Safety evaluation of the food enzyme mucorpepsin from the non-genetically modified Rhizomucor miehei strain LP-N836

The food enzyme mucorpepsin (EC 3.4.23.23) is produced with the non-genetically modified Rhizomucor miehei strain LP-N836 by Meito Sangyo Co., Ltd. The native enzyme can be chemically modified to produce a more thermolabile form. The food enzyme is free from viable cells of the production organism. It is intended to be used in the processing of dairy products for the production of cheese and fermented dairy products. Dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to 0.108 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 95 mg TOS/kg bw per day, the mid-dose tested, which when compared with the estimated dietary exposure, resulted in a margin of exposure of at least 880. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and four matches with respiratory allergens and one with a food allergen (mustard) were found. The Panel considered that the risk of allergic reactions upon dietary exposure to this food enzyme, particularly in individuals sensitised to mustard proteins, cannot be excluded. Based on the data provided, the Panel concluded that both the native and thermolabile forms of this food enzyme do not give rise to safety concerns under the intended conditions of use.

Safety evaluation of the food enzyme mucorpepsin from the non-genetically modified Rhizomucor miehei strain M19-21

The food enzyme mucorpepsin (EC 3.4.23.23) is produced with the non-genetically modified Rhizomucor miehei strain M19-21 by Meito Sangyo Co., Ltd. The enzyme is chemically modified to produce a thermolabile form. The food enzyme was considered free from viable cells of the production organism. It is intended to be used in the processing of dairy products for the production of cheese and fermented dairy products. Based on the maximum use levels, dietary exposure was estimated to be up to 0.108 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 226 mg TOS/kg bw per day, the highest dose tested, which, when compared with the estimated dietary exposure, results in a margin of exposure of at least 2093. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and four matches to respiratory allergens and one match to a food allergen (mustard) were found. The Panel considered that the risk of allergic reactions upon dietary exposure to this food enzyme, particularly in individuals sensitised to mustard proteins, cannot be excluded. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns, under the intended conditions of use.

Safety evaluation of the food enzyme mucorpepsin from the non-genetically modified Rhizomucor miehei strain FRO

The food enzyme mucorpepsin (EC 3.4.23.23) is produced with the non-genetically modified Rhizomucor miehei strain FRO by DSM Food Specialties B.V. The enzyme can be chemically modified to produce a thermolabile form. The food enzyme is free from viable cells of the production organism. It is intended to be used in three food manufacturing processes: processing of dairy products for the production of (1) cheese, (2) edible rennet casein, (3) fermented dairy products. Dietary exposure to the food enzyme-total organic solids (TOS) was estimated to be up to about 0.072 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 2000 mg TOS/kg bw per day, the highest dose tested, which, when compared with the estimated dietary exposure, results in a margin of exposure of at least 27,778. A search for the similarity of the amino acid sequence of the food enzyme to known allergens was made and five matches were found. The Panel considered that a risk of allergic reactions upon dietary exposure to this food enzyme cannot be excluded, but is considered low, except for individuals sensitised to mustard proteins, for whom the risk will not exceed that of mustard consumption. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

Safety evaluation of the food enzyme mucorpepsin from Rhizomucor miehei strain DSM 29547

The food enzyme mucorpepsin (EC 3.4.23.23) is produced with the non‐genetically modified Rhizomucor miehei strain DSM 29547 by Chr. Hansen. The food enzyme is free from viable cells of the production organism. It is intended to be used in dairy processing for cheese production. The dietary exposure to the food enzyme–total organic solids (TOS) was estimated to be up to 0.26 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not indicate a safety concern. The systemic toxicity was assessed by a repeated dose 90‐day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 618 mg TOS/kg bw per day, the highest dose tested, which when compared with the estimated dietary exposure, results in a margin of exposure of at least 2,400. A search for similarity of the amino acid sequence of the food enzyme to known allergens was made and three matches were found. The Panel considered that, under the intended conditions of use, the risk of allergic sensitisation and elicitation reactions by dietary exposure cannot be excluded but is considered low except for individuals sensitised to mustard proteins, but this risk will not exceed that of mustard consumption. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns, under the intended conditions of use.

Optimization of protease production from Rhizomucor miehei Rm4 isolate under solid-state fermentation

BACKGROUND

Protease is one of the most important industrial enzymes. The importance of protease bioproduction comes from meeting the increasing demand for this enzyme especially in the cheese industry. Rhizomucor miehei protease is the preferred substitute for the traditional rennet. Solid-state fermentation (SSF) shows promising results in enzyme production. An optimization strategy was applied to optimize the production of Rhizomucor miehei protease in a solid medium. The components of the fermentation medium were screened by using the one-factor-at-a-time (OFAT) approach. The optimization process then was performed by using the response surface methodology (RSM) approach based on five factors (fermentation time, temperature, pH, moisture content, nitrogen concentration) at five levels. Specific milk clotting activity and milk clotting activity/proteolytic activity ratio were considered as response variables in the optimization process.

