High-level expression and characterization of a novel cutinase from Malbranchea cinnamomea suitable for butyl butyrate production

Novel polyurethane-degrading cutinase BaCut1 from Blastobotrys sp. G-9 with potential role in plastic bio-recycling

Environmental pollution caused by plastic waste has become global problem that needs to be considered urgently. In the pursuit of a circular plastic economy, biodegradation provides an attractive strategy for managing plastic wastes, whereas effective plastic-degrading microbes and enzymes are required. In this study, we report that Blastobotrys sp. G-9 isolated from discarded plastic in landfills is capable of depolymerizing polyurethanes (PU) and poly (butylene adipate-co-terephthalate) (PBAT). Strain G-9 degrades up to 60% of PU foam after 21 days of incubation at 28 ℃ by breaking down carbonyl groups via secretory hydrolase as confirmed by structural characterization of plastics and degradation products identification. Within the supernatant of strain G-9, we identify a novel cutinase BaCut1, belonging to the esterase family, that can reproduce the same effect. BaCut1 demonstrates efficient degradation toward commercial polyester plastics PU foam (0.5 mg enzyme/25 mg plastic) and agricultural film PBAT (0.5 mg enzyme/10 mg plastic) with 50% and 18% weight loss at 37 ℃ for 48 h, respectively. BaCut1 hydrolyzes PU into adipic acid as a major end-product with 42.9% recovery via ester bond cleavage, and visible biodegradation is also identified from PBAT, which is a beneficial feature for future recycling economy. Molecular docking, along with products distribution, elucidates a special substrate-binding modes of BaCut1 with plastic substrate analogue. BaCut1-mediated polyester plastic degradation offers an alternative approach for managing PU plastic wastes through possible bio-recycling.

Synthesis of Isoamyl Fatty Acid Ester, a Flavor Compound, by Immobilized Rhodococcus Cutinase

Isoamyl fatty acid esters (IAFEs) are widely used as fruity flavor compounds in the food industry. In this study, various IAFEs were synthesized from isoamyl alcohol and various fatty acids using a cutinase enzyme (Rcut) derived from Rhodococcus bacteria. Rcut was immobilized on methacrylate divinylbenzene beads and used to synthesize isoamyl acetate, butyrate, hexanoate, octanoate, and decanoate. Among them, Rcut synthesized isoamyl butyrate (IAB) most efficiently. Docking model studies showed that butyric acid was the most suitable substrate in terms of binding energy and distance from the active site serine (Ser114) γ-oxygen. Up to 250 mM of IAB was synthesized by adjusting reaction conditions such as substrate concentration, reaction temperature, and reaction time. When the enzyme reaction was performed by reusing the immobilized enzyme, the enzyme activity was maintained at least six times. These results demonstrate that the immobilized Rcut enzyme can be used in the food industry to synthesize a variety of fruity flavor compounds, including IAB.

ANCUT1, a novel thermoalkaline cutinase from Aspergillus nidulans and its application on hydroxycinnamic acids lipophilization

One of the four cutinases encoded in the Aspergillus nidulans genome, ANCUT1, is described here. Culture conditions were evaluated, and it was found that this enzyme is produced only when cutin is present in the culture medium, unlike the previously described ANCUT2, with which it shares 62% amino acid identity. The differences between them include the fact that ANCUT1 is a smaller enzyme, with experimental molecular weight and pI values of 22 kDa and 6, respectively. It shows maximum activity at pH 9 and 60 °C under assayed conditions and retains more than 60% of activity after incubation for 1 h at 60 °C in a wide range of pH values (6-10) after incubations of 1 or 3 h. It has a higher activity towards medium-chain esters and can modify long-chain length hydroxylated fatty acids constituting cutin. Its substrate specificity properties allow the lipophilization of alkyl coumarates, valuable antioxidants and its thermoalkaline behavior, which competes favorably with other fungal cutinases, suggests it may be useful in many more applications.

