A novel extracellular esterase from Bacillus subtilis and its conversion to a monoacylglycerol hydrolase

Biodegradation of Polyurethane by Fungi Isolated from Industrial Wastewater-A Sustainable Approach to Plastic Waste Management

Polyurethane (PU) is a type of polymer, which exists in various forms in the environment. Very few studies are available concerning the structure or enzymatic mechanism of the microbial community, which can degrade PU. Degradation of PU remains a difficult problem with respect to the environmental and biological disciplines. This study mainly focused on identifying the micro-organisms able to degrade polyurethane and confirming the degradation by performing a plate assay, Sturm test and scanning electron microscopy. Optimal culture conditions for maximum PU degradation were also analyzed through classical methods. A soil burial test was conducted by placing polyurethane films in the soil for one month, and the microbe growing on the surface of polyurethane films-with a maximum degradation of 55%-was isolated and identified as Aspergillus versicolor (ARF5). The culture medium was also optimized with different physical and chemical parameters for maximum PU degradation. The presence of CO2 as a by-product of PU biodegradation was confirmed through the Sturm test.

A polylactic acid degrading lipase from Bacillus safensis: Characterization and structural analysis

A polylactic acid degrading triacylglycerol lipase (TGL) was identified from Bacillus safensis based on genome annotation and validated by real-time quantitative PCR. TGL displayed optimal activity at pH 9.0 and 55 °C. It maintained stability at pH 9.0 and temperatures 45 °C. The activity of TGL was found to benefit from the presence of potassium sodium ions, and low concentrations of Triton X-100. The TGL could erode the surface of polylactic acid films and increase its hydrophilicity. The hydrolysis products of polylactic acid by TGL were lactate monomer and dimer. TGL contains a classical catalytic triad structure of lipase (Ser77, Asp133, and His156) and an Ala-X-Ser-X-Gly sequence. Compared with some lipases produced by the same genus Bacillus, TGL is highly conserved in its amino acid sequence, mainly reflected in the amino acid residues that exercise the enzyme activity, including the catalytic activity center and the substrate binding sites.

Supra-biological performance of immobilized enzymes enabled by chaperone-like specific non-covalent interactions

Designing complex synthetic materials for enzyme immobilization could unlock the utility of biocatalysis in extreme environments. Inspired by biology, we investigate the use of random copolymer brushes as dynamic immobilization supports that enable supra-biological catalytic performance of immobilized enzymes. This is demonstrated by immobilizing Bacillus subtilis Lipase A on brushes doped with aromatic moieties, which can interact with the lipase through multiple non-covalent interactions. Incorporation of aromatic groups leads to a 50 °C increase in the optimal temperature of lipase, as well as a 50-fold enhancement in enzyme activity. Single-molecule FRET studies reveal that these supports act as biomimetic chaperones by promoting enzyme refolding and stabilizing the enzyme's folded and catalytically active state. This effect is diminished when aromatic residues are mutated out, suggesting the importance of π-stacking and π-cation interactions for stabilization. Our results underscore how unexplored enzyme-support interactions may enable uncharted opportunities for using enzymes in industrial biotransformations.

Perspectives on the Role of Enzymatic Biocatalysis for the Degradation of Plastic PET

Plastics are highly durable and widely used materials. Current methodologies of plastic degradation, elimination, and recycling are flawed. In recent years, biodegradation (the usage of microorganisms for material recycling) has grown as a valid alternative to previously used methods. The evolution of bioengineering techniques and the discovery of novel microorganisms and enzymes with degradation ability have been key. One of the most produced plastics is PET, a long chain polymer of terephthalic acid (TPA) and ethylene glycol (EG) repeating monomers. Many enzymes with PET degradation activity have been discovered, characterized, and engineered in the last few years. However, classification and integrated knowledge of these enzymes are not trivial. Therefore, in this work we present a summary of currently known PET degrading enzymes, focusing on their structural and activity characteristics, and summarizing engineering efforts to improve activity. Although several high potential enzymes have been discovered, further efforts to improve activity and thermal stability are necessary.

