A Whole-Process Visible Strategy for the Preparation of Rhizomucor miehei Lipase with Escherichia coli Secretion Expression System and the Immobilization.

BACKGROUND: Rhizomucor miehei (RM) lipase is a regioselective lipase widely used in food, pharmaceutical and biofuel industries. However, the high cost and low purity of the commercial RM lipase limit its industrial applications. Therefore, it is necessary to develop cost-effective strategies for large-scale preparation of this lipase. The present study explored the high-level expression of RM lipase using superfolder green fluorescent protein (sfGFP)-mediated Escherichia coli secretion system. RESULTS: The sfGFP(-15) mutant was fused to the C-terminus of RM lipase to mediate its secretion expression. The yield of the fusion protein reached approximately 5.1 g/L with high-density fermentation in 5-L fermentors. Unlike conventional secretion expression methods, only a small portion of the target protein was secreted into the cell culture while majority of the fusion protein was still remained in the cytoplasm. However, in contrast to intracellular expression, the target protein in the cytoplasm could be transported efficiently to the supernatant through a simple washing step with equal volume of phosphate saline (PBS), without causing cell disruption. Hence, the approach facilitated the downstream purification step of the recombinant RM lipase. Moreover, contamination or decline of the engineered strain and degradation or deactivation of the target enzyme can be detected efficiently because they exhibited bright green fluorescence. Next, the target protein was immobilized with anion-exchange and macropore resins. Diethylaminoethyl sepharose (DEAE), a weak-basic anion-exchange resin, exhibited the highest bind capacity but inhibited the activity of RM lipase dramatically. On the contrary, RM lipase fixed with macropore resin D101 demonstrated the highest specific activity. Although immobilization with D101 didn't improve the activity of the enzyme, the thermostability of the immobilized enzyme elevated significantly. The immobilized RM lipase retained approximately 90% of its activity after 3-h incubation at 80 °C. Therefore, D101 was chosen as the supporting material of the target protein. CONCLUSION: The present study established a highly efficient strategy for large-scale preparation of RM lipase. This innovative technique not only provides high-purity RM lipase at a low cost but also has great potential as a platform for the preparation of lipases in the future.

In silico and in vitro safety assessment of a fungal biomass from Rhizomucor pusillus for use as a novel food ingredient.

To address the growing world population and reduce the impact of environmental changes on the global food supply, ingredients are being produced using microorganisms to yield sustainable and innovative products. Food ingredients manufactured using modern biotechnology must be produced by non-toxigenic and nonpathogenic production organisms that do not harbor antimicrobial resistance (AMR). Several fungal species represent attractive targets as sources of alternative food products. One such product is a fungal biomass obtained from the fermentation of Rhizomucor pusillus strain CBS 143028. The whole genome sequence of this strain was annotated and subjected to sequence homology searches and in silico phenotype prediction tools to identify genetic elements encoding for protein toxins active via oral consumption, virulence factors associated with pathogenicity, and determinants of AMR. The in silico investigation revealed no genetic elements sharing significant sequence homology with putative virulence factors, protein toxins, or AMR determinants, including the absence of mucoricin, an essential toxin in the pathogenesis of mucormycosis. These in silico findings were corroborated in vitro based on the absence of clinically relevant mycotoxin or antibacterial secondary metabolites. Consequently, it is unlikely that R. pusillis strain CBS 143028 would pose a safety concern for use in food for human consumption.

N-glycosylation as an effective strategy to enhance characteristics of Rhizomucor miehei lipase for biodiesel production.

