Construction of a Rhizopus arrhizus glucoamylase gene suitable for expression in distinct host: introns spliced artificially by PCR

Glucoamylase is an industrially extremely important enzyme in the fermentative production of ethanol, used in the enzymatic conversion of starch into high glucose and fructose syrups. The aim of this study is to construct a Rhizopus arrhizus glucoamylase gene (RaGA)-introns artificially spliced by PCR-suitable for expression in S. cerevisiae host and tried expressing in Picha pastoris. In previous work, we failed in amplifying glucoamylase gene from R. arrhizus by RT-PCR, so several primers were designed to splicing the introns by PCR in vitro. Sequence analysis shown that all introns in the RaGA were deleted correctly and no mutant was induced in the extrons compared with the RaGA gene originally cloned. The RaGA gene artificially constructed was transferred into P. pastoris integrative expression vectors pPIC9 (containing small a, Cyrillic-factor). Consequently, the plasmids pPIC9-RaGA was lineared by SacI and inserted into P. pastoris GS115 (His-) genome downstream of the 5'AOX1 promoter by the method of electroporation. Induction by 0.75% methanol for 72 h led to synthesis of secreted glucoamylase. So it is demonstrated that the glucoamylase gene has been expressed in and secreted from P. pastoris.

Native and modified lactate dehydrogenase expression in a fumaric acid producing isolate Rhizopus oryzae 99-880

Rhizopus oryzae is subdivided into two groups based on genetic and phenotypic differences. Type-I isolates accumulate primarily lactic acid when grown in the presence of a fermentable carbon source and contain two lactate dehydrogenase genes, ldhA and ldhB. Type-II isolates synthesize predominantly fumaric acid and only have an ldhB gene. In this study, we determined that ldhB transcript is only minimally expressed in the Type-II isolate R. oryzae 99-880. LdhB enzyme purified from gene clones isolated from the Type-I isolate R. oryzae NRRL 395 and the Type-II isolate R. oryzae 99-880 each showed reductive LDH activity (pyruvate to lactate), while no oxidative LDH activity (lactate to pyruvate) was detected in either preparation. A transformation system was then developed for the first time with R. oryzae 99-880, using a uracil auxotrophic isolate that could be complemented with an orotate phosphoribosyltransferase gene, pyrF, isolated in this study. Transformation of this Type-II isolate with the ldhA gene from R. oryzae NRRL 395 resulted in reductive LDH activity between 1.0 and 1.8 U/mg total protein. Additionally, transformed isolates grown with glucose accumulated up to 27 g lactic acid/l with a concurrent decrease in fumaric acid, ethanol, and glycerol compared with the untransformed and vector-transformed control strains.

Isolation and Characterization of Two Genes That Encode Active Glucoamylase Without a Starch Binding Domain from Rhizopus oryzae

Glucoamylase obtained from Rhizopus sp. is frequently preferred for certain applications of starch modification or saccharification. The predominant enzyme, which contains a starch-binding domain on the amino terminus, has been previously characterized from several species. Additionally, the cDNA encoding this protein was cloned and found to show 100% identity to a R. oryzae strain 99-880 that has recently been sequenced by the Broad Institute of Harvard and Massachusetts Institute of Technology. Analysis of this genome indicates coding regions for two additional glucoamylase genes, amyC and amyD, lacking a starch-binding domain. The two genes encode proteins that are approximately 50% identical to the catalytic region of the AmyA protein and 67% identical to each other. The predicted AmyC and AmyD proteins contain the highly conserved signature sequences of Family 15 glycoside hydrolases. The two genes appear to be transcriptionally expressed in cultures grown in fermentable and gluconeogenic carbon sources. The predicted 49.7-kD AmyC and 48.8-kD AmyD proteins were expressed in several different ways using Pichia pastoris. When the sequence for putative secretion signal was left intact, glucoamylase activity was detected in the crude cell extracts, but no activity was present in the growth medium. However, replacement of this region with the yeast alpha-secretion signal resulted in secretion of active glucoamylase that was able to degrade soluble starch.

