Impact of surface delignification on fire retardancy of wood treated with polyelectrolyte complexes.

Wood is a natural composite widely employed as a residential building interior finishing. Although wood is readily available and offers benefits to the occupants, such as enhanced well-being, it is rarely employed in commercial construction due, amongst others, to the potential hazard of fire propagation. The application of flame retardant (FR) treatments leads to a reduction of wood flammability and supports wood as interior finishing. Polyelectrolyte complexes (PECs) deposition is an innovative surface treatment that has already proven its efficiency for fabrics. For wood, recent studies have highlighted that the weight gain impacted the fire-retardancy, and a minimum of 2 wt.-% was set to obtain fire protection. This study explored the potential of surface delignification to activate the wood surface and facilitate the PEC impregnation. Yellow birch (Betula alleghaniensis, Britt.) was surface delignified (0.3 mm) using sodium chlorite. The treatment impact on wood was evaluated by spectroscopy analysis (FTIR, Raman), and the increase in wood wettability was demonstrated (contact angle decreases from 50° to 35° after the surface delignification). Then, PECs consisting of polyethyleneimine and sodium phytate were surface impregnated in wood and delignified wood. The flame retardancy was evaluated using a cone calorimeter. Despite the increase in weight gain (1.5 wt.-% ± 0.3 wt.-% to 4.3 wt.-% ± 2.5 wt.-%), fire performance was not improved. This study demonstrates that lignin strongly affects char formation, even in the presence of PECs.

Enzymes' Power for Plastics Degradation.

Plastics are everywhere in our modern way of living, and their production keeps increasing every year, causing major environmental concerns. Nowadays, the end-of-life management involves accumulation in landfills, incineration, and recycling to a lower extent. This ecological threat to the environment is inspiring alternative bio-based solutions for plastic waste treatment and recycling toward a circular economy. Over the past decade, considerable efforts have been made to degrade commodity plastics using biocatalytic approaches. Here, we provide a comprehensive review on the recent advances in enzyme-based biocatalysis and in the design of related biocatalytic processes to recycle or upcycle commodity plastics, including polyesters, polyamides, polyurethanes, and polyolefins. We also discuss scope and limitations, challenges, and opportunities of this field of research. An important message from this review is that polymer-assimilating enzymes are very likely part of the solution to reaching a circular plastic economy.

An NMR look at an engineered PET depolymerase.

Plastic environmental pollution is a major issue that our generation must face to protect our planet. Plastic recycling has the potential not only to reduce the pollution but also to limit the need for fossil-fuel-based production of new plastics. Enzymes capable of breaking down plastic could thereby support such a circular economy. Polyethylene terephthalate (PET) degrading enzymes have recently attracted considerable interest and have been subjected to intensive enzyme engineering to improve their characteristics. A quadruple mutant of Leaf-branch Compost Cutinase (LCC) was identified as a most efficient and promising enzyme. Here, we use NMR to follow the initial LCC enzyme through its different mutations that lead to its improved performance. We experimentally define the two calcium-binding sites and show their importance on the all-or-nothing thermal unfolding process, which occurs at a temperature of 72°C close to the PET glass transition temperature. Using various NMR probes such as backbone amide, methyl group, and histidine side-chain resonances, we probe the interaction of the enzymes with mono-(2-hydroxyethyl)terephthalic acid. The latter experiments are interpreted in terms of accessibility of the active site to the polymer chain.

Characterization of a novel ß-alanine biosynthetic pathway consisting of promiscuous metabolic enzymes.

Bacteria adapt to utilize the nutrients available in their environment through a sophisticated metabolic system composed of highly specialized enzymes. Although these enzymes can metabolize molecules other than those for which they evolved, their efficiency toward promiscuous substrates is considered too low to be of physiological relevance. Herein, we investigated the possibility that these promiscuous enzymes are actually efficient enough at metabolizing secondary substrates to modify the phenotype of the cell. For example, in the bacterium Acinetobacter baylyi ADP1 (ADP1), panD (coding for l-aspartate decarboxylase) encodes the only protein known to catalyze the synthesis of ß-alanine, an obligate intermediate in CoA synthesis. However, we show that the ADP1 ΔpanD mutant could also form this molecule through an unknown metabolic pathway arising from promiscuous enzymes and grow as efficiently as the wildtype strain. Using metabolomic analyses, we identified 1,3-diaminopropane and 3-aminopropanal as intermediates in this novel pathway. We also conducted activity screening and enzyme kinetics to elucidate candidate enzymes involved in this pathway, including 2,4-diaminobutyrate aminotransferase (Dat) and 2,4-diaminobutyrate decarboxylase (Ddc) and validated this pathway in vivo by analyzing the phenotype of mutant bacterial strains. Finally, we experimentally demonstrate that this novel metabolic route is not restricted to ADP1. We propose that the occurrence of conserved genes in hundreds of genomes across many phyla suggests that this previously undescribed pathway is widespread in prokaryotes.