Identification and recombinant expression of a cutinase from Papiliotrema laurentii that hydrolyzes natural and synthetic polyesters

Given the multitude of extracellular enzymes at their disposal, many of which are designed to degrade nature's polymers (lignin, cutin, cellulose, etc.), fungi are adept at targeting synthetic polyesters with similar chemical composition. Microbial-influenced deterioration of xenobiotic polymeric surfaces is an area of interest for material scientists as these are important for the conservation of the underlying structural materials. Here, we describe the isolation and characterization of the Papiliotrema laurentii 5307AH (P. laurentii) cutinase, Plcut1. P. laurentii is basidiomycete yeast with the ability to disperse Impranil-DLN (Impranil), a colloidal polyester polyurethane, in agar plates. To test whether the fungal factor involved in this clearing was a secreted enzyme, we screened the ability of P. laurentii culture supernatants to disperse Impranil. Using size exclusion chromatography (SEC), we isolated fractions that contained Impranil-clearing activity. These fractions harbored a single ~22 kD band, which was excised and subjected to peptide sequencing. Homology searches using the peptide sequences identified, revealed that the protein Papla1 543643 (Plcut1) displays similarities to serine esterase and cutinase family of proteins. Biochemical assays using recombinant Plcut1 confirmed that this enzyme has the capability to hydrolyze Impranil, soluble esterase substrates, and apple cutin. Finally, we confirmed the presence of the Plcut1 in culture supernatants using a custom antibody that specifically recognizes this protein. The work shown here supports a major role for the Plcut1 in the fungal degradation of natural polyesters and xenobiotic polymer surfaces.IMPORTANCEFungi play a vital role in the execution of a broad range of biological processes that drive ecosystem function through production of a diverse arsenal of enzymes. However, the universal reactivity of these enzymes is a current problem for the built environment and the undesired degradation of polymeric materials in protective coatings. Here, we report the identification and characterization of a hydrolase from Papiliotrema laurentii 5307AH, an aircraft-derived fungal isolate found colonizing a biodeteriorated polymer-coated surface. We show that P. laurentii secretes a cutinase capable of hydrolyzing soluble esters as well as ester-based compounds forming solid surface coatings. These findings indicate that this fungus plays a significant role in biodeterioration through the production of a cutinase adept at degrading ester-based polymers, some of which form the backbone of protective surface coatings. The work shown here provides insights into the mechanisms employed by fungi to degrade xenobiotic polymers.

Synthesis of Short-Chain Alkyl Butyrate through Esterification Reaction Using Immobilized Rhodococcus Cutinase and Analysis of Substrate Specificity through Molecular Docking

Alkyl butyrate with fruity flavor is known as an important additive in the food industry. We synthesized various alkyl butyrates from various fatty alcohol and butyric acid using immobilized Rhodococcus cutinase (Rcut). Esterification reaction was performed in a non-aqueous system including heptane, isooctane, hexane, and cyclohexane. As a result of performing the alkyl butyrate synthesis reaction using alcohols of various chain lengths, it was found that the preference for the alcohol substrate had the following order: C6 > C4 > C8 > C10 > C2. Through molecular docking analysis, it was found that the greater the hydrophobicity of alcohol, the higher the accessibility to the active site of the enzyme. However, since the number of torsions increased as the chain length increased, it became difficult for the hydroxyl oxygen of the alcohol to access the ^γO of serine at the enzyme active site. These molecular docking results were consistent with substrate preference results of the Rcut enzyme. The Rcut maintained the synthesis efficiency at least for 5 days in isooctane solvent. We synthesized as much as 452 mM butyl butyrate by adding 100 mM substrate daily for 5 days and performing the reaction. These results show that Rcut is an efficient enzyme for producing alkyl butyrate used in the food industry.

Merging Plastics, Microbes, and Enzymes: Highlights from an International Workshop

In the Anthropocene, plastic pollution is a worldwide concern that must be tackled from different viewpoints, bringing together different areas of science. Microbial transformation of polymers is a broad-spectrum research topic that has become a keystone in the circular economy of fossil-based and biobased plastics. To have an open discussion about these themes, experts in the synthesis of polymers and biodegradation of lignocellulose and plastics convened within the framework of The Transnational Network for Research and Innovation in Microbial Biodiversity, Enzymes Technology and Polymer Science (MENZYPOL-NET), which was recently created by early-stage scientists from Colombia and Germany. In this context, the international workshop "Microbial Synthesis and Degradation of Polymers: Toward a Sustainable Bioeconomy" was held on 27 September 2021 via Zoom. The workshop was divided into two sections, and questions were raised for discussion with panelists and expert guests. Several key points and relevant perspectives were delivered, mainly related to (i) the microbial evolution driven by plastic pollution; (ii) the relevance of and interplay between polymer structure/composition, enzymatic mechanisms, and assessment methods in plastic biodegradation; (iii) the recycling and valorization of plastic waste; (iv) engineered plastic-degrading enzymes; (v) the impact of (micro)plastics on environmental microbiomes; (vi) the isolation of plastic-degrading (PD) microbes and design of PD microbial consortia; and (vii) the synthesis and applications of biobased plastics. Finally, research priorities from these key points were identified within the microbial, enzyme, and polymer sciences.