Sajedi R. Thermostability of Ctenophore and Coelenterate Ca2+-Regulated Apo-photoproteins: A Comparative Study

The stabilities of Ca²⁺-regulated ctenophore and coelenterate apo-photoproteins, apo-mnemiopsin (apo-Mne) and apo-aequorin (apo-Aeq), respectively, were compared biochemically, biophysically, and structurally. Despite high degrees of structural and functional conservation, drastic variations in stability and structural dynamics were found between the two proteins. Irreversible thermoinactivation experiments were performed upon incubation of apo-photoproteins at representative temperatures. The inactivation rate constants (k_inact) at 50 °C were determined to be 0.001 and 0.004 min^-1 for apo-Mne and apo-Aeq, respectively. Detailed analysis of the inactivation process suggests that the higher thermostability of apo-Mne is due to the higher activation energy (E_a) and subsequently higher values of ΔH* and ΔG* at a given temperature. According to molecular dynamics simulation studies, the higher hydrogen bond, electrostatic, and van der Waals energies in apo-Mne can validate the relationship between the thermal adaptation of apo-Mne and the energy barrier for the inactivation process. Our results show that favorable residues for protein thermostability such as hydrophobic, charged, and adopted α-helical structure residues are more frequent in the apo-Mne structure. Although the effect of acrylamide on fluorescence quenching suggests that the local flexibility in regions around Trp and Tyr residues of apo-Aeq is higher than that of apo-Mne, which results in it having a better ability to penetrate acrylamide molecules, the root-mean-square fluctuation of helix A in apo-Mne is higher than that in apo-Aeq. It seems that the greater flexibility of apo-Mne in these regions may be considered as a determining factor, affecting the thermal stability of apo-Mne through a balance between structural rigidity and flexibility.

Endogenous Enzymes Enable Antimicrobial Activity

In light of the continued threat of antimicrobial-resistant bacteria, new strategies to expand the repertoire of antimicrobial compounds are necessary. Prodrugs are an underexploited strategy in this effort. Here, we report on the enhanced antimicrobial activity of a prodrug toward bacteria having an enzyme capable of its activation. A screen led us to the sulfurol ester of the antibiotic trans-3-(4-chlorobenzoyl)acrylic acid. An endogenous esterase makes Mycolycibacterium smegmatis sensitive to this prodrug. Candidate esterases were identified, and their heterologous production made Escherichia coli sensitive to the ester prodrug. Taken together, these data suggest a new approach to the development of antimicrobial compounds that takes advantage of endogenous enzymatic activities to target specific bacteria.

Main Structural Targets for Engineering Lipase Substrate Specificity

Microbial lipases represent one of the most important groups of biotechnological biocatalysts. However, the high-level production of lipases requires an understanding of the molecular mechanisms of gene expression, folding, and secretion processes. Stable, selective, and productive lipase is essential for modern chemical industries, as most lipases cannot work in different process conditions. However, the screening and isolation of a new lipase with desired and specific properties would be time consuming, and costly, so researchers typically modify an available lipase with a certain potential for minimizing cost. Improving enzyme properties is associated with altering the enzymatic structure by changing one or several amino acids in the protein sequence. This review detailed the main sources, classification, structural properties, and mutagenic approaches, such as rational design (site direct mutagenesis, iterative saturation mutagenesis) and direct evolution (error prone PCR, DNA shuffling), for achieving modification goals. Here, both techniques were reviewed, with different results for lipase engineering, with a particular focus on improving or changing lipase specificity. Changing the amino acid sequences of the binding pocket or lid region of the lipase led to remarkable enzyme substrate specificity and enantioselectivity improvement. Site-directed mutagenesis is one of the appropriate methods to alter the enzyme sequence, as compared to random mutagenesis, such as error-prone PCR. This contribution has summarized and evaluated several experimental studies on modifying the substrate specificity of lipases.

