Quantitative study of lipase secretion, extracellular lipolysis, and lipid storage in the yeast Yarrowia lipolytica grown in the presence of olive oil: analogies with lipolysis in humans

Exploring the use of hexadecane by Yarrowia lipolytica: Effect of dissolved oxygen and medium supplementation

This work aimed to evaluate the effect of medium composition and volumetric oxygen transfer coefficient (kLa) on Y. lipolytica growth and production of microbial lipids and enzymes from hexadecane. In the stirred tank bioreactor, increasing kLa from 11 h-1 to 132 h-1 improved the hexadecane assimilation rate, biomass concentration, and lipids synthesis (0.90 g·L-1). A cost-effective hexadecane-based medium supplemented with corn steep liquor and a low amount of ammonium sulfate boosted lipids production up to 2.1 g·L-1, composed of palmitic, palmitoleic, oleic, and linoleic acids. The unsaturated/saturated fraction was dependent on the C/N ratio. Lipids of Y. lipolytica CBS 2075 are promising feedstock for animal feed, food additives, or the biodiesel industry. Simultaneous synthesis of extracellular lipase and protease from hexadecane was observed, which is a new feature that was not previously reported. The highest enzyme activity was obtained at the highest C/N ratio conditions. These results open new perspectives on the application of Y. lipolytica-based cultures for the biotransformation of hexadecane-polluted streams into valuable compounds, fulfilling an interesting strategy towards the circular economy concept.

Extracellular lipase production by Yarrowia lipolytica under magnetic fields

This study aimed at estimating cultivation conditions to enable Yarrowia lipolytica NNRL Y-1095 to produce extracellular lipase and at evaluating the influence of magnetic fields (MF) on the lipase production and on its catalytic conditions. Culture conditions of carbon sources and surfactant defined to produce extracellular lipase were 10 g L-1 glucose, 15 g L-1 olive oil and 2 g L-1 Triton X-100. The highest lipase activity (34.8 U mL-1) was reached after 144 h when MFs were applied from 72 to 144 h of culture. It corresponds to an increase of 287.5% by comparison with the highest lipase activity in the control culture. MF application from 72 to 144 h did not change the optimal temperature of lipase, which was 37 °C, by comparison with the control. However, the optimal pH of the control was 7.0 while the one of lipase produced with MF was 8.0. Findings highlighted that the presence of MFs led to increase in synthesis of lipase by Y. lipolytica, with changes in the catalytic profile. This is one of the first studies of MF application to Y. lipolytica NRRL Y-1095 cultures to produce lipase.

Enhancing Red Yeast Biomass Yield and Lipid Biosynthesis by Using Waste Nitrogen Source by Glucose Fed-Batch at Low Temperature

This work reports the effect of simple feeding strategies and temperature to obtain high-cell-density cultures of Rhodotorula glutinis var. rubescens LOCKR13 maximizing the de novo lipid productivity using deproteinated potato wastewater (DPW) as a basic medium. Feeding DPW with glucose enables a high yield of Rhodotorula glutinis var. rubescens LOCKR13 biomass (52 g d.w. L−1) to be obtained. The highest values of lipid accumulation (34.15%, w/w), production (14.68 g L−1) and yield coefficients (YL/S: 0.242 g g−1), and volumetric productivity (PL: 0.1 g L−1 h−1) were reached by the strain in the two-stage fed-batch process at 20 °C. The lipid of yeast biomass was rich in oleic acid (Δ9C18:1) and palmitic acid (C16:0), and the lower temperature of incubation significantly increased the MUFA (especially oleic acid) content. For the first time, a unique set of thermal analyses of the microbial oil was performed. The isotherms of the oxidation kinetics (PDSC) showed that lipids extracted from the biomass of red yeast had high oxidative stability. This feature of the yeast oil can be useful for long-shelf-life food products and can be promising for the production of biodiesel.