A Review of the Fungi That Degrade Plastic

Plastic has become established over the world as an essential basic need for our daily life. Current global plastic production exceeds 300 million tons annually. Plastics have many characteristics such as low production costs, inertness, relatively low weight, and durability. The primary disadvantage of plastics is their extremely slow natural degradation. The latter results in an accumulation of plastic waste in nature. The amount of plastic waste as of 2015 was 6300 million tons worldwide, and 79% of this was placed in landfills or left in the natural environment. Moreover, recent estimates report that 12,000 million tons of plastic waste will have been accumulated on the earth by 2050. Therefore, it is necessary to develop an effective plastic biodegradation process to accelerate the natural degradation rate of plastics. More than 400 microbes have been identified as capable of plastic degradation. This is the first paper of the series on plastic-degrading fungi. This paper provides a summary of the current global production of plastic and plastic waste accumulation in nature. A list is given of all the plastic-degrading fungi recorded thus far, based on the available literature, and comments are made relating to the major fungal groups. In addition, the phylogenetic relationships of plastic-degrading fungi were analyzed using a combined ITS, LSU, SSU, TEF, RPB1, and RPB2 dataset consisting of 395 strains. Our results confirm that plastic-degrading fungi are found in eleven classes in the fungal phyla Ascomycota (Dothideomycetes, Eurotiomycetes, Leotiomycetes, Saccharomycetes, and Sordariomycetes), Basidiomycota (Agaricomycetes, Microbotryomycetes, Tremellomycetes, Tritirachiomycetes, and Ustilaginomy-cetes), and Mucoromycota (Mucoromycetes). The taxonomic placement of plastic-degrading fungal taxa is briefly discussed. The Eurotiomycetes include the largest number of plastic degraders in the kingdom Fungi. The results presented herein are expected to influence the direction of future research on similar topics in order to find effective plastic-degrading fungi that can eliminate plastic wastes. The next publication of the series on plastic-degrading fungi will be focused on major metabolites, degradation pathways, and enzyme production in plastic degradation by fungi.

Can polymer-degrading microorganisms solve the bottleneck of plastics' environmental challenges?

Increasing world population and industrial activities have enhanced anthropogenic pollution, plastic pollution being especially alarming. So, plastics should be recycled and/or make them biodegradable. Chemical and physical remediating methods are usually energy consuming and costly. In addition, they are not ecofriendly and usually produce toxic byproducts. Bioremediation is a proper option as it is cost-efficient and environmentally friendly. Plastic production and consumption are increasing daily, and, as a consequence, more microorganisms are exposed to these nonbiodegradable polymers. Therefore, investigating new efficient microorganisms and increasing the knowledge about their biology can pave the way for efficient and feasible plastic bioremediation processes. In this sense, omics, systems biology and bioinformatics are three important fields to analyze the biodegradation pathways in microorganisms. Based on the above-mentioned technologies, researchers can engineer microorganisms with specific desired properties to make bioremediation more efficient.

Extracellular secretion of a cutinase with polyester-degrading potential by E. coli using a novel signal peptide from Amycolatopsis mediterranei