The construction of methanol-resistant lipases with high catalytic activity is world-shattering for biodiesel production. A semi-rational method has been constructed to enhance the properties of Rhizomucor miehei lipase with propeptide (ProRML) by introducing N-glycosylation sites in the Loop structure. The enzyme activities of the mutants N288 (1448.89 ± 68.64 U/mg) and N142 (1073.68 ± 33.87 U/mg) increased to 56.09 and 41.56 times relative to that of wild type ProRML (WT, 25.83 ± 0.73 U/mg), respectively. After incubation in 50 % methanol for 2.5 h, the residual activities of N314 and N174-1 were 95 % and 85%, which were higher than the WT (27 %). Additionally, the biodiesel yield of all mutants was increased after a one-time addition of methanol for 24 h. Among them, N288 increased the quantity of biodiesel from colza oil from 9.49 % to 88 %, and N314 increased the amount of biodiesel from waste soybean oil from 8.44% to 70%. This study provides an effective method to enhance the properties of lipase and improve its application potential in biodiesel production.

Effect of Propeptide Mutations on the Directed Evolution of Rhizomucor miehei Lipase.

BACKGROUND: A series of mutants of Rhizomucor miehei lipase (RML) screened through four rounds of directed evolution were studied. Mutants' triglyceride hydrolysis activity was assessed, and their genes were sequenced. Results showed that mutations in the propeptide can improve the activity of RML during evolution. Two parts of propeptide (wild-type and mutant) and mature region were connected by molecular simulation technology. METHODS: The spatial structure of the most positive mutants containing the mutations in the propeptide was mainly characterized by the increase in the opening angle of the lid structure in the mature region of RML, the enhancement of the hydrophobicity of the active center, and the triad of the active center shifted outward. RESULTS: The three indexes above explain the mechanism of propeptide mutations on the activity change of the target protein. In addition, statistical analysis of all the mutants screened in directed evolution showed that: (1) most of the mutants with increased activity contained mutations of the propeptide, (2) in the later stage of directed evolution, the number of active mutants decreased gradually, and the mutations of inactivated protein mainly occurred in the mature region, and (3) in the last round of directed evolution, the mutations distributed in the propeptide improved the mutant activity further. The results showed that the propeptide reduced RML's evolutionary pressure and delayed the emergence of the evolutionary platform. CONCLUSION: These findings reveal the role of propeptide in the evolution of RML and provide strategies for the molecular transformation of other lipases.

Enhanced activity of Rhizomucor miehei lipase by directed saturation mutation of the propeptide.

The propeptide is a short sequence that facilitates protein folding. In this study, four highly active Rhizomucor miehei lipase (RML) mutants were obtained through saturation mutagenesis at three propeptide positions: Ser8, Pro35, and Pro47. The enzyme activities of mutants P35 N, P47 G, P47 N, and S8E/P35S/P47A observed at 40 °C, and pH 8.0 were 10.19, 7.53, 6.15, and 8.24 times of that wild-type RML, respectively. The S8E/P35S/P47A mutant showed good thermostability. After incubation at 40 °C for 1 h, 98.98 % of its initial activity remained, whereas wild-type RML retained only 78.76 %. This result indicated that the enhancement of hydrophilicity of 35- and 47- amino-acid residues could promote the interaction between the propeptide and the mature peptide and the enzyme activity and expression level. Highly conserved sites had a more significant impact on enzyme performance than did other sites, similar to the Pro35 and Pro47 mutants showed in this study. This study provides a new idea for protein modification: enzyme performance can be improved through propeptide regulation.

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.

Crude glycerol impurities improve Rhizomucor miehei lipase production by Pichia pastoris.

Crude glycerol, a by-product of biodiesel production, was employed as the carbon source to produce lipase using Pichia pastoris. Under identical fermentation conditions, cell growth and lipase activity were improved using crude glycerol instead of pure glycerol. The impacts of crude glycerol impurities (methyl ester, grease, glycerol, methanol, and metal ions Na+, Ca2+, and Fe3+) on lipase production were investigated. Impurities accelerated P. pastoris entering the stationary phase. Na+, Ca2+, and grease in waste crude glycerol were the main factors influencing higher lipase activity. Through response surface optimization of Ca2+, Na+, and grease concentrations, lipase activity reached 1437 U/mL (15,977 U/mg), which was 2.5 times that of the control. This study highlights the economical and highly efficient valorization of crude glycerol, demonstrating its possible utilization as a carbon source to produce lipase by P. pastoris without pretreatment.