Attempt to Develop an Effective Method for the Separation of Gamma-Decalactone from Biotransformation Medium

Gamma-decalactone (GDL) is a fragrance compound obtained in the process of β-oxidation of ricinoleic acid, which is derived from the hydrolysis of castor oil. The biotechnological method of the synthesis of this lactone has been improved for over two decades, but the vast majority of research results have been based only on determining the concentration of the lactone by chromatographic methods without separating it from the biotransformation medium. In this study, we attempted to separate GDL from the medium in which the lactone was synthesized by Yarrowia lipolytica from castor oil. The effectiveness of liquid–liquid extraction, hydrodistillation, and adsorption on the porous materials (zeolite, vermiculite and resin Amberlite XAD-4) was compared. The influence of the solvent on the efficiency of GDL extraction, the influence of the acidity of the medium on the amount of GDL in the distillate, and the level of lactone adsorption on the above-mentioned adsorbents were compared by calculating the initial adsorption rate. The adsorption isotherm was determined for the most effective adsorbent. Among the five solvents tested, the most effective was diethyl ether, used at the ratio of 1:1. The extraction was characterized by higher efficiency than hydrodistillation; the difference in GDL determinations by these two methods ranged from 12.8 to 22%. The purity of the distillates was much higher than that of the extracts at 88.0 ± 3.4% compared to 53.0 ± 1.8%. The acidification of the biotransformation medium increased the concentration of the lactone in both the reaction mixture and the distillate. GDL was most efficiently adsorbed on Amberlite XAD-4 resin, for which the lactone isotherm adsorption was linear. The amount of lactone adsorbed on Amberlite XAD-4 within 1 h was approx. 80% (2.45 g), of which 1.96 g was then desorbed with ethanol. In the context of industrial applications, adsorption of GDL on Amberlite XAD-4 seems to be the most appropriate method due to material costs, the ease of the process, and low environmental burden.

Cleaner degreasing of sheepskins by the Yarrowia lipolytica LIP2 lipase as a chemical-free alternative in the leather industry

Conventional degreasing of skins and hides in the leather industry requires high amounts of organic solvents and detergents that cause environmental issues. In this study, the LIP2 lipase from the yeast Yarrowia lipolytica (YLLIP2) was shown to be effective in degreasing sheepskins, thus reducing the amount of harmful chemicals. Using 6 mg of lipase/kg of raw skin, successful degreasing was achieved in only 15 min at pH 8 and 30°C. ToF-SIMS mass spectra of chemically and enzymatically treated sheepskinsare consistent with a selective elimination process for the enzymatic treatment. Comparative SEM microscopy, ATR-FTIR spectroscopy and physicochemical analyses showed better properties of the enzymatically treated leather than those of the chemically treated leather. Effluent physicochemical parameters showed that the enzymatic treatment is a cleaner degreasing operation. Altogether, this work opens new horizons to use the YLLIP2 lipase as a more efficient alternative in the leather industry.

Optimizing the catalytic activities of methanol and thermotolerant Kocuria flava lipases for biodiesel production from cooking oil wastes

In this study, two highly thermotolerant and methanol-tolerant lipase-producing bacteria were isolated from cooking oil and they exhibited a high number of catalytic lipase activities recording 18.65 ± 0.68 U/mL and 13.14 ± 0.03 U/mL, respectively. Bacterial isolates were identified according to phenotypic and genotypic 16S rRNA characterization as Kocuria flava ASU5 (MT919305) and Bacillus circulans ASU11 (MT919306). Lipases produced from Kocuria flava ASU5 showed the highest methanol tolerance, recording 98.4% relative activity as well as exhibited high thermostability and alkaline stability. Under the optimum conditions obtained from 3D plots of response surface methodology design, the Kocuria flava ASU5 biocatalyst exhibited an 83.08% yield of biodiesel at optimized reaction variables of, 60 ○C, pH value 8 and 1:2 oil/alcohol molar ratios in the reaction mixture. As well as, the obtained results showed the interactions of temperature/methanol were significant effects, whereas this was not noted in the case of temperature/pH and pH/methanol interactions. The obtained amount of biodiesel from cooking oil was 83.08%, which was analyzed by a GC/Ms profile. The produced biodiesel was confirmed by Fourier-transform infrared spectroscopy (FTIR) approaches showing an absorption band at 1743 cm-1, which is recognized for its absorption in the carbonyl group (C=O) which is characteristic of ester absorption. The energy content generated from biodiesel synthesized was estimated as 12,628.5 kJ/mol. Consequently, Kocuria flava MT919305 may provide promising thermostable, methanol-tolerant lipases, which may improve the economic feasibility and biotechnology of enzyme biocatalysis in the synthesis of value-added green chemicals.