RESULTS

Among several combinations, wheat bran was selected as the best substrate. Casein was selected based on preliminary screening of nitrogen sources. The optimal conditions identified by RSM analysis were found to be 81.21 h, 41.11°C, 6.31, 80%, and 1.33% for fermentation time, temperature, pH, moisture content, and casein concentration, respectively. The performed fermentation process under the optimized conditions gave an enzymatic extract with the values of 5.11 mg/mL, 2258.13 Soxhlet unit/mL, 441.90 Soxhlet unit/mg, 1.14 protease unit/mg, and 388.66 for protein content, milk clotting activity, specific clotting activity, specific proteolytic activity, and milk clotting activity/proteolytic activity ratio, respectively. The aforementioned values were close to the predicted values.

CONCLUSION

The high milk clotting activity and the relatively low proteolytic activity signify higher specificity of the produced enzyme, which is favorable in cheese making. The observed results reveal the efficiency of the applied statistical approaches in obtaining desired values of response variables and minimizing experimental runs, as well as achieving good predictions for response variables.

Design of an innovative technique for application of the immobilized Rhizomucor miehei (CBS: 370.65) rennin-like enzyme on paraffin wax in cheese-making process and the kinetic properties of the immobilized enzyme

This research aimed to invent a new method for cheese making using Rennin-like enzyme from fungus with high efficiency and reusability. Accordingly, Rhizomucor miehei (CBS: 370.65) showed a promising milk clotting (MCF) activity and the mycotoxin test was negative. The partially purified enzyme was immobilized by entrapment in paraffin wax using different techniques. Wax-enzyme tablets preparation exhibited complete immobilization yield (100%). Ca²⁺ had a marked stimulating effect on the activities of both the free and immobilized enzyme forms. The immobilized enzyme (MCI) exhibited more than sixteen effective reuses to produce cheese in a batch reactor. The free and the immobilized forms recorded their optimum activities at pH 5.6 and 55 °C, respectively. The immobilization process reduced the consumed activation energy (E_a) to 39%. The immobilized enzyme was more stable than the free form. Among all the used substrates, buffalo milk and full cream milk showed the highest immobilized enzyme activity (7142.9 U). km value was unaffected by the immobilization process and was 600 mg reaction^-1, for both. Schematic setup was used as semi-pilot example for a repeated batch of MCI wax tablets. This design solved the clotting problem completely by the refine bundle nominated its agreeability in the cheese-making process.

Case Report: Metagenomics Next-Generation Sequencing for Diagnosing Cerebral Infarction and Infection Caused by Hematogenous Disseminated Mucormycosis in a Patient With Acute Lymphoblastic Leukemia

Disseminated mucormycosis, a serious complication, is associated with high mortality in patients with acute leukemia after chemotherapy. Blood cultures are always negative because of recurrent empirical antifungal treatments. The identification of pathogens is important for diagnosis and therapy. In this case report, we diagnosed culture-negative disseminated mucormycosis with Rhizomucor miehei infection leading to cerebral infarction in a patient with leukemia using metagenomics next-generation sequencing (mNGS) form peripheral blood, cerebral spinal fluid, and bronchoalveolar lavage fluid. mNGS technology can be applied to precisely diagnose culture-negative disseminated mucormycosis.

Characterization of a Novel Aspartic Protease from Rhizomucor miehei Expressed in Aspergillus niger and Its Application in Production of ACE-Inhibitory Peptides

Rhizomucor miehei is an important fungus that produces aspartic proteases suitable for cheese processing. In this study, a novel aspartic protease gene (RmproB) was cloned from R. miehei CAU432 and expressed in Aspergillus niger. The amino acid sequence of RmproB shared the highest identity of 58.2% with the saccharopepsin PEP4 from Saccharomyces cerevisiae. High protease activity of 1242.2 U/mL was obtained through high density fermentation in 5 L fermentor. RmproB showed the optimal activity at pH 2.5 and 40 °C, respectively. It was stable within pH 1.5-6.5 and up to 45 °C. RmproB exhibited broad substrate specificity and had K_m values of 3.16, 5.88, 5.43, and 1.56 mg/mL for casein, hemoglobin, myoglobin, and bovine serum albumin, respectively. RmproB also showed remarkable milk-clotting activity of 3894.1 SU/mg and identified the cleavage of Lys21-Ile22, Leu32-Ser33, Lys63-Pro64, Leu79-Ser80, Phe105-Met106, and Asp148-Ser149 bonds in κ-casein. Moreover, duck hemoglobin was hydrolyzed by RmproB to prepare angiotensin-I-converting enzyme (ACE) inhibitory peptides with high ACE-inhibitory activity (IC₅₀ of 0.195 mg/mL). The duck hemoglobin peptides were further produced at kilo-scale with a yield of 62.5%. High-level expression and favorable biochemical characterization of RmproB make it a promising candidate for cheese processing and production of ACE-inhibitory peptides.