Recent studies in this laboratory showed that an extracellular cutinase from A. mediterranei (AmCut) was able to degrade the plastics polycaprolactone and polybutylene succinate. Such plastics can be slow to degrade in soils due to a lack of efficient polyester degrading organisms. AmCut also showed potential for the biocatalytic synthesis of esters by reverse hydrolysis. The gene for AmCut has an upstream leader sequence whose transcript is not present in the purified enzyme. In this study, we show using predictive modelling, that this sequence codes for an N-terminal signal peptide that directs transmembrane expression via the Sec secretion pathway. E. coli is a useful host for recombinant enzymes used in biocatalysis due to the ease of genetic manipulation in this organism, which allows tuning of enzymes for specific applications, by mutagenesis. When a truncated GST-tagged AmCut gene (lacking its signal peptide) was expressed in E. coli, all cutinase activity was observed in the cytosolic fraction. However, when GST-tagged AmCut was expressed in E. coli along with its native signal peptide, cutinase activity was observed in both the periplasmic space and the culture medium. This finding revealed that the native signal peptide of a Gram-positive organism (AmCut) was being recognised by the Gram-negative (E. coli) Sec transmembrane transport system. AmCut was transported into E. coli's periplasmic space from where it was released into the culture medium. Surprisingly, the presence of a bulky GST tag at the N-terminus of the signal peptide did not hinder transmembrane targeting. Although the periplasmic targeting was unexpected, it is not unprecedented due to the conservation of the Sec pathway across species. It was more surprising that AmCut was secreted from the periplasmic space into the culture medium. This suggests that extracellular AmCut translocation across the E. coli outer membrane may involve non-classical secretion pathways. This tuneable recombinant E. coli expressing extracellular AmCut may be useful for degradation of polyester substrates in the environment; this and other applications are discussed.

Expression and characterization of a novel lipase from Bacillus licheniformis NCU CS-5 for application in enhancing fatty acids flavor release for low-fat cheeses

A novel lipase from Bacillus licheniformis NCU CS-5 was expressed in different Escherichia coli cells. The recombinant enzyme achieved a high activity (161.74 U/mL) with protein concentration of 0.27 mg/mL under optimal conditions at the large-scale expression of 12 h. The recombinant lipase showed optimal activity at 40 ℃ and pH 10.0, and maintained more than 80% relative activity after 96 h of incubation at pH 9.0-10.0. This typical alkaline lipase was activated under medium temperature conditions (30 and 45 ℃ for 96 h). The lipase exhibited a degree of adaptability in various organic solvents and metal ions, and showed high specificity towards triglycerides with short and medium chain fatty acids. Among different substrates, the lipase showed the strongest binding affinity towards pNPP (Km = 0.674 mM, Vmax = 950.196 μM/min). In the experiments of its application in enhancing fatty acids flavor release for low-fat cheeses, the lipase was found to hydrolyze cheeses and mainly increase the contents of butyric acid, hexanoic acid, caprylic acid and decanoic acid. The results from NMR and GC provided the possibility of enhancing fatty acids flavor released from low-fat cheeses by the lipolysis method.

Bioprospecting of gut microflora for plastic biodegradation

The problem of plastic prevalence and associated pollution has grasped the entire planet drastically, putting all fields of science on the stake seeking remedies to this global havoc. To address this crisis, with a single remediation strategy is often found to be baseless, thereby much interest has been evoked in the development of multidisciplinary approaches - involving physico-chemical and biological strategies to nullify the aftermath of plastic pollution in all possible means. Even amidst, the availability of different approaches, the use of biological methods to combat plastic degradation has gained momentum. The most frequently used plastics appear in wide forms such as polyethylene plastic bags, polypropylene-based bottles, polyvinyl chloride pipes and polystyrene styrene cups. Plastic nicknamed as one of the toughest polymers viz. polycarbonate, acrylonitrile butadiene styrene (ABS) and Polydicyclopentadiene; quite often are called so as they resist degradation in normal environmental strategies. They are often degraded in non-hostile and harsh environments of pH, temperature, radiation etc. However, not always it is possible to create such harsh environments for plastic degradation. In such a scenario, the use of gut microbes that can withstand the harsh atmosphere of gut environment could serve as promising candidates for plastic biodegradation. The current article envisages the various gut microbes of various biological agents and their role in plastic remediation. The current review compiles the techniques available for plastic remediation, the microbial prospects of plastic remediation, its challenges, and possible breakthroughs to effective plastic remediation.