Directed evolution of a genetically encoded immobilized lipase for the efficient production of biodiesel from waste cooking oil

BACKGROUND

We have recently developed a one-step, genetically encoded immobilization approach based on fusion of a target enzyme to the self-crystallizing protein Cry3Aa, followed by direct production and isolation of the fusion crystals from Bacillus thuringiensis. Using this approach, Bacillus subtilis lipase A was genetically fused to Cry3Aa to produce a Cry3Aa-lipA catalyst capable of the facile conversion of coconut oil into biodiesel over 10 reaction cycles. Here, we investigate the fusion of another lipase to Cry3Aa with the goal of producing a catalyst suitable for the conversion of waste cooking oil into biodiesel.

RESULTS

Genetic fusion of the Proteus mirabilis lipase (PML) to Cry3Aa allowed for the production of immobilized lipase crystals (Cry3Aa-PML) directly in bacterial cells. The fusion resulted in the loss of PML activity, however, and so taking advantage of its genetically encoded immobilization, directed evolution was performed on Cry3Aa-PML directly in its immobilized state in vivo. This novel strategy allowed for the selection of an immobilized PML mutant with 4.3-fold higher catalytic efficiency and improved stability. The resulting improved Cry3Aa-PML catalyst could be used to catalyze the conversion of waste cooking oil into biodiesel for at least 15 cycles with minimal loss in conversion efficiency.

CONCLUSIONS

The genetically encoded nature of our Cry3Aa-fusion immobilization platform makes it possible to perform both directed evolution and screening of immobilized enzymes directly in vivo. This work is the first example of the use of directed evolution to optimize an enzyme in its immobilized state allowing for identification of a mutant that would unlikely have been identified from screening of its soluble form. We demonstrate that the resulting Cry3Aa-PML catalyst is suitable for the recyclable conversion of waste cooking oil into biodiesel.

pH-Induced Rotation of Lidless Lipase LipA from Bacillus subtilis at Lipase-Detergent Interface

Lipases exhibit a unique process during the catalysis of the hydrolysis of triglyceride substrates called interfacial activation. Surfactants are used as cosolvents with water not only to offer a less polar environment to the lipases needed for their interfacial activation but also to solvate the substrate which are poorly soluble in water. However, the presence of detergent in the medium can affect both the lipase and the substrate, making the construction of a microkinetic model for lipase activity in the presence of the detergent difficult. Herein, we study the interfacial activation of a lidless lipase LipA from Bacillus subtilis using extensive atomistic molecular dynamics simulations at different concentrations of the surfactant, Thesit (C12E8), at two pH values. Residues which bind to the monomeric detergent are found to be the same as the ones which have been reported earlier to bind to the substrate. Very importantly, a pH-induced rotation of the enzyme with respect to surfactant aggregate has been observed which not only explains the experimentally observed pH-dependent enzymatic activity of this lidless lipase, but also suggests its reorientation at an aqueous-lipodophilic interface.

Synthesis, characterization and application of lipase-conjugated citric acid-coated magnetic nanoparticles for ester synthesis using waste frying oil

In the present work, magnetic nanoparticles (MNPs) were prepared by chemical precipitation of trivalent and divalent iron ions which were functionalized using citric acid. The bacterial isolate Staphylococcus epidermidis KX781317 was isolated from oil-contaminated site. The isolate produced lipase, which was purified and immobilized on magnetic nanoparticles (MNPs) for ester synthesis from waste frying oil (WFO). The characterization of MNPs employed conventional TEM, XRD and FTIR techniques. TEM analysis of MNPs showed the particle size in the range of 20-50 nm. FTIR spectra revealed the binding of citric acid to Fe₃O₄ and lipase on citric acid-coated MNPs. The citric acid-coated MNPs and lipase-conjugated citric acid-coated MNPs had similar XRD patterns which indicate MNPs could preserve their magnetic properties. The maximum immobilization efficiency 98.21% of lipase-containing citric acid-coated MNPs was observed at ratio 10:1 of Cit-MNPs:lipase. The pH and temperature optima for lipase conjugated with Cit-MNPs were 7 and 35 °C, respectively. Isobutanol was found to be an effective solvent for ester synthesis and 1:2 ratio of oil:alcohol observed significant for ester formation. The ester formation was determined using TLC and the % yield of ester conversion was calculated. The rate of ester formation is directly proportional to the enzyme load. Formed esters were identified as isobutyl laurate ester and isobutyl myristate ester through GC-MS analysis.