Efficient improvement of surface displayed lipase from Rhizomucor miehei in PichiaPink™ protease-deficient system.

Lipase from Rhizomucor miehei (RML) is a promising biocatalyst used in food industry, fine chemicals, and biodiesel production. Yeast surface display allows direct application of lipase in form of whole-cell biocatalyst, avoiding purification and immobilization process, but the protease of the host cell may affect the activity of displayed lipase. Herein, we used the protease-deficient Pichia pastoris, PichiaPink™ as host to display RML efficiently. RML gene, GCW21 gene and α-factor gene were co-cloned into plasmid pPink LC/HC and transformed into protease-deficient P. pastoris. After inducution expression for 96 h, the lipase activity of displayed RML reached 121.72 U/g in proteinase-A-deficient P. pastoris harboring high-copy plasmid, which exhibited 46.7% higher than recombinant P. pastoris without protease defect. Displayed RML occurred the maximum activity at pH 8.0 and 45 °C and the optimal substrate was p-nitrophenyl octanoate. Metal ions Li+, Na+, K+, and Mg2+ of 1-10 mM had activation towards displayed RML. Displayed RML was effectively improved in PichiaPink™ protease-deficient system, which may promote the further research and development for the industrial application of RML.

Comparative Analysis of Different Isolated Oleaginous Mucoromycota Fungi for Their γ-Linolenic Acid and Carotenoid Production.

γ-Linolenic acid (GLA) and carotenoids have attracted much interest due to their nutraceutical and pharmaceutical importance. Mucoromycota, typical oleaginous filamentous fungi, are known for their production of valuable essential fatty acids and carotenoids. In the present study, 81 fungal strains were isolated from different Egyptian localities, out of which 11 Mucoromycota were selected for further GLA and carotenoid investigation. Comparative analysis of total lipids by GC of selected isolates showed that GLA content was the highest in Rhizomucor pusillus AUMC 11616.A, Mucor circinelloides AUMC 6696.A, and M. hiemalis AUMC 6031 that represented 0.213, 0.211, and 0.20% of CDW, respectively. Carotenoid analysis of selected isolates by spectrophotometer demonstrated that the highest yield of total carotenoids (640 µg/g) was exhibited by M. hiemalis AUMC 6031 and M. hiemalis AUMC 6695, and these isolates were found to have a similar carotenoid profile with, ß-carotene (65%), zeaxanthin (34%), astaxanthin, and canthaxanthin (5%) of total carotenoids. The total fatty acids of all tested isolates showed moderate antimicrobial activity against Staphylococcus aureus and Salmonella Typhi, and Penicillium chrysogenum. To the best of our knowledge, this is the first report on the highest yield of total lipid accumulation (51.74% CDW) by a new oleaginous fungal isolate R. pusillus AUMC 11616.A. A new scope for a further study on this strain will be established to optimize and improve its total lipids with high GLA production. So, R. pusillus AUMC 11616.A might be a potential candidate for industrial application.

Protein Thermal Stability Engineering Using HoTMuSiC.

The rational design of enzymes is a challenging research field, which plays an important role in the optimization of a wide series of biotechnological processes. Computational approaches allow screening all possible amino acid substitutions in a target protein and to identify a subset likely to have the desired properties. They can thus be used to guide and restrict the huge, time-consuming search in sequence space to reach protein optimality. Here we present HoTMuSiC, a tool that predicts the impact of point mutations on the protein melting temperature, which uses the experimental or modeled protein structure as sole input and is available at the dezyme.com website. Its main advantages include accuracy and speed, which makes it a perfect instrument for thermal stability engineering projects aiming at designing new proteins that feature increased heat resistance or remain active and stable in nonphysiological conditions. We set up a HoTMuSiC-based pipeline, which uses additional information to avoid mutations of functionally important residues, identified as being too well conserved among homologous proteins or too close to annotated functional sites. The efficiency of this pipeline is successfully demonstrated on Rhizomucor miehei lipase.