Crystal structure of a chitinase (RmChiA) from the thermophilic fungus Rhizomucor miehei with a real active site tunnel

A chitinase gene (RmChiA) encoding 445 amino acid (aa) residues from a fungus Rhizomucor miehei was cloned and overexpressed in Escherichia coli. Two kinds of RmChiA crystal forms, with space groups P3₂ 2 1 and P1, were obtained by sitting-drop vapor diffusion and the structures were determined by X-ray diffraction. The overall structure of RmChiA monomer, which is the first structure of bacterial-type chitinases from nonpathogenic fungi, adopts a canonical triosephosphate isomerase (TIM) barrel fold with two protruding chitinase insertion domains. RmChiA exhibited a unique NxDxE catalytical motif and a real active site tunnel structure, which are firstly found in GH family 18 chitinases. The motif had high structural homolog with the typical DxDxE motif in other GH family 18 chitinases. The tunnel is formed by two unusual long loops, containing 15 aa and 45 aa respectively, linked by a disulfide bond across the substrate-binding cleft. Mutation experiments found that opening the roof of tunnel structure increased the hydrolysis efficiency of RmChiA, but the thermostability of the mutants decreased. Moreover, the tunnel structure endowed RmChiA with the exo-chitinase character.

Recombinant Protein Production and Purification Using Eukaryotic Cell Factories

Cloning proteins enables their production and characterization for further studies. This requires inserting the gene of the studied protein to be inserted in a vector, which then will be transformed to the host cell used as "factory." Consequently, the "biomass" of host cells will be produced using bioreactors. Here we describe the production of Rhizomucor miehei lipase (RML) by cloning the corresponding genes in the yeast Pichia pastoris. This enzyme is used as a biocatalyst for biofuel production. The successfully produced recombinant proteins are then purified using ion exchange chromatography.

First case of fatal Rhizomucor miehei endocarditis in an immunocompromised patient

Rhizomucor miehei is a cause of bovine mycotic abortion and mastitis and has rarely been described in human disease. Here, we report the first isolation of R. miehei from native mitral valve tissue in a fatal case of endocarditis that substantiates its pathogenic potential. Apart from morphological criteria, molecular methods were a cornerstone for definite diagnosis.

Biodegradation of slop oil by endophytic Bacillus cereus EN18 coupled with lipase from Rhizomucor miehei (Palatase®)

Removal of slop oil, a by-product of oil refining, also obtained in cleaning up of oil tanks and filters is a difficult issue. High content of hydrocarbons (C3-C40) and other organic compounds makes this waste difficult to eliminate from the environment. The purpose of this investigation was to combine bacterial degradation by endophytic Bacillus cereus EN18 with biotransformation performed using lipase enzyme preparation (Palatase®) to remove recalcitrant compounds present in slop oil from the environment. Endophytic B. cereus EN18 was able to biodegrade up to 40% of slop oil while supplementation with lipase improved the efficiency of contamination removal in about one third. Also the use of lipase enzyme preparation resulted in higher microbial activity of B. cereus EN18 bacterial strain, as well as higher concentration of fatty acids in the culture medium, which indicates higher degradation efficiency. Obtained results suggest that lipase preparation from Rhizomucor miehei (Palatase®) may be a useful agent to improve microbial degradation of recalcitrant pollutants, like slop oil in water environments. GC and spectrometric analysis revealed that hydrocarbons from slop oil were effectively degraded while using both microbial degradation and lipase catalysis.