Online measurement of the respiratory activity in shake flasks enables the identification of cultivation phases and patterns indicating recombinant protein production in various Escherichia coli host strains

Escherichia coli is commonly used for recombinant protein production with many available host strains. Screening experiments are often performed in batch mode using shake flasks and evaluating only the final product concentration. This conventional approach carries the risk of missing the best strain due to limited monitoring capabilities. Thus, this study focuses on investigating the general suitability of online respiration measurement for selecting expression hosts for heterologous protein production. The oxygen transfer rate (OTR) for different T7-RNA polymerase-dependent Escherichia coli expression strains was compared under inducing and noninducing conditions. As model enzymes, a lipase A from Bacillus subtilis (BSLA) and a 3-hydroxybutyryl-CoA dehydrogenase from Thermus thermophilus (HBD) were chosen. Four strains were compared during expression of both enzymes in autoinduction medium. Additionally, four strains were compared during expression of the BSLA with IPTG induction. It was found that the metabolic burden during recombinant protein production induces a phase of constant OTR, while undisturbed cell growth with no or little product formation is indicated by an exponential increase. This pattern is independent of the host strain, expressed enzyme, and induction method. Furthermore, the OTR gives information about carbon source consumption, biomass formation, and the transition from production to noninduced second growth phase, thereby ensuring a fair comparison of different strains. In conclusion, online monitoring of the respiration activity is suited to qualitatively identify, if a recombinant protein is produced by a strain or not. Furthermore, laborious offline sampling is avoided. Thus, the technique is easier and faster compared to conventional approaches. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:315-327, 2018.

Construction of a novel lipolytic fusion biocatalyst GDEst-lip for industrial application

The gene encoding esterase (GDEst-95) from Geobacillus sp. 95 was cloned and sequenced. The resulting open reading frame of 1497 nucleotides encoded a protein with calculated molecular weight of 54.7 kDa, which was classified as a carboxylesterase with an identity of 93-97% to carboxylesterases from Geobacillus bacteria. This esterase can be grouped into family VII of bacterial lipolytic enzymes, was active at broad pH (7-12) and temperature (5-85 °C) range and displayed maximum activity toward short acyl chain p-nitrophenyl (p-NP) esters. Together with GD-95 lipase from Geobacillus sp. strain 95, GDEst-95 esterase was used for construction of fused chimeric biocatalyst GDEst-lip. GDEst-lip esterase/lipase possessed high lipolytic activity (600 U/mg), a broad pH range of 6-12, thermoactivity (5-85 °C), thermostability and resistance to various organic solvents or detergents. For these features GDEst-lip biocatalyst has high potential for applications in various industrial areas. In this work the effect of additional homodomains on monomeric GDEst-95 esterase and GD-95 lipase activity, thermostability, substrate specificity and catalytic properties was also investigated. Altogether, this article shows that domain fusing strategies can modulate the activity and physicochemical characteristics of target enzymes for industrial applications.

New Insight into Old Bacillus Lipase: Solvent Stable Mesophilic Lipase Demonstrating Enzyme Activity towards Cold

BACKGROUND

Bacillus lipases are grouped in subfamily 1.4, which are the smallest known lipases having a molecular mass of 19.6 kDa. Lipases active in a wide range of temperatures, specifically at low temperatures, have an advantage under low water conditions for industrial application.

METHODS

The lipase gene was cloned and expressed in Escherichia coli. The protein was purified and biochemically characterized in detail.