Phylogenetic analysis and in-depth characterization of functionally and structurally diverse CE5 cutinases

Cutinases are esterases that release fatty acids from the apoplastic layer in plants. As they accept bulky and hydrophobic substrates, cutinases could be used in many applications, ranging from valorization of bark-rich side streams to plastic recycling. Advancement of these applications, however, requires deeper knowledge of cutinases' biodiversity and structure-function relationships. Here, we mined over 3000 members from carbohydrate esterase family 5 for putative cutinases and condensed it to 151 genes from known or putative lignocellulose-targeting organisms. The 151 genes were subjected to a phylogenetic analysis, which showed that cutinases with available crystal structures were phylogenetically closely related. We then selected nine phylogenic diverse cutinases for recombinant production and characterized their kinetic activity against para-nitrophenol substrates esterified with consecutively longer alkyl chains (pNP-C2 to C16). Each investigated cutinase had a unique activity fingerprint against the tested pNP substrates. The five enzymes with the highest activity on pNP-C12 and C16, indicative of activity on bulky hydrophobic compounds, were selected for in-depth kinetic and structure-function analysis. All five enzymes showed a decrease in kcat values with increasing substrate chain length, whereas KM values and binding energies (calculated from in silico docking analysis) improved. Two cutinases from Fusarium solani and Cryptococcus sp. exhibited outstandingly low KM values, resulting in high catalytic efficiencies toward pNP-C16. Docking analysis suggested that different clades of the phylogenetic tree may harbor enzymes with different modes of substrate interaction, involving a solvent-exposed catalytic triad, a lipase-like lid, or a clamshell-like active site possibly formed by flexible loops.

A Novel Actinobacterial Cutinase Containing a Non-Catalytic Polymer-Binding Domain

The single putative cutinase-encoding gene from the genome of Kineococcus radiotolerans SRS30216 was cloned and expressed in Escherichia coli as a secreted fusion protein, designated YebF-KrCUT, where YebF is the extracellular carrier protein. The 294-amino acid sequence of KrCUT is unique among currently characterized cutinases by having a C-terminal extension that consists of a short (Pro-Thr)-rich linker and a 55-amino-acid region resembling the substrate binding domain of poly(hydroxybutyrate) (PHB) depolymerases. Phylogenetically, KrCUT takes a unique position among known cutinases and cutinase-like proteins of bacterial and fungal origin. A modeled structure of KrCUT, although displaying a typical α/ß hydrolase fold, shows some unique loops close to the catalytic site. The 39-kDa YebF-KrCUT fusion protein and a truncated variant thereof were purified to electrophoretic homogeneity and functionally characterized. The melting temperatures (T_m) of KrCUT and its variant KrCUT206 devoid of the putative PHB-binding domain were established to be very similar at 50-51°C. Cutinase activity was confirmed by the appearance of characteristic cutin components, C₁₆ and C₁₈ hydroxyl fatty acids, in the mass chromatograms following incubation of KrCUT with apple cutin as substrate. KrCUT also efficiently degraded synthetic polyesters such as polycaprolactone and poly(1,3-propylene adipate). Although incapable of PHB depolymerization, KrCUT could efficiently bind PHB, confirming the predicted characteristic of the C-terminal region. KrCUT also potentiated the activity of pectate lyase in the degradation of pectin from hemp fibres. This synergistic effect is relevant to the enzyme retting process of natural fibres. IMPORTANCE. To date only a limited number of cutinases have been isolated and characterized from nature, the majority being sourced from phytopathogenic fungi and thermophilic bacteria. The significance of our research relates to the identification and characterization of a unique member of microbial cutinases, of name KrCUT, that was derived from the genome of the Gram-positive Kineococcus radiotolerans SRS30216, a highly radiation-resistant actinobacterium. Given the wide-ranging importance of cutinases in applications such as the degradation of natural and synthetic polymers, in the textile industry, in laundry detergents, or in biocatalysis (e.g., transesterification reactions), our results could foster new research leading to broader biotechnological impacts. This study also demonstrated that genome mining or prospecting is a viable means to discover novel biocatalysts as environmentally friendly and biotechnological tool.

Accessory enzymes of hypercellulolytic Penicillium funiculosum facilitate complete saccharification of sugarcane bagasse

BACKGROUND

Sugarcane bagasse (SCB) is an abundant feedstock for second-generation bioethanol production. This complex biomass requires an array of carbohydrate active enzymes (CAZymes), mostly from filamentous fungi, for its deconstruction to monomeric sugars for the production of value-added fuels and chemicals. In this study, we evaluated the repertoire of proteins in the secretome of a catabolite repressor-deficient strain of Penicillium funiculosum, PfMig1⁸⁸, in response to SCB induction and examined their role in the saccharification of SCB.