Innovative Polyelectrolyte Treatment to Flame-Retard Wood.

Fire protection has been a major challenge in wood construction for many years, mainly due to the high flame spread risk associated with wood flooring. Wood fire-retardancy is framed by two main axes: coating and bulk impregnation. There is a growing need for economically and environmentally friendly alternatives. The study of polyelectrolyte complexes (PECs) for wood substrates is in its infancy, but PECs' versatility and eco-friendly character are already recognized for fabric fire-retardancy fabrics. In this study, a new approach to PEC characterization is proposed. First, PECs, which consist of polyethyleneimine and sodium phytate, were chemically and thermally characterized to select the most promising systems. Then, yellow birch (Betula alleghaniensis Britt.) was surface-impregnated under reduced pressure with the two PECs identified as the best options. Overall, wood fire-retardancy was improved with a low weight gain of 2 wt.% without increasing water uptake.

Phenotype description in KIF5C gene hot-spot mutations responsible for malformations of cortical development (MCD).

Malformations of cortical development (MCD) represent a large group of brain cortical anomalies characterized by distinctive MRI findings. This 'radiologically-based' classification required re evaluation over time on identified underlying mechanisms (cytogenetic and/or molecular). The understanding of genotype findings (nature of cytogenetic/molecular mutation, cellular pathways consequences, timing, …) draw line of evidence on these distinctive group of conditions whereas sometimes precise and constant recurrent genotype/phenotype correlation may not be present. The clinical diagnosis of MCD is often difficult due to variability and rarity of individual types of malformations. Recent studies have established a relationship between lissencephaly and pathogenic variants in genes involved in the kinesin/tubulin pathways, as the KIF5C gene. Pathogenic variants in the KIF5C gene are a more recently discovered cause of severe developmental delay with epilepsy, characterized by specific malformation of cortical development such as pachygyria. Only seven children have been described to date. We report the natural history of a sixteen years old patient identified carrier of a KIF5C gene mutation who developed infantile epilepsy. We then gather phenotype description and molecular results of all reported patients so far in order to better define this entity.

An artificial chromosome ylAC enables efficient assembly of multiple genes in Yarrowia lipolytica for biomanufacturing.

The efficient use of the yeast Yarrowia lipolytica as a cell factory is hampered by the lack of powerful genetic engineering tools dedicated for the assembly of large DNA fragments and the robust expression of multiple genes. Here we describe the design and construction of artificial chromosomes (ylAC) that allow easy and efficient assembly of genes and chromosomal elements. We show that metabolic pathways can be rapidly constructed by various assembly of multiple genes in vivo into a complete, independent and linear supplementary chromosome with a yield over 90%. Additionally, our results reveal that ylAC can be genetically maintained over multiple generations either under selective conditions or, without selective pressure, using an essential gene as the selection marker. Overall, the ylACs reported herein are game-changing technology for Y. lipolytica, opening myriad possibilities, including enzyme screening, genome studies and the use of this yeast as a previous unutilized bio-manufacturing platform.

Lipases: An Overview.

Lipases are ubiquitous enzymes, widespread in nature. They were first isolated from bacteria in the early nineteenth century, and the associated research continuously increased due to the characteristics of these enzymes. This chapter reviews the main sources, structural properties, and industrial applications of these highly studied enzymes.

Developing cellulolytic Yarrowia lipolytica as a platform for the production of valuable products in consolidated bioprocessing of cellulose.