RESULTS

A lipase gene was cloned from a mesophilic Bacillus isolate. Sequence analysis revealed an open reading frame of 633 bp in length. The predicted molecular mass of protein was 22.6 kDa. The purified enzyme displayed optimal activity at 35 °C and pH 8.0. Interestingly, this mesophilic enzyme was also cold active showing retention of 75 and 55% relative enzyme activity at 20 and 10 °C, respectively. The purified lipase was stable in various organic solvents (50% v/v) and ionic liquids (5% v/v). The enzyme displayed maximum activity with paranitrophenyl laurate (C12). kcat/Km values for the purified lipase were calculated to be 5.8 ± 0.6 × 10(-6).

CONCLUSIONS

The lipase showed tolerance to various solvents as well as activity at low temperature. Therefore, this lipase might be of great potential to be employed in various industrial applications.

A flow cytometer-based whole cell screening toolbox for directed hydrolase evolution through fluorescent hydrogels

A high-throughput whole cell flow cytometer screening toolbox for hydrolases was validated by identification of improved esterase, lipase and cellulase variants.

Degradation of poly(ε-caprolactone) (PCL) by a newly isolated Brevundimonas sp. strain MRL-AN1 from soil

A poly(ε-caprolactone) (PCL)-degrading bacterium designated as strain MRL-AN1 was isolated from soil. The bacterium was identified as Brevundimonas sp. strain MRL-AN1 through biochemical tests and 16S rRNA gene sequencing. Scanning electron microscopy and Fourier transform infrared spectroscopy results confirmed the degradation of PCL by strain MRL-AN1. An extracellular PCL depolymerase was purified to homogeneity by column chromatography and molecular weight was estimated to be approximately 63.49 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. PCL depolymerase could degrade not only PCL but also other aliphatic polyesters. The enzyme was stable at wide range of temperature (20-45°C) and pH (5-9) as well as stable in the presence of various metal ions, surfactants and organic solvents. Phenylmethylsulfonyl fluoride inhibited enzyme activity that indicates this enzyme belongs to the serine hydrolase family. It is concluded from the results that the enzymes from strain MRL-AN1 might be applied in the process of biochemical monomer recycling in the polyester-contaminated environments.

In Bacillus subtilis LutR is part of the global complex regulatory network governing the adaptation to the transition from exponential growth to stationary phase

The lutR gene, encoding a product resembling a GntR-family transcriptional regulator, has previously been identified as a gene required for the production of the dipeptide antibiotic bacilysin in Bacillus subtilis. To understand the broader regulatory roles of LutR in B. subtilis, we studied the genome-wide effects of a lutR null mutation by combining transcriptional profiling studies using DNA microarrays, reverse transcription quantitative PCR, lacZ fusion analyses and gel mobility shift assays. We report that 65 transcriptional units corresponding to 23 mono-cistronic units and 42 operons show altered expression levels in lutR mutant cells, as compared with lutR + wild-type cells in early stationary phase. Among these, 11 single genes and 25 operons are likely to be under direct control of LutR. The products of these genes are involved in a variety of physiological processes associated with the onset of stationary phase in B. subtilis, including degradative enzyme production, antibiotic production and resistance, carbohydrate utilization and transport, nitrogen metabolism, phosphate uptake, fatty acid and phospholipid biosynthesis, protein synthesis and translocation, cell-wall metabolism, energy production, transfer of mobile genetic elements, induction of phage-related genes, sporulation, delay of sporulation and cannibalism, and biofilm formation. Furthermore, an electrophoretic mobility shift assay performed in the presence of both SinR and LutR revealed a close overlap between the LutR and SinR targets. Our data also revealed a significant overlap with the AbrB regulon. Together, these findings reveal that LutR is part of the global complex, interconnected regulatory systems governing adaptation of bacteria to the transition from exponential growth to stationary phase.

Biochemical characterization of a first fungal esterase from Rhizomucor miehei showing high efficiency of ester synthesis

BACKGROUND

Esterases with excellent merits suitable for commercial use in ester production field are still insufficient. The aim of this research is to advance our understanding by seeking for more unusual esterases and revealing their characterizations for ester synthesis.