Osmolytes and membrane lipids in adaptive response of thermophilic fungus Rhizomucor miehei to cold, osmotic and oxidative shocks

In contrast to mesophiles, in which levels of trehalose and phosphatidic acids (PA) increased only under heat shock (HS), in thermophiles trehalose and PA were predominant under optimal growth conditions. To study the role of trehalose protection in the adaptation of thermophiles to various stressors, the composition of osmolytes and membrane lipids in the thermophilic fungus Rhizomucor miehei was studied under cold (CS), osmotic (OS) and oxidative (OxS) shocks. CS resulted in no accumulation of glycerol in the mycelium, while the amount of trehalose decreased. The main lipid changes were the increase in the PA proportion with simultaneous decrease of sterols (St), the increase of the unsaturation degree of polar lipids and the decrease of the ergosterol proportion in total St. OS did not cause changes in the lipid composition, but led to the decrease of ergosterol proportion too. Despite the low ability of Mucorales to produce polyols, increase in the level of arabitol and glycerol was observed under OS. OxS led to the decrease of trehalose level and had no effect on the lipid composition. Thus, our results show the similarity (OS) and the difference (CS and OxS) between adaptation mechanisms of thermophiles and mesophiles.

A novel high maltose-forming α-amylase from Rhizomucor miehei and its application in the food industry

A novel α-amylase gene (RmAmyA) from Rhizomucor miehei was cloned and expressed in Pichia pastoris. RmAmyA showed 70% amino acid identity with the α-amylase from Rhizomucor pusillus. A high α-amylase activity of 29,794.2 U/mL was found through high cell density fermentation. The molecular mass of RmAmyA was determined to be 49.9 kDa via SDS-PAGE. RmAmyA was optimally active at 75 °C and pH 6.0, and it did not require Ca²⁺ to improve its activity. It exhibited broad substrate specificity towards amylose, amylopectin, soluble starch, pullulan, and cyclodextrins. High level of maltose (54%, w/w) was produced after liquefied starch was hydrolysed with RmAmyA for 16 h. Moreover, the addition of RmAmyA into Chinese steamed bread resulted in 7.7% increment in the specific volume, and 17.2% and 11.5% reduction in the chewiness and hardness, respectively. These results indicate that RmAmyA might be a potential candidate for applications in the food industry.

Effect of blends of camel chymosin and microbial rennet (Rhizomucor miehei) on chemical composition, proteolysis and residual coagulant activity in Iranian Ultrafiltered White cheese

Iranian Ultrafiltered White cheese was produced by using different blends of coagulants (100:0, 75:25, 50:50, 25:75 and 0:100; Rhizomucor miehei and camel chymosin, respectively) and ripened for 90 days. The effect of different combinations of these coagulants on chemical composition, proteolysis and residual coagulant activity of the cheeses were studied. The results showed that pH, fat-in-dry matter, salt-in-dry matter and protein contents of the cheeses were significantly influenced by type and concentration of the coagulants. The difference between proteolytic activities of the two coagulants resulted in different levels of proteolysis in the cheeses. A direct relationship was determined between using higher concentrations of R. miehei and increasing the hydrolysis of α_s1-casein in the cheeses, during ripening. The residual coagulant activity was influenced by the type and concentration of the coagulant as well. In conclusion, R. miehei provided a higher level of proteolysis and residual coagulant activity compared with camel chymosin.

Solid-State Fermentation as an Economic Production Method of Lipases

Solid-state fermentation (SSF) has been largely employed during the last three decades to produce different biomolecules of industrial interest, particularly enzymes. Through the use of agroindustrial wastes as SSF substrates, an economic process of lipases production can be achieved. In this chapter we describe a comprehensive SSF method for producing an economical preparation of Rhizomucor miehei lipase, employing sugarcane bagasse and used vegetal oil as substrates. To demonstrate the usefulness of the lipase produced by this method, we utilized directly the dried fermented solid, as a heterogeneous biocatalyst for the ethanolysis of different fats and oils. Final ethyl ester conversions (>90%, 24 h) were similar with those obtained using a commercial immobilized Rhizomucor miehei lipase at our best conditions. In this work we demonstrated that SSF is an easy and economical method for the production of lipases that can be used directly as heterogeneous biocatalysts for biodiesel production, employing low-cost feedstocks.

A novel aspartic protease from Rhizomucor miehei expressed in Pichia pastoris and its application on meat tenderization and preparation of turtle peptides

A novel aspartic protease gene (RmproA) was cloned from the thermophilic fungus Rhizomucor miehei CAU432 and expressed in Pichia pastoris. The RmproA was successfully expressed in P. pastoris as an active extracellular protease. High protease activity of 3480.4 U/mL was obtained by high cell-density fermentation. The protease was purified by the two step protocols to homogeneity. The molecular mass of the RmproA was estimated to be 52.4 kDa by SDS-PAGE and 50.6 kDa by gel filtration. The purified enzyme was optimally active at pH 5.5 and 55 °C, respectively. The enzyme exhibited a broad range of substrate specificity. RmproA-treated pork muscle showed lower shear force than papain-treated sample at a relative low concentration, suggesting its effectiveness on meat tenderization. Moreover, turtle hydrolysis by RmproA resulted in a large amount of small peptides, which exhibited high ACE-inhibitory activity. Thus, RmproA may be a potential candidate for several industrial applications.