Production of a Rhizopus oryzae lipase from Pichia pastoris using alternative operational strategies

Different cultivation strategies have been compared for the production of Rhizopus oryzae lipase (ROL) from Pichia pastoris. Several drawbacks have been found using a methanol non-limited fed-batch. On the one hand, oxygen limitation appeared at early cell dry weights and, on the other hand, high cell death was observed. A temperature limited fed-batch has been proposed to solve both problems. However, in our case study a methanol non-limited fed-batch results in better productivities. Finally, a lower salt medium were used to overcome cell death problems and a temperature limited fed-batch was applied thereafter to solve oxygen transfer limitations. This combined strategy has resulted in lower productivities when compared to a methanol non-limited fed-batch. However the culture could be longer prolonged and a 1.3-fold purer final product was obtained mainly due to cell death reduction.

[Cloning and expression of a new glucoamylase gene]

According to the reported gene sequence of Rhizopus oryzae glucoamylases, the glucoamylase gene containing four introns was cloned from the total DNA of the natural Rhizopus arrhizu. Specific primers were designed to delete introns by overlapping PCR and a new cDNA sequence of Rhizopus arrhizu glucoamylase was obtained. The accession number in gene bank is DQ903853. This gene is successfully expressed in the Picha pastoris, producing a new protein with a high activity of glucoamylase.

Enzymatic deinking of laser printed office waste papers: some governing parameters on deinking efficiency

The protocol for the enzymatic deinking of laser printed waste papers on a laboratory scale using cellulase (C) and hemicellulase (H) of Aspergillus niger (Amano) was developed as an effective method for paper recycling. A maximum deinking efficiency of almost 73% by the enzyme combination of C:H was obtained using the deinking conditions of pulping consistency of 1.0% (w/v) with the pulping time of 1.0min, temperature of 50 degrees C, pH=3.5, agitation rate of 60rpm, pulp concentration of 4% (w/v), concentration of each enzyme of 2.5U/g air dried pulp and the enzyme ratio of 1:1. The deinking efficiency was further enhanced to 95% using the optimized flotation system consisting of pH=6.0, Tween 80 of concentration 0.5% (w/w), working air flow rate of 10.0L/min and temperature of 45 degrees C. The deinked papers were found to exhibit properties comparable to the commercial papers suggesting the effectiveness of the enzymatic process developed.

Evidence of native starch degradation with human small intestinal maltase-glucoamylase (recombinant)

Action of human small intestinal brush border carbohydrate digesting enzymes is thought to involve only final hydrolysis reactions of oligosaccharides to monosaccharides. In vitro starch digestibility assays use fungal amyloglucosidase to provide this function. In this study, recombinant N-terminal subunit enzyme of human small intestinal maltase-glucoamylase (rhMGAM-N) was used to explore digestion of native starches from different botanical sources. The susceptibilities to enzyme hydrolysis varied among the starches. The rate and extent of hydrolysis of amylomaize-5 and amylomaize-7 into glucose were greater than for other starches. Such was not observed with fungal amyloglucosidase or pancreatic alpha-amylase. The degradation of native starch granules showed a surface furrowed pattern in random, radial, or tree-like arrangements that differed substantially from the erosion patterns of amyloglucosidase or alpha-amylase. The evidence of raw starch granule degradation with rhMGAM-N indicates that pancreatic alpha-amylase hydrolysis is not a requirement for native starch digestion in the human small intestine.

Characterization of an extracellular subtilisin protease of Rhizopus microsporus and evidence for its expression during invasive rhinoorbital mycosis

An endoprotease Arp (alkaline Rhizopus protease) was identified and purified to virtual homogeneity from the culture supernatant of an isolate of Rhizopus microsporus var. rhizopodiformis recovered from a non-fatal case of rhinoorbital mucormycosis. N-terminal sequencing of the mature native enzyme was obtained for the first 20 amino acids and revealed high homology to serine proteases of the subtilisin subfamily. Arp migrated in SDS-PAGE with an estimated molecular mass of 33 kDa and had a pI determined to be at pH 8.8. Arp is proteolytically active against various substrates, including elastin, over a broad pH range between 6 and 12 with an optimum at pH 10.5. After invasive mucormycosis, specific antibodies against Arp were detected in stored serum samples taken from the patient from whom the R. microsporus strain of this study had been isolated. Furthermore, in search of factors involved in thrombosis as a typical complication of mucormycosis, a procoagulatory effect of the enzyme has recently been shown. Altogether, these data substantiate the expression of Arp during human rhinoorbital mucormycosis and suggest a role of the enzyme in pathogenesis.