METHODOLOGY/PRINCIPAL FINDINGS

A novel esterase-encoding gene from Rhizomucor miehei (RmEstA) was cloned and expressed in Escherichia coli. Sequence analysis revealed a 975-bp ORF encoding a 324-amino-acid polypeptide belonging to the hormone-sensitive lipase (HSL) family IV and showing highest similarity (44%) to the Paenibacillus mucilaginosus esterase/lipase. Recombinant RmEstA was purified to homogeneity: it was 34 kDa by SDS-PAGE and showed optimal pH and temperature of 6.5 and 45°C, respectively. The enzyme was stable to 50°C, under a broad pH range (5.0-10.6). RmEstA exhibited broad substrate specificity toward p-nitrophenol esters and short-acyl-chain triglycerols, with highest activities (1,480 U mg(-1) and 228 U mg(-1)) for p-nitrophenyl hexanoate and tributyrin, respectively. RmEstA efficiently synthesized butyl butyrate (92% conversion yield) when immobilized on AOT-based organogel.

CONCLUSION

RmEstA has great potential for industrial applications. RmEstA is the first reported esterase from Rhizomucor miehei.

A low molecular mass cutinase of Thielavia terrestris efficiently hydrolyzes poly(esters)

A low molecular mass cutinase (designated TtcutA) from Thielavia terrestris was purified and biochemically characterized. The thermophilic fungus T. terrestris CAU709 secreted a highly active cutinase (90.4 U ml−1) in fermentation broth containing wheat bran as the carbon source. The cutinase was purified 19-fold with a recovery yield of 4.8 %. The molecular mass of the purified TtcutA was determined as 25.3 and 22.8 kDa using SDS-PAGE and gel filtration, respectively. TtcutA displayed optimal activity at pH 4.0 and 50 °C. It was highly stable up to 65 °C and in the broad pH range 2.5–10.5. Extreme stability in high concentrations (80 %, v/v) of solvents such as methanol, ethanol, acetone, acetonitrile, isopropanol, and dimethyl sulfoxide was observed for the enzyme. The K  m values for this enzyme towards p-nitrophenyl (pNP) acetate, pNP butyrate, and pNP caproate were 7.7, 1.0, and 0.52 mM, respectively. TtcutA was able to efficiently degrade various ester polymers, including cutin, polyethylene terephthalate (PET), polycaprolactone (PCL), and poly(butylene succinate) (PBS) at hydrolytic rates of 3 μmol h−1 mg−1 protein, 1.1 mg h−1 mg−1 protein, 203.6 mg h−1 mg−1 protein, and 56.4 mg h−1 mg−1 protein, respectively. Because of these unique biochemical properties, TtcutA of T. terrestris may be useful in various industrial applications in the future.

Identification and functional analysis of gene cluster involvement in biosynthesis of the cyclic lipopeptide antibiotic pelgipeptin produced by Paenibacillus elgii

Background

Pelgipeptin, a potent antibacterial and antifungal agent, is a non-ribosomally synthesised lipopeptide antibiotic. This compound consists of a β-hydroxy fatty acid and nine amino acids. To date, there is no information about its biosynthetic pathway.

Results

A potential pelgipeptin synthetase gene cluster (plp) was identified from Paenibacillus elgii B69 through genome analysis. The gene cluster spans 40.8 kb with eight open reading frames. Among the genes in this cluster, three large genes, plpD, plpE, and plpF, were shown to encode non-ribosomal peptide synthetases (NRPSs), with one, seven, and one module(s), respectively. Bioinformatic analysis of the substrate specificity of all nine adenylation domains indicated that the sequence of the NRPS modules is well collinear with the order of amino acids in pelgipeptin. Additional biochemical analysis of four recombinant adenylation domains (PlpD A1, PlpE A1, PlpE A3, and PlpF A1) provided further evidence that the plp gene cluster involved in pelgipeptin biosynthesis.