Study the influence of culture conditions on rennin production by Rhizomucor miehei using solid-state fermentations

Investigations were conducted on the production of Rennin enzyme from the fungi Rhizomucor miehei 3420 NRRL using Solid-State fermentation. Wheat bran was used as a substrate. The influence of moisture content, incubation temperature, and the initial pH of fermentation medium were studied. The protein content, milk clotting activity (MCA), specific activity, proteolytic activity (PA), and (MCA/PA) ratio of the extracted enzyme were calculated after 4 days of incubation to evaluate the quality of the enzyme. The results showed that the optimal conditions for production were as follows: incubation temperature of 40 °C, moisture content of 60%, and pH of (3). Under these conditions, a production process of Rennin enzyme was established, and the values of protein content, milk clotting activity, specific activity, proteolytic activity, and (MCA/PA) ratio reached to 4 mg/mL, 600 SU/mL, 150 SU/mg, 45 PU/mL, 13.3 respectively.

Directed evolution of a β-mannanase from Rhizomucor miehei to improve catalytic activity in acidic and thermophilic conditions

BACKGROUND

β-Mannanase randomly cleaves the β-1,4-linked mannan backbone of hemicellulose, which plays the most important role in the enzymatic degradation of mannan. Although the industrial applications of β-mannanase have tremendously expanded in recent years, the wild-type β-mannanases are still defective for some industries. The glycoside hydrolase (GH) family 5 β-mannanase (RmMan5A) from Rhizomucor miehei shows many outstanding properties, such as high specific activity and hydrolysis property. However, owing to the low catalytic activity in acidic and thermophilic conditions, the application of RmMan5A to the biorefinery of mannan biomasses is severely limited.

RESULTS

To overcome the limitation, RmMan5A was successfully engineered by directed evolution. Through two rounds of screening, a mutated β-mannanase (mRmMan5A) with high catalytic activity in acidic and thermophilic conditions was obtained, and then characterized. The mutant displayed maximal activity at pH 4.5 and 65 °C, corresponding to acidic shift of 2.5 units in optimal pH and increase by 10 °C in optimal temperature. The catalytic efficiencies (k_cat/K_m) of mRmMan5A towards many mannan substrates were enhanced more than threefold in acidic and thermophilic conditions. Meanwhile, the high specific activity and excellent hydrolysis property of RmMan5A were inherited by the mutant mRmMan5A after directed evolution. According to the result of sequence analysis, three amino acid residues were substituted in mRmMan5A, namely Tyr233His, Lys264Met, and Asn343Ser. To identify the function of each substitution, four site-directed mutations (Tyr233His, Lys264Met, Asn343Ser, and Tyr233His/Lys264Met) were subsequently generated, and the substitutions at Tyr233 and Lys264 were found to be the main reason for the changes of mRmMan5A.

CONCLUSIONS

Through directed evolution of RmMan5A, two key amino acid residues that controlled its catalytic efficiency under acidic and thermophilic conditions were identified. Information about the structure-function relationship of GH family 5 β-mannanase was acquired, which could be used for modifying β-mannanases to enhance the feasibility in industrial application, especially in biorefinery process. This is the first report on a β-mannanase from zygomycete engineered by directed evolution.

Biochemical Characterization of a Novel Acidic Exochitinase from Rhizomucor miehei with Antifungal Activity

A novel chitinase gene (RmChi44) from Rhizomucor miehei was cloned and expressed in Escherichia coli as an intracellular soluble and active protein. The recombinant chitinase (RmChi44) was purified to homogeneity and biochemically characterized. The molecular mass of RmChi44 was estimated to be 44.6 kDa on SDS-PAGE. RmChi44 displayed an acidic pH optimum of 4.5 and was stable within pH 4.5-9.0. The optimal temperature of RmChi44 was found to be 50 °C. The Km values of RmChi44 for colloidal chitin and glycol chitin were 4.02 and 1.55 mg/mL, respectively. RmChi44 hydrolyzed colloidal chitin to yield mainly N-acetyl chitobiose, exhibiting an exotype cleavage pattern. Moreover, the enzyme displayed β-N-acetylglucosaminidase activity, splitting N-acetyl COSs with degree of polymerization (DP) 2-5 into their monomer. In addition, RmChi44 showed antifungal activity against some phytopathogenic fungi. This is the first report on an exochitinase showing β-N-acetylglucosaminidase activity and antifungal activity from Rhizomucor species.