Stable and continuous long-term enzymatic reaction using an enzyme–nanofiber composite

This study shows the preparation and application of enzyme-nanofiber composites for long-term stable operation. The enzyme-nanofiber composite was prepared by coating an enzyme aggregate, the esterase from Rhizopus oryzae, on the surface of the nanofibers. After immobilization on the nanofiber, the apparent K ( m ) for the immobilized esterase was 1.48-fold higher than that of the free esterase, with values of 0.98 and 1.35 mM for the free and immobilized enzymes, respectively. It was found that enzyme-nanofiber was very stable, even when the fibers were shaken in glass vials, preserving 80% of the initial activity for 100 days. In addition, the enzyme-nanofiber composite was used repeatedly in 30 cycles of substrate hydrolysis and still remained active. Consequently, the esterase-nanofiber composite was employed within a continuous reactor system to evaluate its use in a long-term and stable continuous substrate hydrolysis reaction. It was found that the production of p-nitrophenol was stable for at least 400 h. This study demonstrates that the enzyme-nanofiber composite can be used in both repeated-batch mode and a continuous mode for a long-term stable operation.

Solution structure of family 21 carbohydrate-binding module from Rhizopus oryzae glucoamylase

CBMs (carbohydrate-binding modules) function independently to assist carbohydrate-active enzymes. Family 21 CBMs contain approx. 100 amino acid residues, and some members have starchbinding functions or glycogen-binding activities. We report here the first structure of a family 21 CBM from the SBD (starch-binding domain) of Rhizopus oryzae glucoamylase (RoCBM21) determined by NMR spectroscopy. This CBM has a beta-sandwich fold with an immunoglobulin-like structure. Ligand-binding properties of RoCBM21 were analysed by chemical-shift perturbations and automated docking. Structural comparisons with previously reported SBDs revealed two types of topologies, namely type I and type II, with CBM20, CBM25, CBM26 and CBM41 showing type I topology, with CBM21 and CBM34 showing type II topology. According to the chemical-shift perturbations, RoCBM21 contains two ligand-binding sites. Residues in site II are similar to those found in the family 20 CBM from Aspergillus niger glucoamylase (AnCBM20). Site I, however, is embedded in a region with unique sequence motifs only found in some members of CBM21s. Additionally, docking of beta-cyclodextrin and malto-oligosaccharides highlights that side chains of Y83 and W47 (one-letter amino acid code) form the central part of the conserved binding platform in the SBD. The structure of RoCBM21 provides the first direct evidence of the structural features and the basis for protein-carbohydrate recognition from an SBD of CBM21.

Optimization of lipase pretreatment prior to lipase immobilization to prevent loss of activity

In our previous work, a method of pretreating lipase was developed to prevent loss of its activity during covalent immobilization. In this study, Rhizopus oryzae lipase was pretreated before immobilization and then immobilized on a silica gel surface. The effects of the various materials and conditions used in the pretreatment stage on the activity of immobilized lipase were investigated. Immobilized lipase pretreated with 0.1% of soybean oil had better activity than those pretreated with other materials. The optimal temperature, agitation speed, and pretreating time for lipase pretreatment were determined to be 40 degrees C, 200 rpm, and 45 min, respectively. The activity of immobilized soybean oil pretreated lipase was 630 U/g matrix, which is 20 times higher than that of immobilized non-pretreated lipase. In addition, immobilized lipase activity was maintained at levels exceeding 90% of its original activity after 10 reuses.

Construction of a novel synergistic system for production and recovery of secreted recombinant proteins by the cell surface engineering

We determined whether the cocultivation of yeast cells displaying a ZZ-domain and secreting an Fc fusion protein can be a novel tool for the recovery of secreted recombinant proteins. The ZZ-domain from Staphylococcus aureus protein A was displayed on the cell surface of Saccharomyces cerevisiae under the control of the GAL1 promoter. Strain S. cerevisiae BY4742 cells displaying the ZZ-domain on their surface were used for cocultivation with cells that produce a target protein fused to the Fc fragment as an affinity tag. The enhanced green fluorescent protein or Rhizopus oryzae lipase was genetically fused to the N and C termini of the Fc fragment of human immunoglobulin G, respectively. Through analysis by fluorescence-activated cell sorting and enzymatic assay, it was demonstrated that these fusion proteins are successfully produced in the medium and recovered by affinity binding with the cell surface displaying the ZZ-domain. These results suggest that the ZZ-domain-displaying cell and Fc fusion protein-secreting cell can be applied to use in synergistic process of production and recovery of secreted recombinant proteins.