Overexpression of GRAS Rhizomucor miehei lipase in Yarrowia lipolytica via optimizing promoter, gene dosage and fermentation parameters.

Rhizomucor miehei lipase (RML), a GRAS catalyst with wide applications, was overexpressed in Yarrowia lipolytica, also a GRAS unconventional yeast, via a combined strategy, optimization for promoter, gene dosage and fermentation process. The lipase activity of the recombinant strain was first increased from 19.5 to 26.9 U/mL via codon optimization of rml gene. Subsequently, a method was developed for constructing hybrid promoters harboring different copy number of upstream activation sequences fragment (UAS1B), and the recombinant strain Po1g/hp12d-rml 25# reached 38.9 U/mL. On this basis, expression vectors with different optimized rml gene copy numbers were constructed and introduced into Y. lipolytica Po1g. The recombinant strain Po1g/hp12d-2rml 14# carrying 12 copies of UAS1B in the upstream of pLEUmin and 2 copies of rml gene obtained the highest lipase activity of 59.6 U/mL. Moreover, in optimized shaking flask culture parameters: 5% (m/v) of d-Sorbitol, 2% (v/v) inoculation density, initial pH 7.0, and 30 mL initial culture medium, the RML activity of Po1g/hp12d-2rml 14# further reached 157 U/mL after 84-h of incubation at 28 ℃. Overall, RML activity was enhanced about 8-fold compared with the initial recombinant strain via the combined strategy, which provides a consolidated basis for the large-scale production of RML in Y. lipolytica to match urgent demand of the market.

Efficient expression of a novel thermophilic fungal ß-mannosidase from Lichtheimia ramosa with broad-range pH stability and its synergistic hydrolysis of locust bean gum.

ß-Mannosidase (EC 3.2.1.25) is an exoglycosidase specific for the hydrolysis of terminal ß-1,4-glycosidic linkage in mannan which can be applied in the food manufacture, animal feed, bioethanol making and coffee extraction industries. A novel ß-mannosidase gene (Lrman5A) from Lichtheimia ramosa was synthesized and recombinantly expressed in Pichia pastoris X33. Lrman5A encodes 444 amino acids with a calculated molecular mass of 51.0 kDa which shares the highest identity (73%) with the ß-mannosidase from Rhizomucor miehei. Purified recombinant Lrman5A showed the maximal activity at pH 6.0 and 65°C, had broad-range pH stability (retaining >65% activity after incubation at pH 3.0-8.5 at 37°C for 24 h), and was highly thermostable (retaining >80% activity after incubation at 65°C for 10 min). The specific activity, and Km of Lrman5A was 17.5 U/mg and 1.377 mM, respectively. Lrman5A and GH5 ß-mannanase displayed significant synergistic effects on the degradation of locust bean gum (LBG) and released more mannose (up to 2.89 folds) by simultaneous or sequential addition. Due to its hydrolytic properties, Lrman5A may have potential applications in the area of bioenergy, feed and food processing.

Fatal Pulmonary and Cerebellar Zygomycosis due to Rhizomucor pusillus in a Ringed Seal (Pusa hispida).