Crystal structure and characterization of a novel L-serine ammonia-lyase from Rhizomucor miehei

L-serine ammonia-lyase, as a member of the β-family of pyridoxal-5'-phosphate (PLP) dependent enzymes, catalyzes the conversion of L-serine (L-threonine) to pyruvate (α-ketobutyrate) and ammonia. The crystal structure of L-serine ammonia-lyase from Rhizomucor miehei (RmSDH) was solved at 1.76 Å resolution by X-ray diffraction method. The overall structure of RmSDH had the characteristic β-family PLP dependent enzyme fold. It consisted of two distinct domains, both of which show the typical open twisted α/β structure. A PLP cofactor was located in the crevice between the two domains, which was attached to Lys52 by a Schiff-base linkage. Unique residue substitutions (Gly78, Pro79, Ser146, Ser147 and Thr312) were discovered at the catalytic site of RmSDH by comparison of structures of RmSDH and other reported eukaryotic L-serine ammonia-lyases. Optimal pH and temperature of the purified RmSDH were 7.5 and 40 °C, respectively. It was stable in the pH range of 7.0-9.0 and at temperatures below 40 °C. This is the first crystal structure of a fungal L-serine ammonia-lyase. It will be useful to study the catalytic mechanism of β-elimination enzymes and will provide a basis for further enzyme engineering.

Biotransformation of oleanolic and maslinic methyl esters by Rhizomucor miehei CECT 2749

The pentacyclic triterpenoids methyl oleanolate, methyl maslinate, methyl 3β-hydroxyolean-9(11),12-dien-28-oate, and methyl 2α,3β-dihydroxy-12β,13β-epoxyolean-28-oate were biotransformed by Rhizomucor miehei CECT 2749. Microbial transformation of methyl oleanolate produced only a 7β,30-dihydroxylated metabolite with a conjugated 9(11),12-diene system in the C ring. Biotransformation of the substrate with this 9(11),12-diene system gave the same 7β,30-dihydroxylated compound together with a 7β,15α,30-trihydroxyl derivative. The action of this fungus (R. miehei) on methyl maslinate was more varied, isolating metabolites with a 30-hydroxyl group, a 9(11),12-diene system, an 11-oxo group, or an 12-oxo group. Microbial transformation of the substrate with a 12β,13β-epoxy function resulted in the isolation of two metabolites with 12-oxo and 28,13β-olide groups, hydroxylated or not at C-7β, together with a 30-hydroxy-12-oxo derivative. The structures of these derivatives were deduced by extensive and rigorous spectroscopic studies.

The first crystal structure of a glycoside hydrolase family 17 β-1,3-glucanosyltransferase displays a unique catalytic cleft

β-1,3-Glucanosyltransferase (EC 2.4.1.-) plays an important role in the formation of branched glucans, as well as in cell-wall assembly and rearrangement in fungi and yeasts. The crystal structures of a novel glycoside hydrolase (GH) family 17 β-1,3-glucanosyltransferase from Rhizomucor miehei (RmBgt17A) and the complexes of its active-site mutant (E189A) with two substrates were solved at resolutions of 1.30, 2.30 and 2.27 Å, respectively. The overall structure of RmBgt17A had the characteristic (β/α)8 TIM-barrel fold. The structures of RmBgt17A and other GH family 17 members were compared: it was found that a conserved subdomain located in the region near helix α6 and part of the catalytic cleft in other GH family 17 members was absent in RmBgt17A. Instead, four amino-acid residues exposed to the surface of the enzyme (Tyr135, Tyr136, Glu158 and His172) were found in the reducing terminus of subsite +2 of RmBgt17A, hindering access to the catalytic cleft. This distinct region of RmBgt17A makes its catalytic cleft shorter than those of other reported GH family 17 enzymes. The complex structures also illustrated that RmBgt17A can only provide subsites -3 to +2. This structural evidence provides a clear explanation of the catalytic mode of RmBgt17A, in which laminaribiose is released from the reducing end of linear β-1,3-glucan and the remaining glucan is transferred to the end of another β-1,3-glucan acceptor. The first crystal structure of a GH family 17 β-1,3-glucanosyltransferase may be useful in studies of the catalytic mechanism of GH family 17 proteins, and provides a basis for further enzymatic engineering or antifungal drug screening.