Development of an oat-based biorefinery for the production of L(+)-lactic acid by Rhizopus oryzae and various value-added coproducts

A novel oat-based biorefinery producing L(+)-lactic acid and various value-added coproducts (e.g., beta-glucan, anti-irritant solution) is proposed. Pearling is employed for sequential separation of bran-rich fractions for the extraction of value-added coproducts. Lactic acid production is achieved via fungal fermentation of Rhizopus oryzae on pearled oat flour. Maximum lactic acid concentration (51.7 g/L) and starch conversion yield (0.68 g/g) were achieved when an oat flour concentration of 116.5 g/L was used. Oxygen transfer played a significant role with respect to lactic acid production and starch conversion yield. Rhizopus oryzae produced a range of enzymes (glucoamylase, protease, phosphatase) for the hydrolysis of cereal flour macromolecules. Enzyme production during fungal fermentation has been reported. The proposed biorefining strategy could lead to significant operating cost reduction as compared to current industrial practices for lactic acid production from pure glucose achieved by bacterial fermentations.

Sorbitol co-feeding reduces metabolic burden caused by the overexpression of a Rhizopus oryzae lipase in Pichia pastoris

To improve the specific production rate of Rhizopus oryzae lipase (ROL) in Pichia pastoris, a protein that triggers the unfolded protein response in P. pastoris, the effect of sorbitol/methanol mixed substrates was tested in batch and fed-batch cultures. Remarkably, a different substrate consumption behaviour was observed depending on the host's phenotype (Mut(+) or Mut(s)) in batch cultures: when the methanol assimilation capacity is genetically reduced (Mut(s) phenotype), both substrates were consumed simultaneously, allowing not only a higher specific growth rate but also higher lipase levels (8.7-fold) compared to those obtained by cells growing on methanol as a sole carbon source in batch culture. This effect was not observed in Mut(+) phenotype, where the two substrates were consumed sequentially and the levels of heterologous product were only slightly higher (1.7-fold). A mixed substrate strategy was also applied to a Mut(s) fed-batch culture at a low methanol concentration set-point (0.5 gl(-1)). This resulted in a 2.2-fold increase in the heterologous protein level achieved, compared with the methanol-only feeding strategy. In addition, sorbitol co-feeding permitted the achievement of higher specific growth rates, and avoided the drastic decrease of the specific production rate observed after the start of the induction phase when methanol was used as sole carbon source This resulted in a significant increase in the overall bioprocess volumetric productivity (2.2-fold) and specific productivity (1.7-fold). Moreover, whereas increased ROL gene dosage in Mut(s) strains have been previously reported to be deleterious for P. pastoris cells growing on methanol, sorbitol co-feeding allowed for sustained cell growth and lipase production.

Effect of nonionic surfactants on Rhizopus homothallicus lipase activity

Based on amino-terminal sequencing and mass spectrometry data on the Rhizopus homothallicus lipase extracted using solid (SSF) and submerged state fermentation (SmF) methods, we previously established that the two enzymes were identical. Differences were observed, however, in terms of the specific activity of these lipases and their inhibition by diethyl p-nitrophenyl phosphate (E600). The specific activity of the SSF lipase (10,700 mumol/min/mg) was found to be 1.2-fold that of SmF lipase (8600 mumol/min/mg). These differences might be the result of residual Triton X-100 molecules interacting with the SSF lipase. To check this hypothesis, the SmF lipase was incubated with submicellar concentrations of Triton X-100. The specific activity of the lipase increased after this treatment, reaching similar values to those measured with the SSF lipase. Preincubating SSF and SmF lipases with E600 at a molar excess of 100 for 1 h resulted in 80% and 60% enzyme inhibition levels, respectively. When the SmF lipase was preincubated with Triton X-100 for 1 h at a concentration 100 times lower than the Triton X-100 critical micellar concentration, the inhibition of the lipase by E600 increased from 60% to 80%. These results suggest that residual detergent monomers interacting with the enzyme may affect the kinetic properties of the Rh. homothallicus lipase.