RESULTS

A systematic approach was developed for the cultivation of the fungus with the aim of producing and understanding arrays of enzymes tailored for saccharification of SCB. To achieve this, the fungus was grown in media supplemented with different concentrations of pretreated SCB (0-45 g/L). The profile of secreted proteins was characterized by enzyme activity assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 280 proteins were identified in the secretome of PfMig1⁸⁸, 46% of them being clearly identified as CAZymes. Modulation of the cultivation media with SCB up to 15 g/L led to sequential enhancement in the secretion of hemicellulases and cell wall-modifying enzymes, including endo-β-1,3(4)-glucanase (GH16), endo-α-1,3-glucanase (GH71), xylanase (GH30), β-xylosidase (GH5), β-1,3-galactosidase (GH43) and cutinase (CE5). There was ~ 122% and 60% increases in β-xylosidase and cutinase activities, respectively. There was also a 36% increase in activities towards mixed-linked glucans. Induction of these enzymes in the secretome improved the saccharification performance to 98% (~ 20% increase over control), suggesting their synergy with core cellulases in accessing the recalcitrant region of SCB.

CONCLUSION

Our findings provide an insight into the enzyme system of PfMig1⁸⁸ for degradation of complex biomass such as SCB and highlight the importance of adding SCB to the culture medium to optimize the secretion of enzymes specific for the saccharification of sugarcane bagasse.

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

OBJECTIVES

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

RESULTS

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

CONCLUSIONS

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

Discovery and development of a novel short-chain fatty acid ester synthetic biocatalyst under aqueous phase from Monascus purpureus isolated from Baijiu

Short-chain fatty acid esters are important flavor chemicals in Chinese traditional fermented Baijiu. Monascus purpureus was recognized as an important microorganism contributing to ester synthesis. However, the molecular basis for ester synthesis was still lacking. The present work combined genome sequencing, transcriptome sequencing, gene library construction, and enzyme engineering to discover a novel catalyst from M. purpureus (isolated from Baijiu fermentation starter). Enzyme LIP05, belonging to the α/β hydrolase family, was identified to synthesize short-chain fatty acid esters under aqueous phase. After deleting the lid domain of LIP05, the synthesis of ethyl pentanoate, ethyl hexanoate, ethyl octanoate, or ethyl decanoate was achieved. Ethyl octanoate with the highest conversion ratio of 93.7% was obtained with the assistance of ultrasound. The study reveals the molecular basis for synthesizing short-chain fatty acid esters by M. purpureus and will promote the application of the species or the enzyme in food industry.

Synthesis of flavor esters by a novel lipase from Aspergillus niger in a soybean-solvent system

To find a lipase for synthesis of flavor esters in food processing, a total of 35 putative lipases from Aspergillus niger F0215 were heterologously expressed and their esterification properties in crude preparations were examined. One of them, named An-lipase with the highest esterification rate (23.1%) was selected for further study. The purified An-lipase had the maximal activity at 20 °C and pH 6.5 and the specific activity of 1293 U/mg. Sixty percent of the activity was maintained in a range of temperatures of 0-30 °C and pHs of 3.0-8.5. The highest hydrolysis activity of An-lipase was towards pNPC (C8), followed by pNPB (C4) and pNPA (C2), then pNPL (C12). K _m, V _max, k _cat, and k _cat/K _m towards pNPC were 26.7 mmol/L, 129.9 mmol/(L h), 23.2 s^-1, and 0.8/mM/s, respectively. The ethyl lactate, butyl butyrate, and ethyl caprylate flavor esters were produced by esterification of the corresponding acids with conversion efficiencies of 15.8, 37.5, and 24.7%, respectively, in a soybean-oil-based solvent system. In conclusion, An lipase identified in this study significantly mediated synthesis of predominant flavor esters (ethyl lactate, butyl butyrate, and ethyl caprylate) in a soybean-oil-lacking other toxic organic solvents, which has potential application in food industries.