Conclusions

In this study, a gene cluster (plp) responsible for the biosynthesis of pelgipeptin was identified from the genome sequence of Paenibacillus elgii B69. The identification of the plp gene cluster provides an opportunity to develop novel lipopeptide antibiotics by genetic engineering.

Purification and characterization of a highly thermostable esterase from the actinobacterium Geodermatophilus obscurus strain G20

Intracellular thermostable esterase produced by the extremophilic Geodermatophilus obscurus G20 was purified to homogeneity by a heat treatment, followed by an anion-exchange chromatography, and then characterized. The molecular weight of the purified enzyme determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was shown to be approximatively 55 kDa. The enzyme showed an optimal activity between pH 8.0 and 9.0 and was stable in the pH range 7.0-10.0. Moreover, it is highly thermostable, with a residual activity greater than 90% after incubation at 80 °C for more than 10 h. The enzyme showed preference for esters of p -nitrophenol with short chain fatty acid. When the p -nitrophenyl acetate (C2) was used as substrate, the Michaelis-Menten constant (K(m) ) and maximum velocity for the reaction (V(max) ) of esterase were 400 μM and 2500 U/mg protein, respectively. The effect of phenylmethanesulphonyl fluoride (PMSF), a serine-specific inhibitor, on the enzyme activity suggested that the thermostable esterase belong to the serine hydrolase group. Because of its high thermostability, activity at alkaline pH, tolerance to methanol and various metal ions and specificity for short chain fatty acids, this enzyme showed high potential for use in biocatalysis. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim).

Heterologous expression systems for lipases: a review

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

Mechanism of acetaldehyde-induced deactivation of microbial lipases

Background

Microbial lipases represent the most important class of biocatalysts used for a wealth of applications in organic synthesis. An often applied reaction is the lipase-catalyzed transesterification of vinyl esters and alcohols resulting in the formation of acetaldehyde which is known to deactivate microbial lipases, presumably by structural changes caused by initial Schiff-base formation at solvent accessible lysine residues. Previous studies showed that several lipases were sensitive toward acetaldehyde deactivation whereas others were insensitive; however, a general explanation of the acetaldehyde-induced inactivation mechanism is missing.

Results

Based on five microbial lipases from Candida rugosa, Rhizopus oryzae, Pseudomonas fluorescens and Bacillus subtilis we demonstrate that the protonation state of lysine ε-amino groups is decisive for their sensitivity toward acetaldehyde. Analysis of the diverse modification products of Bacillus subtilis lipases in the presence of acetaldehyde revealed several stable products such as α,β-unsaturated polyenals, which result from base and/or amino acid catalyzed aldol condensation of acetaldehyde. Our studies indicate that these products induce the formation of stable Michael-adducts at solvent-accessible amino acids and thus lead to enzyme deactivation. Further, our results indicate Schiff-base formation with acetaldehyde to be involved in crosslinking of lipase molecules.

Conclusions

Differences in stability observed with various commercially available microbial lipases most probably result from different purification procedures carried out by the respective manufacturers. We observed that the pH of the buffer used prior to lyophilization of the enzyme sample is of utmost importance. The mechanism of acetaldehyde-induced deactivation of microbial lipases involves the generation of α,β-unsaturated polyenals from acetaldehyde which subsequently form stable Michael-adducts with the enzymes. Lyophilization of the enzymes from buffer at pH 6.0 can provide an easy and effective way to stabilize lipases toward inactivation by acetaldehyde.