[Cloning and expression of a delta6-fatty acid desaturase gene from Rhizopus stolonifer in Saccharomyces cervisiae]

Fatty acid composition of fungi is analysed through the gas chromatography( GC) technique. With specific activity a novel enzyme delta6-fatty acid desaturase was screened and isolated from Rhizopus stolonifer. In this study R. stolonifer was identified as a fungal species that produced plentiful gamma-linolenic acid. A 1475bp full-length cDNA, designated as RnD6D here, with high homology to fungal delta6-fatty acid desaturase genes was isolated from R. stolonifer using reverse transcription polymerase chain reaction and rapid amplification of cDNA ends methods. Sequence analysis indicated that this cDNA sequence had an open reading frame of 1380bp encoding a deduced polypeptide of 459 amino acids. Bioinformatics analysis characterized the putative RnD6D protein as a typical membrane-bound desaturase, including three conserved histidine-rich motifs, hydropathy profile and a cytochrome b5-like domain in the N-terminus. To elucidate the function of this novel putative desaturase, the coding sequence was expressed in Saccharomyces cerevisiae strain INVScl. A novel peak corresponding to gamma-linolenic acid(GLA) methyl ester standards was detected with the same retention time, which was absent in the cell transformed with empty vector. The percentage of this new GLA was 12.25% of total fatty acids. The result demonstrated that the coding produced delta6-fatty acid desaturase activity of RnD6D which led to the accumulation of gamma-linolenic acid.

Preparation of a whole-cell biocatalyst of mutated Candida antarctica lipase B (mCALB) by a yeast molecular display system and its practical properties

To prepare a whole-cell biocatalyst of a stable lipase at a low price, mutated Candida antarctica lipase B (mCALB) constructed on the basis of the primary sequences of CALBs from C. antarctica CBS 6678 strain and from C. antarctica LF 058 strain was displayed on a yeast cell surface by alpha-agglutinin as the anchor protein for easy handling and stability of the enzyme. When mCALB was displayed on the yeast cell surface, it showed a preference for short chain fatty acids, an advantage for producing flavors; although when Rhizopus oryzae lipase (ROL) was displayed, the substrate specificity was for middle chain lengths. When the thermal stability of mCALB on the cell surface was compared with that of ROL on a cell surface, T (1/2), the temperature required to give a residual activity of 50% for heat treatment of 30 min, was 60 degrees C for mCALB and 44 degrees C for ROL indicating that mCALB displayed on cell surface has a higher thermal stability. Furthermore, the activity of the displayed mCALB against p-nitrophenyl butyrate was 25-fold higher than that of soluble CALB, as reported previously. These findings suggest that mCALB-displaying yeast is more practical for industrial use as the whole-cell biocatalyst.

Synthetic activity enhancement of membrane-bound lipase from Rhizopus chinensis by pretreatment with isooctane

The cell-bound lipase from Rhizopus chinensis CCTCC M201021 with high catalysis ability for ester synthesis was located as a membrane-bound lipase by the treatments of Yatalase firstly. In order to improve its synthetic activity in non-aqueous phase, the pretreatments of this enzyme with various organic solvents were investigated. The pretreatment with isooctane improved evidently the lipase synthetic activity, resulting in about 139% in relative synthetic activity and 115% in activity recovery. The morphological changes of mycelia caused by organic solvent pretreatments could influence the exposure of the membrane-bound enzyme from mycelia and the exhibition of the lipase activity. The pretreatment conditions with isooctane and acetone were further investigated, and the optimum effect was obtained by the isooctane pretreatment at 4 degrees C for 1 h, resulting in 156% in relative synthetic activity and 126% in activity recovery. When the pretreated lipases were employed as catalysts for the esterification production of ethyl hexanoate in heptane, higher initial reaction rate and higher final molar conversion were obtained using the lipase pretreated with isooctane, compared with the untreated lyophilized one. This result suggested that the pretreatment of the membrane-bound lipase with isooctane could be an effective method to substitute the lyophilization for preparing biocatalysts used in non-aqueous phase reactions.