Biochemical Characterization of a Novel Endo-1,5-α-l-arabinanase from Rhizomucor miehei

A novel gene (designated as RmArase) encoding endo-1,5-α-l-arabinanase from a thermophilic fungus Rhizomucor miehei was cloned and expressed in Escherichia coli. The gene had an open reading frame (ORF) of 930 base pairs (bp) encoding 309 amino acids. The amino acid sequence shared highest identity (56%) with a glycoside hydrolase (GH) family 43 endo-1,5-α-l-arabinase from Bacillus subtilis and low identity (35%) with the endo-1,5-α-l-arabinase from Aspergillus niger. The recombinant endo-1,5-α-l-arabinase (RmArase) was purified to homogeneity with a molecular mass of 40.6 kDa. The purified enzyme had a specific activity of 109 units/mg. The optimal temperature and pH of RmArase were determined to be 55 °C and 5.5, respectively. It was stable up to 45 °C and within pH 5.0-8.5. The K_m values of RmArase toward debranched arabinan and sugar beet arabinan were 5.8 and 27.5 mg/mL, respectively. RmArase efficiently degraded arabinans to yield and arabinobiose and arabinose as major end products, which was different from most other endo-1,5-α-l-arabinases. The synergistic action of RmArase and the pectinase could significantly improve the degradation of sugar beet pulp. These properties make RmArase useful in several industries.

Expression and characterization of a novel β-glucosidase, with transglycosylation and exo-β-1,3-glucanase activities, from Rhizomucor miehei

A novel β-glucosidase gene, designated RmBglu3B, was cloned from the thermophilic fungus, Rhizomucor miehei CAU432. Its 2196-bp open reading frame encoded 731 amino acids. Its deduced amino-acid sequence showed highest identity (66%) with a glycoside hydrolase family 3 β-glucosidase from R. miehei NRRL5382. RmBglu3B was successfully expressed in Escherichia coli. The recombinant enzyme was purified to homogeneity with 18.2-fold purification and 59% recovery yield. Molecular masses of 76.5 kDa, by SDS-PAGE, and 66.4 kDa, by gel filtration, suggested that it is a monomer. Optimal pH and temperature of the purified enzyme were 5.0 and 50°C, respectively. RmBglu3B exhibited a broad range of substrate specificity, catalyzing the cleavage of β-1,2, β-1,3, β-1,4 and β-1,6 linkages, in various oligosaccharides, to liberate glucose. RmBglu3B also showed relatively high activity (19.1 U/mg) toward laminaran and transglycosylation activity, enabling gentiobiose production. This enzyme is a potential candidate for several industrial applications.

High-level production of β-1,3-1,4-glucanase by Rhizomucor miehei under solid-state fermentation and its potential application in the brewing industry

AIMS

To improve the β-1,3-1,4-glucanase production by Rhizomucor miehei under solid-state fermentation (SSF) for industrial application.

METHODS AND RESULTS

The fermentation conditions for β-1,3-1,4-glucanase production by R. miehei CAU432 under SSF were optimized using a 'one-factor-at-a-time' method. Under the optimized fermentation conditions, viz. oatmeal (0·45-0·9 mm) as sole carbon source, 5% (w/w) peptone as sole nitrogen source, initial moisture of 80% (w/w), initial culture pH of 5·0, incubation temperature of 50°C and incubation time of 6 days, the highest β-1,3-1,4-glucanase activity of 20,025 U g(-1) dry substrate was achieved, which represents the highest yield for β-1,3-1,4-glucanase production ever reported. The crude enzyme was extracted and purified to homogeneity with a purification fold of 4·6 and a recovery yield of 9·0%. The addition of the purified β-1,3-1,4-glucanase in mash obviously reduced its filtration time (24·6%) and viscosity (2·61%).

CONCLUSIONS

The optimal fermentation conditions for maximal β-1,3-1,4-glucanase production under SSF was obtained, and the enzyme was suitable for application in the malting process.

SIGNIFICANCE AND IMPACT OF THE STUDY

The high production yield and excellent capability of the enzyme may enable it great potential in industries, especially in brewing industry.

Improved production of a recombinant Rhizomucor miehei lipase expressed in Pichia pastoris and its application for conversion of microalgae oil to biodiesel

BACKGROUND

We previously cloned a 1,3-specific lipase gene from the fungus Rhizomucor miehei and expressed it in methylotrophic yeast Pichia pastoris strain GS115. The enzyme produced (termed RML) was able to catalyze methanolysis of soybean oil and showed strong position specificity. However, the enzyme activity and amount of enzyme produced were not adequate for industrial application. Our goal in the present study was to improve the enzyme properties of RML in order to apply it for the conversion of microalgae oil to biofuel.