BACKGROUND: Both industrial biotechnology and the use of cellulosic biomass as feedstock for the manufacture of various commercial goods are prominent features of the bioeconomy. In previous work, with the aim of developing a consolidated bioprocess for cellulose bioconversion, we conferred cellulolytic activity of Yarrowia lipolytica, one of the most widely studied "nonconventional" oleaginous yeast species. However, further engineering this strain often leads to the loss of previously introduced heterologous genes due to the presence of multiple LoxP sites when using Cre-recombinase to remove previously employed selection markers. RESULTS: In the present study, we first optimized the strategy of expression of multiple cellulases and rescued selection makers to obtain an auxotrophic cellulolytic Y. lipolytica strain. Then we pursued the quest, exemplifying how this cellulolytic Y. lipolytica strain can be used as a CBP platform for the production of target products. Our results reveal that overexpression of SCD1 gene, encoding stearoyl-CoA desaturase, and DGA1, encoding acyl-CoA:diacylglycerol acyltransferase, confers the obese phenotype to the cellulolytic Y. lipolytica. When grown in batch conditions and minimal medium, the resulting strain consumed 12 g/L cellulose and accumulated 14% (dry cell weight) lipids. Further enhancement of lipid production was achieved either by the addition of glucose or by enhancing cellulose consumption using a commercial cellulase cocktail. Regarding the latter option, although the addition of external cellulases is contrary to the concept of CBP, the amount of commercial cocktail used remained 50% lower than that used in a conventional process (i.e., without internalized production of cellulases). The introduction of the LIP2 gene into cellulolytic Y. lipolytica led to the production of a strain capable of producing lipase 2 while growing on cellulose. Remarkably, when the strain was grown on glucose, the expression of six cellulases did not alter the level of lipase production. When grown in batch conditions on cellulose, the engineered strain consumed 16 g/L cellulose and produced 9.0 U/mL lipase over a 96-h period. The lipase yield was 562 U lipase/g cellulose, which represents 60% of that obtained on glucose. Finally, expression of the hydroxylase from Claviceps purpurea (CpFAH12) in cellulolytic Y. lipolytica procured a strain that can produce ricinoleic acid (RA). Using this strain in batch cultures revealed that the consumption of 11 g/L cellulose sustained the production of 2.2 g/L RA in the decane phase, 69% of what was obtained on glucose. CONCLUSIONS: In summary, this study has further demonstrated the potential of cellulolytic Y. lipolytica as a microbial platform for the bioconversion of cellulose into target products. Its ability to be used in consolidated process designs has been exemplified and clues revealing how cellulose consumption can be further enhanced using commercial cellulolytic cocktails are provided.

Discovery of carbamate degrading enzymes by functional metagenomics.

Bioremediation of pollutants is a major concern worldwide, leading to the research of new processes to break down and recycle xenobiotics and environment contaminating polymers. Among them, carbamates have a very broad spectrum of uses, such as toxinogenic pesticides or elastomers. In this study, we mined the bovine rumen microbiome for carbamate degrading enzymes. We isolated 26 hit clones exhibiting esterase activity, and were able to degrade at least one of the targeted polyurethane and pesticide carbamate compounds. The most active clone was deeply characterized. In addition to Impranil, this clone was active on Tween 20, pNP-acetate, butyrate and palmitate, and on the insecticide fenobucarb. Sequencing and sub-cloning of the best target revealed a novel carboxyl-ester hydrolase belonging to the lipolytic family IV, named CE_Ubrb. This study highlights the potential of highly diverse microbiota such as the ruminal one for the discovery of promiscuous enzymes, whose versatility could be exploited for industrial uses.

Expressing accessory proteins in cellulolytic Yarrowia lipolytica to improve the conversion yield of recalcitrant cellulose.

BACKGROUND: A recently constructed cellulolytic Yarrowia lipolytica is able to grow efficiently on an industrial organosolv cellulose pulp, but shows limited ability to degrade crystalline cellulose. In this work, we have further engineered this strain, adding accessory proteins xylanase II (XYNII), lytic polysaccharide monooxygenase (LPMO), and swollenin (SWO) from Trichoderma reesei in order to enhance the degradation of recalcitrant substrate. RESULTS: The production of EG I was enhanced using a promoter engineering strategy. This provided a new cellulolytic Y. lipolytica strain, which compared to the parent strain, exhibited higher hydrolytic activity on different cellulosic substrates. Furthermore, three accessory proteins, TrXYNII, TrLPMOA and TrSWO, were individually expressed in cellulolytic and non-cellulolytic Y. lipolytica. The amount of rhTrXYNII and rhTrLPMOA secreted by non-cellulolytic Y. lipolytica in YTD medium during batch cultivation in flasks was approximately 62 and 52 mg/L, respectively. The purified rhTrXYNII showed a specific activity of 532 U/mg-protein on beechwood xylan, while rhTrLPMOA exhibited a specific activity of 14.4 U/g-protein when using the Amplex Red/horseradish peroxidase assay. Characterization of rhTrLPMOA revealed that this protein displays broad specificity against ß-(1,4)-linked glucans, but is inactive on xylan. Further studies showed that the presence of TrLPMOA synergistically enhanced enzymatic hydrolysis of cellulose by cellulases, while TrSWO1 boosted cellulose hydrolysis only when it was applied before the action of cellulases. The presence of rTrXYNII enhanced enzymatic hydrolysis of an industrial cellulose pulp and of wheat straw. Co-expressing TrXYNII and TrLPMOA in cellulolytic Y. lipolytica with enhanced EG I production procured a novel engineered Y. lipolytica strain that displayed enhanced ability to degrade both amorphous (CIMV-cellulose) and recalcitrant crystalline cellulose in complex biomass (wheat straw) by 16 and 90%, respectively. CONCLUSIONS: This study has provided a potent cellulose-degrading Y. lipolytica strain that co-expresses a core set of cellulolytic enzymes and some accessory proteins. Results reveal that the tuning of cellulase production and the production of accessory proteins leads to optimized performance. Accordingly, the beneficial effect of accessory proteins for cellulase-mediated degradation of cellulose is underlined, especially when crystalline cellulose and complex biomass are used as substrates. Findings specifically underline the benefits and specific properties of swollenin. Although in our study swollenin clearly promoted cellulase action, its use requires process redesign to accommodate its specific mode of action.