A 4-year-old captive ringed seal (Pusa hispida) was treated with subcutaneous antibacterial injections for pus exuding wounds in the skin and associated blubber following a bite attack. Three months after the incident, the animal presented nystagmus and died the following day. At necropsy, there was a 25 × 18 × 25 mm well-delineated, opaque nodular mass in the lung, besides the skin ulcers and localized areas of discoloration in the blubber correlating with the bite wound and injection sites. Histopathology of the pulmonary mass demonstrated severe eosinophilic inflammatory infiltration among numerous intralesional fungal hyphae. The hyphae were irregularly branched, broad and aseptate, consistent of zygomycosis. Magnetic resonance imaging was conducted on the head, which was initially frozen intact, revealing diffuse areas of hyperintensity in the cerebellum. Restricted histopathologic examination of the cerebellum showed severe granulomatous inflammation well spread within the neuroparenchyma, associated with abundant intralesional fungal hyphae similar to those appreciated in the pulmonary mass. Molecular analyses of the fungi in the pulmonary and cerebellar tissue identified the etiologic agent in both sites as Rhizomucor pusillus. The likely route of infection is through inhalation of R. pusillus spores or fragmented hyphae from the environment that developed into an initial pulmonary infection, becoming the source of hematogenous dissemination to the cerebellum. The skin and blubber lesions likely contributed to immunosuppression. Zygomycosis is uncommon in pinnipeds, and the present report emphasizes the importance of considering zygomycete dissemination even when the primary focus is highly confined.

Enhancing the Thermostability of Rhizomucor miehei Lipase with a Limited Screening Library by Rational-Design Point Mutations and Disulfide Bonds.

Rhizomucor miehei lipase (RML), as a kind of eukaryotic protein catalyst, plays an important role in the food, organic chemical, and biofuel industries. However, RML retains its catalytic activity below 50°C, which limits its industrial applications at higher temperatures. Soluble expression of this eukaryotic protein in Escherichia coli not only helps to screen for thermostable mutants quickly but also provides the opportunity to develop rapid and effective ways to enhance the thermal stability of eukaryotic proteins. Therefore, in this study, RML was engineered using multiple computational design methods, followed by filtration via conservation analysis and functional region assessment. We successfully obtained a limited screening library (only 36 candidates) to validate thermostable single point mutants, among which 24 of the candidates showed higher thermostability and 13 point mutations resulted in an apparent melting temperature ([Formula: see text]) of at least 1°C higher. Furthermore, both of the two disulfide bonds predicted from four rational-design algorithms were further introduced and found to stabilize RML. The most stable mutant, with T18K/T22I/E230I/S56C-N63C/V189C-D238C mutations, exhibited a 14.3°C-higher [Formula: see text] and a 12.5-fold increase in half-life at 70°C. The catalytic efficiency of the engineered lipase was 39% higher than that of the wild type. The results demonstrate that rationally designed point mutations and disulfide bonds can effectively reduce the number of screened clones to enhance the thermostability of RML.IMPORTANCER. miehei lipase, whose structure is well established, can be widely applied in diverse chemical processes. Soluble expression of R. miehei lipase in E. coli provides an opportunity to explore efficient methods for enhancing eukaryotic protein thermostability. This study highlights a strategy that combines computational algorithms to predict single point mutations and disulfide bonds in RML without losing catalytic activity. Through this strategy, an RML variant with greatly enhanced thermostability was obtained. This study provides a competitive alternative for wild-type RML in practical applications and further a rapid and effective strategy for thermostability engineering.

Co-expression of lipase isozymes for enhanced expression in Pichia pastoris.

To enhance the overall expression level of lipase isozymes which catalyse the same reaction in Pichia pastoris through co-expression of isozymes from different sources; several types of co-expression ways were constructed to determine the co-expression efficiencies of lipase isozymes in P. pastoris. The results showed that the Kex2-mediated co-expression of lipase isozymes could express Rhizomucor miehei lipase (RML) and Thermomyces lanuginosus lipase (TLL) simultaneously, and GS-RMk-kTL displayed an average lipase activity of 306·91 U ml-1 , higher than GS-RML and GS-kTL (2·89 and 300·59 U ml-1 ) expressed independently in P. pastoris, and the sum of both (303·48 U ml-1 ), implying the potential of isozyme co-expression mediated by Kex2 in increasing the overall recombinant expression, but the low recombinant expression of RML in P. pastoris weakened the overall increasing effect on lipase expression in the isozyme co-expression strains. In addition, the fusion isozymes were successfully expressed, but with low lipase activities. Furthermore, 2A peptide could successfully mediate the co-expression and secretion of lipase isozymes, but it seriously affected the expression of TLL downstream of 2A peptide. SIGNIFICANCE AND IMPACT OF THE STUDY: The low production level is one of the limitation factors for decreasing the prices of enzymes and expanding their application in industry as the biocatalysts. This research focuses on developing lipase isozyme co-expression strategies in Pichia pastoris to enhance the expression level of overall lipase isozymes which catalyse the same reaction. The Kex2-mediated co-expression strategy of lipase isozymes could potentially enhance the overall isozyme expression, and isozyme co-expression might provide a new direction for improving the recombinant isozyme expression, and decreasing the production and application prices of these mixed enzymes as biocatalysts.