RESULTS

Several new expression plasmids were constructed by adding the propeptide of the target gene, optimizing the signal peptide, and varying the number of target gene copies. Each plasmid was transformed separately into P. pastoris strain X-33. Screening by flask culture showed maximal (21.4-fold increased) enzyme activity for the recombinant strain with two copies of the target gene; the enzyme was termed Lipase GH2. The expressed protein with the propeptide (pRML) was a stable glycosylated protein, because of glycosylation sites in the propeptide. Quantitative real-time RT-PCR analysis revealed two major reasons for the increase in enzyme activity: (1) the modified recombinant expression system gave an increased transcription level of the target gene (rml), and (2) the enzyme was suitable for expression in host cells without causing endoplasmic reticulum (ER) stress. The modified enzyme had improved thermostability and methanol or ethanol tolerance, and was applicable directly as free lipase (fermentation supernatant) in the catalytic esterification and transesterification reaction. After reaction for 24 hours at 30°C, the conversion rate of microalgae oil to biofuel was above 90%.

CONCLUSIONS

Our experimental results show that signal peptide optimization in the expression plasmid, addition of the gene propeptide, and proper gene dosage significantly increased RML expression level and enhanced the enzymatic properties. The target enzyme was the major component of fermentation supernatant and was stable for over six months at 4°C. The modified free lipase is potentially applicable for industrial-scale conversion of microalgae oil to biodiesel.

Biotransformation of oleanolic and maslinic acids by Rhizomucor miehei

Microbial transformation of oleanolic acid by Rhizomucor miehei produced three metabolites. A known compound, a 30-hydroxyl derivative (queretaroic acid), and two 7β,30- and 1β,30-dihydroxylated metabolites, respectively. The action of the same fungus (R. miehei) on maslinic acid produced an olean-11-en-28,13β-olide derivative, a metabolite hydroxylated at C-30, an 11-oxo derivative, and two metabolites with an 11α,12α-epoxy group, hydroxylated or not at C-30. Their structures were elucidated by extensive analyses of their spectroscopic data, and also by chemical correlations.

The structure of a glycoside hydrolase family 81 endo-β-1,3-glucanase

Endo-β-1,3-glucanases catalyze the hydrolysis of β-1,3-glycosidic linkages in glucans. They are also responsible for rather diverse physiological functions such as carbon utilization, cell-wall organization and pathogen defence. Glycoside hydrolase (GH) family 81 mainly consists of β-1,3-glucanases from fungi, higher plants and bacteria. A novel GH family 81 β-1,3-glucanase gene (RmLam81A) from Rhizomucor miehei was expressed in Escherichia coli. Purified RmLam81A was crystallized and the structure was determined in two crystal forms (form I-free and form II-Se) at 2.3 and 2.0 Å resolution, respectively. Here, the crystal structure of a member of GH family 81 is reported for the first time. The structure of RmLam81A is greatly different from all endo-β-1,3-glucanase structures available in the Protein Data Bank. The overall structure of the RmLam81A monomer consists of an N-terminal β-sandwich domain, a C-terminal (α/α)6 domain and an additional domain between them. Glu553 and Glu557 are proposed to serve as the proton donor and basic catalyst, respectively, in a single-displacement mechanism. In addition, Tyr386, Tyr482 and Ser554 possibly contribute to both the position or the ionization state of the basic catalyst Glu557. The first crystal structure of a GH family 81 member will be helpful in the study of the GH family 81 proteins and endo-β-1,3-glucanases.

High yield of wax ester synthesized from cetyl alcohol and octanoic acid by lipozyme RMIM and Novozym 435

Wax esters are long-chain esters that have been widely applied in premium lubricants, parting agents, antifoaming agents and cosmetics. In this study, the biocatalytic preparation of a specific wax ester, cetyl octanoate, is performed in n-hexane using two commercial immobilized lipases, i.e., Lipozyme^® RMIM (Rhizomucor miehei) and Novozym^® 435 (Candida antarctica). Response surface methodology (RSM) and 5-level-4-factor central composite rotatable design (CCRD) are employed to evaluate the effects of reaction time (1–5 h), reaction temperature (45–65 °C), substrate molar ratio (1–3:1), and enzyme amount (10%–50%) on the yield of cetyl octanoate. Using RSM to optimize the reaction, the maximum yields reached 94% and 98% using Lipozyme^® RMIM and Novozym^® 435, respectively. The optimum conditions for synthesis of cetyl octanoate by both lipases are established and compared. Novozym^® 435 proves to be a more efficient biocatalyst than Lipozyme^® RMIM.