Amyloglucosidase-catalyzed synthesis of eugenyl and curcuminyl glycosides

Glycosylation of the phenolic hydroxyl group of the phenyl propanoid systems, eugenol 1 and curcumin 2, using an amyloglucosidase from Rhizopus and a beta-glucosidase from sweet almonds together with carbohydrates (D-glucose 3, D-mannose 4, maltose 5, sucrose 6 and D-mannitol 7) in di-isopropyl ether produced glycosides at 7-52% yields in 72 h. Spectral studies indicated that the reaction occurred between the phenolic OH groups and C-1 and/or 6-O-groups of the carbohydrates with curcumin exhibiting bis glycosylation.

A simple model-based control for Pichia pastoris allows a more efficient heterologous protein production bioprocess

A predictive control algorithm coupled with a PI feedback controller has been satisfactorily implemented in the heterologous Rhizopus oryzae lipase production by Pichia pastoris methanol utilization slow (Mut(s)) phenotype. This control algorithm has allowed the study of the effect of methanol concentration, ranging from 0.5 to 1.75 g/L, on heterologous protein production. The maximal lipolytic activity (490 UA/mL), specific yield (11,236 UA/g(biomass)), productivity (4,901 UA/L . h), and specific productivity (112 UA/g(biomass)h were reached for a methanol concentration of 1 g/L. These parameters are almost double than those obtained with a manual control at a similar methanol set-point. The study of the specific growth, consumption, and production rates showed different patterns for these rates depending on the methanol concentration set-point. Results obtained have shown the need of implementing a robust control scheme when reproducible quality and productivity are sought. It has been demonstrated that the model-based control proposed here is a very efficient, robust, and easy-to-implement strategy from an industrial application point of view.

Biochemical and molecular characterization of a lipase produced by Rhizopus oryzae

A novel strain of Rhizopus oryzae WPG secretes a noninduced lipase (ROLw) in the culture medium; purified ROLw is a protein of 29 kDa, the 45 N-terminal amino acid residues were sequenced, this sequence is very homologous to Rhizopus delemar lipase (RDL), Rhizopus niveus lipase (RNL) and R. oryzae lipase (ROL29) sequences; the cloning and sequencing of the part of the gene encoding the mature ROLw, shows two nucleotides differences with RDL, RNL and ROL29 sequences corresponding to the change of the residues 134 and 200; ROLw does not present the interfacial activation phenomenon when using tripropionin or vinyl propionate as substrates; the lipase activity is maximal at pH 8 and at 37 degrees C, specific activities of 3500 or 900 U mg(-1) were measured at 37 degrees C and at pH 8, using olive oil emulsion or tributyrin as substrates, respectively; ROLw is unable to hydrolyse triacylglycerols in the presence of high concentration of bile salts; it is a serine enzyme as it is inhibited by tetrahydrolipstatin and was stable between pH 5 and pH 8.

Enzymatic conversion of waste cooking oils into alternative fuel--biodiesel

Production of biodiesel from pure oils through chemical conversion may not be applicable to waste oils/fats. Therefore, enzymatic conversion using immobilized lipase based on Rhizopus orzyae is considered in this article. This article studies this technological process, focusing on optimization of several process parameters, including the molar ratio of methanol to waste oils, biocatalyst load, and adding method, reaction temperature, and water content. The results indicate that methanol/oils ratio of 4, immobilized lipase/oils of 30 wt% and 40 degrees C are suitable for waste oils under 1 atm. The irreversible inactivation of the lipase is presumed and a stepwise addition of methanol to reduce inactivation of immobilized lipases is proposed. Under the optimum conditions the yield of methyl esters is around 88-90%.