High level expression of ß-mannanase (RmMan5A) in Pichia pastoris for partially hydrolyzed guar gum production.

Partially hydrolyzed guar gum (PHGG), an important supplemental dietary fiber, has been used as food ingredient in many industries. In this study, a novel ß-mannanase gene (RmMan5A) from Rhizomucor miehei was successfully expressed in Pichia pastoris and subjected for PHGG production. Enzyme activity of fermentation supernatant reached 85,200UmL-1 after 168h high cell density fermentation. The purified RmMan5A exhibited the highest enzyme activity at pH 7.0 and 65°C. RmMan5A was then employed for guar gum hydrolysis and PHGG obtained demonstrated a weight-average molecular weight (Mw) of 2.5×104Da. Total dietary fiber accounted 90.6% of PHGG and 24.9% (w/w) of PHGG were identified as manno-oligosaccharides with degree of polymerization<7. PHGG was further fractionated (F1-F4) by gradual ethanol precipitation. PHGG F1 with an Mw value of 3.6×104Da and a mannose/galactose (M/G) ratio of 1.47 was precipitated initially, followed by PHGG F2 and F3 which showed lower Mw and higher M/G ratio. According to the structure analysis, the distribution of α-d-galactose of PHGG F1 was compact and regular, and that of other fractions was more random. A suitable ß-mannanase for PHGG production and some useful information of PHGG are provided in this paper.

Establishment and application of a modified membrane-blot assay for Rhizomucor miehei lipases aimed at improving their methanol tolerance and thermostability.

Directed evolution has been proved an effective way to improve the stability of proteins, but high throughput screening assays for directed evolution with simultaneous improvement of two or more properties are still rare. In this study, we aimed to establish a membrane-blot assay for use in the high-throughput screening of Rhizomucor miehei lipases (RMLs). With the assistance of the membrane-blot screening assay, a mutant E47K named G10 that showed improved thermal stability was detected in the first round of error-prone PCR. Using G10 as the parent, two variants G10-11 and G10-20 that showed improved thermal stability and methanol tolerance without loss of activity compared to the wild type RML were obtained. The T5060-value of G10-11 and G10-20 increased by 12°C and 6.5°C, respectively. After incubation for 1h, the remaining residual activity of G10-11 and G10-20 was 63.45% and 74.33%, respectively, in 50% methanol, and 15.98% and 30.22%, respectively, in 80% methanol. Thus, we successfully developed a membrane-blot assay that could be used for the high-throughput screening of RMLs with improved thermostability and methanol tolerance. Based on our findings, we believe that our newly developed membrane-blot assay will have potential applications in directed evolution in the future.

The first description of a hormone-sensitive lipase from a basidiomycete: Structural insights and biochemical characterization revealed Bjerkandera adusta BaEstB as a novel esterase.