A Middle-Aged Enzyme Still in Its Prime: Recent Advances in the Field of Cutinases

Cutinases are α/β hydrolases, and their role in nature is the degradation of cutin. Such enzymes are usually produced by phytopathogenic microorganisms in order to penetrate their hosts. The first focused studies on cutinases started around 50 years ago. Since then, numerous cutinases have been isolated and characterized, aiming at the elucidation of their structure–function relations. Our deeper understanding of cutinases determines the applications by which they could be utilized; from food processing and detergents, to ester synthesis and polymerizations. However, cutinases are mainly efficient in the degradation of polyesters, a natural function. Therefore, these enzymes have been successfully applied for the biodegradation of plastics, as well as for the delicate superficial hydrolysis of polymeric materials prior to their functionalization. Even though research on this family of enzymes essentially began five decades ago, they are still involved in many reports; novel enzymes are being discovered, and new fields of applications arise, leading to numerous related publications per year. Perhaps the future of cutinases lies in their evolved descendants, such as polyesterases, and particularly PETases. The present article reviews the biochemical and structural characteristics of cutinases and cutinase-like hydrolases, and their applications in the field of bioremediation and biocatalysis.

Metabolic engineering of Clostridium acetobutylicum for the production of butyl butyrate

Butyl butyrate is widely used as a fragrance additive for foods and beverages. The first step in the currently used process is the production of precursors, including butanol and butyrate, from petroleum using chemical catalysts, followed by the conversion of precursors to butyl butyrate by immobilized lipase. In this work, we engineered Clostridium acetobutylicum for the selective, one-step production of butyl butyrate from glucose. C. acetobutylicum ATCC 824, possessing a strong carbon flux that yields butanol and butyryl-CoA, was selected as a host and was engineered by introducing alcohol acyltransferases (AATs) from Fragaria x ananassa (strawberry) or Malus sp. (apple). Batch culture of the engineered C. acetobutylicum strain CaSAAT expressing the strawberry SAAT gene produced 50.07 mg/L of butyl butyrate with a selectivity of 84.8% of total esters produced. Also, the engineered C. acetobutylicum strain CaAAAT expressing the apple AAAT gene produced 40.60 mg/L of butyl butyrate with a selectivity of 87.4%. This study demonstrated the feasibility of the one-step fermentation of butyl butyrate from glucose in the engineered C. acetobutylicum, as a proof of concept.

Combined genome and transcriptome sequencing to investigate the plant cell wall degrading enzyme system in the thermophilic fungus Malbranchea cinnamomea

BACKGROUND

Genome and transcriptome sequencing has greatly facilitated the understanding of biomass-degrading mechanisms in a number of fungal species. The information obtained enables the investigation and discovery of genes encoding proteins involved in plant cell wall degradation, which are crucial for saccharification of lignocellulosic biomass in second-generation biorefinery applications. The thermophilic fungus Malbranchea cinnamomea is an efficient producer of many industrially relevant enzymes and a detailed analysis of its genomic content will considerably enhance our understanding of its lignocellulolytic system and promote the discovery of novel proteins.

RESULTS

The 25-million-base-pair genome of M. cinnamomea FCH 10.5 was sequenced with 225× coverage. A total of 9437 protein-coding genes were predicted and annotated, among which 301 carbohydrate-active enzyme (CAZyme) domains were found. The putative CAZymes of M. cinnamomea cover cellulases, hemicellulases, chitinases and pectinases, equipping the fungus with the ability to grow on a wide variety of biomass types. Upregulation of 438 and 150 genes during growth on wheat bran and xylan, respectively, in comparison to growth on glucose was revealed. Among the most highly upregulated CAZymes on xylan were glycoside hydrolase family GH10 and GH11 xylanases, as well as a putative glucuronoyl esterase and a putative lytic polysaccharide monooxygenase (LPMO). AA9-domain-containing proteins were also found to be upregulated on wheat bran, as well as a putative cutinase and a protein harbouring a CBM9 domain. Several genes encoding secreted proteins of unknown function were also more abundant on wheat bran and xylan than on glucose.

CONCLUSIONS

The comprehensive combined genome and transcriptome analysis of M. cinnamomea provides a detailed insight into its response to growth on different types of biomass. In addition, the study facilitates the further exploration and exploitation of the repertoire of industrially relevant lignocellulolytic enzymes of this fungus.