Modelling Behaviour of a Carbon Epoxy Composite Exposed to Fire: Part II-Comparison with Experimental Results.

Based on a phenomenological methodology, a three dimensional (3D) thermochemical model was developed to predict the temperature profile, the mass loss and the decomposition front of a carbon-reinforced epoxy composite laminate (T700/M21 composite) exposed to fire conditions. This 3D model takes into account the energy accumulation by the solid material, the anisotropic heat conduction, the thermal decomposition of the material, the gas mass flow into the composite, and the internal pressure. Thermophysical properties defined as temperature dependant properties were characterised using existing as well as innovative methodologies in order to use them as inputs into our physical model. The 3D thermochemical model accurately predicts the measured mass loss and observed decomposition front when the carbon fibre/epoxy composite is directly impacted by a propane flame. In short, the model shows its capability to predict the fire behaviour of a carbon fibre reinforced composite for fire safety engineering.

Modelling Behaviour of a Carbon Epoxy Composite Exposed to Fire: Part I-Characterisation of Thermophysical Properties.

Thermophysical properties of a carbon-reinforced epoxy composite laminate (T700/M21 composite for aircraft structures) were evaluated using different innovative characterisation methods. Thermogravimetric Analysis (TGA), Simultaneous Thermal analysis (STA), Laser Flash analysis (LFA), and Fourier Transform Infrared (FTIR) analysis were used for measuring the thermal decomposition, the specific heat capacity, the anisotropic thermal conductivity of the composite, the heats of decomposition and the specific heat capacity of released gases. It permits to get input data to feed a three-dimensional (3D) model given the temperature profile and the mass loss obtained during well-defined fire scenarios (model presented in Part II of this paper). The measurements were optimised to get accurate data. The data also permit to create a public database on an aeronautical carbon fibre/epoxy composite for fire safety engineering.

Conferring cellulose-degrading ability to Yarrowia lipolytica to facilitate a consolidated bioprocessing approach.