Molecular cloning, over expression and characterization of thermoalkalophilic esterases isolated from Geobacillus sp

Due to potential use for variety of biotechnological applications, genes encoding thermoalkalophilic esterase from three different Geobacillus strains isolated from thermal environmental samples in Balçova (Agamemnon) geothermal site were cloned and respective proteins were expressed in Escherichia coli (E.coli) and characterized in detail. Three esterases (Est1, Est2, Est3) were cloned directly by PCR amplification using consensus degenerate primers from genomic DNA of the strains Est1, Est2 and Est3 which were from mud, reinjection water and uncontrolled thermal leak, respectively. The genes contained an open reading frame (ORF) consisting of 741 bp for Est1 and Est2, which encoded 246 amino acids and ORF of Est3 was 729 bp encoded 242 amino acids. The esterase genes were expressed in E. coli and purified using His-Select HF nickel affinity gel. The molecular mass of the recombinant enzyme for each esterase was approximately 27.5 kDa. The three esterases showed high specific activity toward short chain p-NP esters. Recombinant Est1, Est2, Est3 have exhibited similar activity and the highest esterase activity of 1,100 U/mg with p-nitrophenyl acetate (pNPC(2)) as substrate was observed with Est1. All three esterase were most active around 65°C and pH 9.5-10.0. The effect of organic solvents, several metal ions, inhibitors and detergents on enzyme activity for purified Est1, Est2, Est3 were determined separately and compared.

Response of bacteria in the deep-sea sediments and the Antarctic soils to carbohydrates: effects on ectoenzyme activity and bacterial community

The response of bacteria to various carbohydrates in the deep-sea sediments and the Antarctic soils was investigated using cellulose, chitin, and olive oil. It was found that the carbohydrates significantly increased the corresponding specific ectoenzyme activity (beta-glucosidase, beta-N-acetylglucosaminidase, lipase) in the samples from deep-sea sediments. In the case of Antarctic soil samples, the cellulose or olive oil amendments had minor or no effect on beta-glucosidase or lipase activity, except the chitin which stimulated beta-N-acetylglucosaminidase production. The responses of the bacteria in the deep-sea sediment sample WP02-3 and the Antarctic soil sample CC-TY2 towards the chitin amendment were further analyzed. Chitin amendments were shown to stimulate the ectoenzyme activity in all the tested sediments and the soils. The bacterial response before and after the carbohydrates amendments were compared by denaturing gradient gel electrophoresis and quantitative competitive polymerase chain reaction. Significant changes were found in the structure and density of the bacterial community in the deep sea sediments as compared to the Antarctic soil sample, where the effects were relatively lower. There was no change in the bacterial population in both studied samples in response to carbohydrates amendments. These data indicate that the bacterial communities in the oligotrophic deep-sea sediments are more dynamic than that in the Antarctic soils as they respond to the nutrient sources efficiently by regulation of ectoenzyme activity and/or changing community structure.

A novel lipolytic enzyme, YcsK (LipC), located in the spore coat of Bacillus subtilis, is involved in spore germination

The predicted amino acid sequence of Bacillus subtilis ycsK exhibits similarity to the GDSL family of lipolytic enzymes. Northern blot analysis showed that ycsK mRNA was first detected from 4 h after the onset of sporulation and that transcription of ycsK was dependent on SigK and GerE. The fluorescence of the YcsK-green fluorescent protein fusion protein produced in sporulating cells was detectable in the mother cell but not in the forespore compartment under fluorescence microscopy, and the fusion protein was localized around the developing spores dependent on CotE, SafA, and SpoVID. Inactivation of the ycsK gene by insertion of an erythromycin resistance gene did not affect vegetative growth or spore resistance to heat, lysozyme, or chloroform. The germination of ycsK spores in a mixture of L-asparagine, D-glucose, D-fructose, and potassium chloride and LB medium was also the same as that of wild-type spores, but the mutant spores were defective in L-alanine-stimulated germination. In addition, zymogram analysis demonstrated that the YcsK protein heterologously expressed in Escherichia coli showed lipolytic activity. We therefore propose that ycsK should be renamed lipC. This is the first study of a bacterial spore germination-related lipase.

Isolation and characterization of a novel lipase from a metagenomic library of tidal flat sediments: evidence for a new family of bacterial lipases

We cloned lipG, which encoded a lipolytic enzyme, from a Korean tidal flat metagenomic library. LipG was related to six putative lipases previously identified only in bacterial genome sequences. These enzymes comprise a new family. We partially characterized LipG, providing the first experimental data for a member of this family.