultant plasmid pYX212-kanMX-ldhA was introduced into C. magnolia by electroporation method. Subsequently, a recombinant L-lactic acid producing yeast C. magnolia-2 was obtained. The optimum pH of the recombinant yeast is 3.5 for lactic acid production. Moreover, the recombinant strain could grow well and produce lactic acid at pH 2.5. This recombinant yeast strain could be useful for producing L-lactic acid.

Gene cloning, heterologous expression, and characterization of a high maltose-producing α-amylase of Rhizopus oryzae

A putative α-amylase gene, designated as RoAmy, was cloned from Rhizopus oryzae. The deduced amino acid sequence showed the highest (42.8%) similarity to the α-amylase from Trichoderma viride. The RoAmy gene was successfully expressed in Pichia pastoris GS115 under the induction of methanol. The molecular weight of the purified RoAmy determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis was approximately 48 kDa. The optimal pH and temperature were 4-6 and 60 °C, respectively. The enzyme was stable at pH ranges of 4.5-6.5 and temperatures below 50 °C. Purified RoAmy had a K(m) and V(max) of 0.27 mg/ml and 0.068 mg/min, respectively, with a specific activity of 1,123 U/mg on soluble starch. Amylase activity was strongly inhibited by 5 mM Cu(2+) and 5 mM Fe(2+), whereas 5 mM Ca(2+) showed no significant effect. The RoAmy hydrolytic activity was the highest on wheat starch but showed only 55% activity on amylopectin relative to soluble corn starch, while the pullulanase activity was negligible. The main end products of the polysaccharides tested were glucose and maltose. Maltose reached a concentration of 74% (w/w) with potato starch as the substrate. The enzyme had an extremely high affinity (K(m) = 0.22 mM) to maltotriose. A high ratio of glucose/maltose of 1:4 was obtained when maltotriose was used at an initial concentration of 40 mM.

Biodiesel production by a mixture of Candida rugosa and Rhizopus oryzae lipases using a supercritical carbon dioxide process

In this study, various factors, such as temperature, pressure, agitation speed, water content, and the concentration and ratio of immobilized ROL and CRL were investigated for the efficient enzymatic production of biodiesel using a supercritical carbon dioxide process. Furthermore, a stepwise reaction method for the maintenance of immobilized lipase activity was optimized. Optimal conditions for biodiesel production were determined to be as follows: 130 bar pressure, 45 °C temperature, 250 rpm agitation speed, 10% water content, and 20% immobilized ROL and CRL (1:1). When batch process was performed under optimal conditions, the biodiesel conversion yield was 99.13% at 3 h. Biodiesel conversion yield was 99.99% at 2 h when 90 mmol methanol was used in a stepwise reaction. Moreover, the conversion yield of biodiesel produced by the repeated recycling of immobilized lipase in the stepwise reactions was 85% after 20 reuses.

Acid phosphatase production by Rhizopus delemar: a role played in the Ni(II) bioaccumulation process

The microbial growth and activity of acid phosphatase enzyme during the growth of Rhizopus delemar in the presence or absence of Ni(II) ions were investigated. An increase in initial Ni(II) ion concentration inhibited both growth rate of R. delemar and acid phosphatase activity. The maximum-intrinsic specific growth rate (μ(m)) and Monod constant (K(s)) of microorganism in Ni(II)-free medium were found as 0.0649 h(-1) and 1.8928 g/L, respectively. The inhibition of Ni(II) ions on growth rate of R. delemar was found to be a competitive inhibition and the inhibition constant was found to be 67.11 mg Ni(II)/L. The intrinsic Michaelis-Menten constant (K(m)) and maximum forward velocity of the reaction (v(m)) were determined as 3.17 mM and 833.3 μmol/L min, respectively, in Ni(II)-free medium. In the presence of Ni(II) ions, the activity of acid phosphatase was inhibited. Addition of Ni(II) ions decreased the maximum reaction velocity, v(m), showed noncompetitive-type inhibition kinetics and the inhibition constant was determined as 50mg Ni(II)/L. Maximum Ni(II) uptake was obtained by the growing cells of R. delemar, while the uptake capacity of resting cells was lowest. This study proved that acid phosphatase enzyme participated in the Ni(II) bioaccumulation mechanism of growing R. delemar.

[Xylanase of the micromycete Rhizopus var. microsporus 595: preparation, structural and functional characteristics, and application]

Procedures for the production of endo-1,4-beta-xylanase have been developed. An active producer-Rhizopus var. microsporus BKMF-595-has been chosen, and the conditions of surface and submerged cultivation, as well as the composition of the culture medium for this strain, have been optimized to ensure maximum yield of the target enzyme. Activity of xylomicrosporin Px equaled 123 U/g, while the activity of xylomicrosporin Gx equaled 25 U/cm3. Homogeneous enzyme preparations, purified 59.44-fold and 72.6-fold, have been obtained. The dependence of endo-1,4-beta-xylanase catalytic activity on temperature and pH of the reaction medium has been studied. The enzyme has been shown to be most stable in the pH range 5.0-6.0 and to be thermostable. Amino acid composition and subunit structure of the enzyme were determined; the molecular masses of the subunits equaled 50 and 56 kDa. Carboxyl groups of glutamic and aspartic acid residues of the active center were experimentally shown to play an important role in catalysis. The potential of this enzyme for beer production has been demonstrated.

A newly isolated Rhizopus microsporus var. chinensis capable to secrete amyloltic enzymes with raw-starch-digesting activity

A newly isolated active producer of raw starch digesting amyloltic enzymes, Rhizopus microsporus var. chinensis CICIM-CU F0088 was screened and identified by morphological characteristics and molecular phylogenetic analysis. This fungus was isolated from the soil of Chinese glue pudding mill, and produced high levels of amylolytic activity under solid state fermentation with supplementation of starch and wheat bran. Results of thin layer chromatography showed there are two kinds of amyloltic enzymes formed by this strain, including one alpha-amylase and two glucoamylases. It was found that the two glucoamylases can digest raw corn starch in the electron microscope experiments, and has an optimal temperature of 70 degrees Celsius. These results signified that amyloltic enzymes secreted by strain of Rhizopus microsporus var. chinensis CICIM-CU F0088 were kinds of thermostable amyloltic enzymes and able to digest raw corn starch.

Effect of a buffer mixture system on the activity of lipases during immobilization process

In this study, the effects of various buffers and ionic strengths on the immobilization of Candida rugosa and Rhizopus oryzae lipases were investigated to enhance the activities of the immobilized lipases. Among the various buffers, the optimal buffers and ionic strength for the immobilization of C. rugosa and R. oryzae lipases were determined to be a mixture of 0.25M MOPs and sodium phosphate buffer (pH 6.5). Moreover, the activities of immobilized C. rugosa and R. oryzae lipases under their optimal conditions were 3756.11 and 2845.21U/g matrix, respectively. Furthermore, the activity of immobilized lipases increased by approximately 4.13 and 3.1 times after 24h, respectively. Finally, the activities of the immobilized lipases were maintained at levels greater than 90% of their original activities after ten reuses and at levels greater than 60% of their original activities after twenty reuses.