BACKGROUND: Yarrowia lipolytica, one of the most widely studied "nonconventional" oleaginous yeast species, is unable to grow on cellulose. Recently, we identified and overexpressed two endogenous ß-glucosidases in Y. lipolytica, thus enabling this yeast to use cello-oligosaccharides as a carbon source for growth. Using this engineered yeast platform, we have now gone further toward building a fully cellulolytic Y. lipolytica for use in consolidated bioprocessing of cellulose. RESULTS: Initially, different essential enzyme components of a cellulase cocktail (i.e,. cellobiohydrolases and endoglucanases) were individually expressed in Y. lipolytica in order to ascertain the viability of the strategy. Accordingly, the Trichoderma reesei endoglucanase I (TrEG I) and II (TrEG II) were secreted as active proteins in Y. lipolytica, with the secretion yield of EG II being twice that of EG I. Characterization of the purified His-tagged recombinant EG proteins (rhTrEGs) revealed that rhTrEG I displayed higher specific activity than rhTrEG II on both cellotriose and insoluble cellulosic substrates, such as Avicel, ß-1, 3 glucan, ß-1, 4 glucan, and PASC. Similarly, cellobiohydrolases, such as T. reesei CBH I and II (TrCBH I and II), and the CBH I from Neurospora crassa (NcCBH I) were successfully expressed in Y. lipolytica. However, the yield of the expressed TrCBH I was low, so work on this was not pursued. Contrastingly, rhNcCBH I was not only well expressed, but also highly active on PASC and more active on Avicel (0.11 U/mg) than wild-type TrCBH I (0.065 U/mg). Therefore, work was pursued using a combination of NcCBH I and TrCBH II. The quantification of enzyme levels in culture supernatants revealed that the use of a hybrid promoter instead of the primarily used TEF promoter procured four and eight times more NcCBH I and TrCBH II expressions, respectively. Finally, the coexpression of the previously described Y. lipolytica ß-glucosidases, the CBH II, and EG I and II from T. reesei, and the N. crassa CBH I procured an engineered Y. lipolytica strain that was able to grow both on model cellulose substrates, such as highly crystalline Avicel, and on industrial cellulose pulp, such as that obtained using an organosolv process. CONCLUSIONS: A Y. lipolytica strain coexpressing six cellulolytic enzyme components has been successfully developed. In addition, the results presented show how the recombinant strain can be optimized, for example, using artificial promoters to tailor expression levels. Most significantly, this study has provided a demonstration of how the strain can grow on a sample of industrial cellulose as sole carbon source, thus revealing the feasibility of Yarrowia-based consolidated bioprocess for the production of fuel and chemical precursors. Further, enzyme and strain optimization, coupled to appropriate process design, will undoubtedly lead to much better performances in the future.

Metagenomics for the discovery of pollutant degrading enzymes.

Organic pollutants, including xenobiotics, are often persistent and toxic organic compounds resulting from human activities and released in large amounts into terrestrial, fluvial and marine environments. However, some microbial species which are naturally exposed to these compounds in their own habitat are capable of degrading a large range of pollutants, especially poly-aromatic, halogenated and polyester molecules. These microbes constitute a huge reservoir of enzymes for the diagnosis of pollution and for bioremediation. Most are found in highly complex ecosystems like soils, activated sludge, compost or polluted water, and more than 99% have never been cultured. Meta-omic approaches are thus well suited to retrieve biocatalysts from these environmental samples. In this review, we report the latest advances in functional metagenomics aimed at the discovery of enzymes capable of acting on different kinds of polluting molecules.

Development of cellobiose-degrading ability in Yarrowia lipolytica strain by overexpression of endogenous genes.

BACKGROUND: Yarrowia lipolytica, one of the most widely studied "nonconventional" oleaginous yeast species, is unable to grow on cellobiose. Engineering cellobiose-degrading ability into this yeast is a vital step towards the development of cellulolytic biocatalysts suitable for consolidated bioprocessing. RESULTS: In the present work, we identified six genes encoding putative ß-glucosidases in the Y. lipolytica genome. To study these, homologous expression was attempted in Y. lipolytica JMY1212 Zeta. Two strains overexpressing BGL1 (YALI0F16027g) and BGL2 (YALI0B14289g) produced ß-glucosidase activity and were able to degrade cellobiose, while the other four did not display any detectable activity. The two active ß-glucosidases, one of which was mainly cell-associated while the other was present in the extracellular medium, were purified and characterized. The two Bgls were most active at 40-45°C and pH 4.0-4.5, and exhibited hydrolytic activity on various ß-glycoside substrates. Specifically, Bgl1 displayed 12.5-fold higher catalytic efficiency on cellobiose than Bgl2. Significantly, in experiments where cellobiose or cellulose (performed in the presence of a ß-glucosidase-deficient commercial cellulase cocktail produced by Trichoderma reseei) was used as carbon source for aerobic cultivation, Y. lipolytica ∆pox co-expressing BGL1 and BGL2 grew better than the Y. lipolytica strains expressing single BGLs. The specific growth rate and biomass yield of Y. lipolytica JMY1212 co-expressing BGL1 and BGL2 were 0.15 h(-1) and 0.50 g-DCW/g-cellobiose, respectively, similar to that of the control grown on glucose. CONCLUSIONS: We conclude that the bi-functional Y. lipolytica developed in the current study represents a vital step towards the creation of a cellulolytic yeast strain that can be used for lipid production from lignocellulosic biomass. When used in combination with commercial cellulolytic cocktails, this strain will no doubt reduce enzyme requirements and thus costs.

The Effects of Thermophysical Properties and Environmental Conditions on Fire Performance of Intumescent Coatings on Glass Fibre-Reinforced Epoxy Composites.