The heterologous expression and characterization of a Hormone-Sensitive Lipases (HSL) esterase (BaEstB) from the Basidiomycete fungus Bjerkandera adusta is reported for the first time. According to structural analysis, amino acid similarities and conservation of particular motifs, it was established that this enzyme belongs to the (HSL) family. The cDNA sequence consisted of 969 nucleotides, while the gene comprised 1133, including three introns of 57, 50, and 57 nucleotides. Through three-dimensional modeling and phylogenetic analysis, we conclude that BaEstB is an ortholog of the previously described RmEstB-HSL from the phylogenetically distant fungus Rhizomucor miehei. The purified BaEstB was characterized in terms of its specificity for the hydrolysis of different acyl substrates confirming its low lipolytic activity and a noticeable esterase activity. The biochemical characterization of BaEstB, the DLS analysis and the kinetic parameters determination revealed this enzyme as a true esterase, preferentially found in a dimeric state, displaying activity under alkaline conditions and relative low temperature (pH = 10, 20°C). Our data suggest that BaEstB is more active on substrates with short acyl chains and bulky aromatic moieties. Phylogenetic data allow us to suggest that a number of fungal hypothetical proteins could belong to the HSL family.

Simultaneous lactic acidification and coagulation by using recombinant Lactococcus lactis strain.

AIMS: This study was an attempt to create a novel milk clotting procedure using a recombinant bacterium capable of milk coagulation. METHODS AND RESULTS: The Rhizomucor pusillus proteinase (RPP) gene was sub-cloned into a pALF expression vector. The recombinant pALF-RPP vector was then electro-transferred into Lactococcus lactis. Finally, the milk coagulation ability of recombinant L. lactis carrying a RPP gene was evaluated. Nucleotide sequencing of DNA insertion from the clone revealed that the RPP activity corresponded to an open reading frame consisting of 1218 bp coding for a 43·45 kDa RPP protein. The RPP protein assay results indicated that the highest RPP enzyme expression with 870 Soxhlet units (SU) per ml and 7914 SU/OD were obtained for cultures which were incubated at pH 5·5 and 30°C. Interestingly, milk coagulation was observed after 205 min of inoculating milk with recombinant L. lactis carrying the RPP gene. CONCLUSION: The recombinant L. lactis carrying RPP gene has the ability to function as a starter culture for acidifying and subsequently coagulating milk by producing RPP as a milk coagulant agent. SIGNIFICANCE AND IMPACT OF THE STUDY: Creating a recombinant starter culture bacterium that is able to coagulate milk. It is significant because the recombinant L. lactis has the ability to work as a starter culture and milk coagulation agent.

Purification and Properties of Extracellular Lipases with Transesterification Activity and 1,3-Regioselectivity from Rhizomucor miehei and Rhizopus oryzae.

Rhizomucor miehei NRRL 5282 and Rhizopus oryzae NRRL 1526 can produce lipases with high synthetic activities in wheat bran-based solid-state culture. In this study, the purification and biochemical characterization of the lipolytic activities of these lipases are presented. SDS-PAGE indicated a molecular mass of about 55 and 35 kDa for the purified R. miehei and Rh. oryzae enzymes, respectively. p-Nitrophenyl palmitate (pNPP) hydrolysis was maximal at 40°C and pH 7.0 for the R. miehei lipase, and at 30°C and pH 5.2 for the Rh. oryzae enzyme. The enzymes showed almost equal affinity to pNPP, but the Vmax of the Rh. oryzae lipase was about 1.13 times higher than that determined for R. miehei using the same substrate. For both enzymes, a dramatic loss of activity was observed in the presence of 5 mM Hg2+, Zn2+, or Mn2+, 10 mM N-bromosuccinimide or sodium dodecyl sulfate, and 5-10% (v/v) of hexanol or butanol. At the same time, they proved to be extraordinarily stable in the presence of n-hexane, cyclohexane, n-heptane, and isooctane. Moreover, isopentanol up to 10% (v/v) and propionic acid in 1 mM concentrations increased the pNPP hydrolyzing activity of R. miehei lipase. Both enzymes had 1,3-regioselectivity, and efficiently hydrolyzed p-nitrophenyl (pNP) esters with C8-C16 acids, exhibiting maximum activity towards pNP-caprylate (R. miehei) and pNP-dodecanoate (Rh. oryzae). The purified lipases are promising candidates for various biotechnological applications.