Enhancement of Activity of Lipase-Displaying Yeast Cells and Their Application to Optical Resolution of (R,S)-1-Benzyloxy-3-Chloro-2-Propyl Monosuccinate

Rhizopus oryzae lipase (ROL) was displayed on the cell surface of Saccharomyces cerevisiae via the Flo1 N-terminal region (1100 amino acids), which corresponds to a flocculation functional domain. The activity of lipase-displaying yeast whole-cell biocatalysts was enhanced 7.3-fold by incubation of the yeast cells at 20 degrees C in distilled water for 8 days after 8 day cultivation. The amount of lipase molecules present in cell wall and intracellular fractions was found to be increased 4.5- and 1.8-fold, respectively, by incubation, which proves that ROL molecules are expressed during incubation. The ROL-displaying yeast whole-cell biocatalyst with enhanced activity was successfully catalyzed by optical resolution of the pharmaceutical precursor (R,S)-1-benzyloxy-3-chloro-2-propyl monosuccinate. Moreover, it showed stable activity through at least eight reaction cycles. These results demonstrate that ROL-displaying yeast cells with enhanced activity by incubation in distilled water are very effective in industrial bioconversion processes.

[Screening of a low alcohol dehydrogenase activity mutant of rhizopus oryzae and the regulation of Zn2+ and Mg2+]

Ethanol is the main by-product in the fermentation broth of Rhizopus oryzae As3.3461 for the production of high-optical purity L-lactic acid. Alcohol Dehydrogenase (ADH) is the branch pathway enzyme that catalyzes the transformation of ethanol from pyruvate in Rhizopus oryzae, which decreases the conversion rate of glucose to L-lactic acid. Thus, screening the mutants with lower ADH activity may increase lactate production dramatically. In present study, Rhizopus oryzae As3.3461 was mutated with N-methyl-N'-nitro-N-nitrosoguanidine (NTG), and 21 mutants which showed lower ADH activity were isolated with selective medium of Yeast-Peptone-Dextrose (YPD) containing 0.6% allyl alcohol (V/V). Compared with other mutants, the 12th mutant strain (named as HBF-12) shows the highest conversion rate of L-lactic acid. By contrast with Rhizopus oryzae As3.3461, the parent strain, the ethanol production and the ADH activity of HBF-12 decrease 73.6% and 76%, respectively. Whereas, the L-lactic acid production and the LDH activity of HBF-12 increase 41.2% and 19.6% than those of the parent strain, respectively. The activities of ADH and LDH of HBF-12 were regulated by Zn2+ and Mg2+, but showed opposite effects. Added with Zn2+ to the concentration of 0.01% improves the ADH activity dramatically, but inhibits the activity of LDH. By contraries, added with Mg2+ improves the LDH activity markedly, but inhibits the ADH activity slightly. In fermentation experiment, the addition of Zn2+ and Mg2+ show different effects on the accumulation of ethanol, L-lactic acid and the biomass in mutant HBF-12. When improve the concentration of Zn2+, the accumulation of L-lactic acid and the biomass show the decreased trend, but the production of ethanol show positive effect. With the improvement of the concentration of Mg2+, the production of lactic acid and biomass increase markedly, but no effect on the production of ethanol. When ferment under the concentrations of Zn2+ 0.01% and Mg2+ 0.04% in fermentation medium, the lactate production of HBF-12 reached the highest level, 96.21 g/L.

Lipase localization in Rhizopus oryzae cells immobilized within biomass support particles for use as whole-cell biocatalysts in biodiesel-fuel production

To identify the lipase responsible for the methanolysis activity of fungus whole-cell biocatalysts, the lipase localization of Rhizopus oryzae cells was determined. Western blot analysis showed that R. oryzae cells produce two types of lipase with different molecular masses of 34 and 31 kDa; the former (ROL34) was bound to the cell wall, whereas the latter (ROL31) was mainly bound to the cell membrane. It was found that cell immobilization within reticulated polyurethane foam biomass support particles strongly inhibits the secretion of membrane-bound lipase into the culture medium. An investigation of the relationship between ROL34 and ROL31 suggested that ROL31 originates from the cleavage of a 28-amino-acid residue at the N-terminus of ROL34. The addition of olive oil to the culture medium led to the retention of increased amounts of lipase within the cell. This phenomenon was further confirmed by an immunofluorescence labeling of hyphal cells. When cells were cultivated with various substrate-related compounds, such as olive oil and oleic acid, the intracellular methanolysis activity strongly correlated with the relative amounts of the membrane-bound lipase, which suggests that ROL31 localized in the membrane plays a crucial role in the methanolysis activity of R. oryzae cells.