Intumescent coatings are commonly used as passive fire protection systems for steel structures. The purpose of this work is to explore whether these can also be used effectively on glass fibre-reinforced epoxy (GRE) composites, considering the flammability of the composites compared to non-flammable steel substrate. The thermal barrier and reaction-to-fire properties of three commercial intumescent coatings on GRE composites have been studied using a cone calorimeter. Their thermophysical properties in terms of heating rate and/or temperature dependent char expansion ratios and thermal conductivities have been measured and correlated. It has been suggested that these two parameters can be used to design coatings to protect composite laminates of defined thicknesses for specified periods of time. The durability of the coatings to water absorption, peeling, impact, and flexural loading were also studied. A strong adhesion between all types of coatings and the substrate was observed. Water soaking had a little effect on the fire performance of epoxy based coatings. All types of 1 mm thick coatings on GRE helped in retaining ~90% of the flexural property after 2 min exposure to 50 kW/m² heat flux whereas the uncoated laminate underwent severe delamination and loss in structural integrity after 1 min.

Characterization of Thermo-Physical Properties of EVA/ATH: Application to Gasification Experiments and Pyrolysis Modeling.

The pyrolysis of solid polymeric materials is a complex process that involves both chemical and physical phenomena such as phase transitions, chemical reactions, heat transfer, and mass transport of gaseous components. For modeling purposes, it is important to characterize and to quantify the properties driving those phenomena, especially in the case of flame-retarded materials. In this study, protocols have been developed to characterize the thermal conductivity and the heat capacity of an ethylene-vinyl acetate copolymer (EVA) flame retarded with aluminum tri-hydroxide (ATH). These properties were measured for the various species identified across the decomposition of the material. Namely, the thermal conductivity was found to decrease as a function of temperature before decomposition whereas the ceramic residue obtained after the decomposition at the steady state exhibits a thermal conductivity as low as 0.2 W/m/K. The heat capacity of the material was also investigated using both isothermal modulated Differential Scanning Calorimetry (DSC) and the standard method (ASTM E1269). It was shown that the final residue exhibits a similar behavior to alumina, which is consistent with the decomposition pathway of EVA/ATH. Besides, the two experimental approaches give similar results over the whole range of temperatures. Moreover, the optical properties before decomposition and the heat capacity of the decomposition gases were also analyzed. Those properties were then used as input data for a pyrolysis model in order to predict gasification experiments. Mass losses of gasification experiments were well predicted, thus validating the characterization of the thermo-physical properties of the material.

Construction of a highly active xylanase displaying oleaginous yeast: comparison of anchoring systems.

Three Yarrowia lipolytica cell wall proteins (YlPir, YlCWP1 and YlCBM) were evaluated for their ability to display the xylanase TxXYN from Thermobacillus xylanilyticus on the cell surface of Y. lipolytica. The fusion proteins were produced in Y. lipolytica JMY1212, a strain engineered for mono-copy chromosomal insertion, and enabling accurate comparison of anchoring systems. The construction using YlPir enabled cell bound xylanase activity to be maximised (71.6 U/g). Although 48% of the activity was released in the supernatant, probably due to proteolysis at the fusion zone, this system is three times more efficient for the anchoring of TxXYN than the YlCWP1 system formerly developed for Y. lipolytica. As far as we know it represents the best displayed xylanase activity ever published. It could be an attractive alternative anchoring system to display enzymes in Y. lipolytica.

Yarrowia lipolytica lipase Lip2: an efficient enzyme for the production of concentrates of docosahexaenoic acid ethyl ester.

The production of Omega-3 (ω-3) polyunsaturated fatty acids (PUFAs) rich in cis-4,7,10,13,16,19-docosahexaenoic acid (DHA) was studied using lipase-catalysed hydrolysis of a mixture of ethyl esters from tuna oil. Lipases from Yarrowia lipolytica (YLL2), Thermomyces lanuginosus (TLL) and Candida rugosa (CRL1, CRL3 and CRL4) were tested. C. rugosa lipases discriminated esters on the basis of their chain length, with less affinity for γ-linolenate, 11-eicosenoate, arachidonate, EPA, DPA and DHA ethyl esters. However, YLL2 and TLL improved discrimination towards DHA, as enzyme selectivity was shown to be mainly based on the position of the double bond closest to the carboxylic group. From the point of view of kinetics, purity and yield, YLL2 was the most effective lipase for DHA purification. Using this enzyme in an open reactor process resulted in the highest concentrations of DHA ethyl ester (77%) and ω-3 esters (81%) with a recovery of 94% and 77% respectively.