Transcriptome Analysis of Oleaginous Fungus Mucor circinelloides WJ11 in Response to Exogenous Soybean Oil as Carbon Source

Mucor circinelloides is an oleaginous fungus that utilizes a wide variety of carbon substrates for its growth. The different sources of carbon strongly influence the total lipid content of the fungus. These different carbon substrates are assimilated and dissimilated through different metabolic pathways before entering into the TAG synthesis pathway. In the present study, we attempted to explore the mechanism of ex-novo lipid biosynthesis in M. circinelloides WJ11 in response to exogenous plant oil as a carbon source through transcriptomic analysis. The lipid content of WJ11 grown in a media containing mixed soybean oil with glucose as a carbon source was up to 43.8%, an increase of 13.9% as compared to glucose alone as the carbon source. RNA-Seq analysis was performed to investigate global gene expression patterns in the oil-treated WJ11. Based on RNA-seq analysis, among the 4646 differentially expressed genes (DEGs), 2379 were up-regulated and 2267 down-regulated. The expression of acetyl-CoA synthetase, 6-phosphofructokinase, alcohol dehydrogenase (NADP+), fructose-bisphosphate aldolase, and pyruvate kinase was down-regulated while genes related to triglyceride synthesis were up-regulated. The majority of genes and pathways related to lipid biosynthesis were up-regulated indicating a diversion of metabolic pathways towards lipid biosynthesis. The data generated advance the genomic resources and provide insights into the mechanisms of ex-novo lipid accumulation in fungi that use exogenous oil as a carbon source.

Aeration and Stirring in Yarrowia lipolytica Lipase Biosynthesis during Batch Cultures with Waste Fish Oil as a Carbon Source

Yarrowia lipolytica is one of the most studied non-conventional forms of yeast, exhibiting a high secretory capacity and producing many industrially important and valuable metabolites. The yeast conceals a great biotechnological potential to synthesize organic acids, sweeteners, microbial oil, or fragrances. The vast majority of bioprocesses are carried out in bioreactors, where suitable culture conditions are provided. In the current study, the effect of agitation speed (200–600 rpm) and air flow rate (0.0375–2.0 dm3/(dm3 × min)) on the biomass yield and lipase activity of Y. lipolytica KKP 379 is analyzed in a growth medium containing waste fish oil. The increase of aeration intensity limited the period of oxygen deficit in the medium. Simultaneously, an increase in lipolytic activity was observed from 2.09 U/cm3 to 14.21 U/cm3; however, an excessive agitation speed likely caused oxidative or shear stresses, and a reduction in lipolytic activity was observed. Moreover, it is confirmed that the synthesis of lipases is related to oxygen consumption, pH, and the yeast growth phase, and appropriate process selection may provide two advantages, namely, the maximum use of the waste carbon source and the production of lipolytic enzymes that are valuable in many industries.

Animal Fat as a Substrate for Production of n-6 Fatty Acids by Fungal Solid-State Fermentation

The method of solid-state fermentation (SSF) represents a powerful technology for the fortification of animal-based by-products. Oleaginous Zygomycetes fungi are efficient microbial cell factories used in SSF to valorize a wide range of waste and rest cereal materials. The application of this fermentation technique for utilization and biotransformation of animal-based materials represents a distinguished step in their treatment. In this study, for the first time, the strain Umbelopsis isabellina CCF2412 was used for the bioconversion of animal fat by-products to the fermented bioproducts enriched with n-6 polyunsaturated fatty acids, mainly γ-linolenic acid (GLA). Bioconversion of both cereals and the animal fat by-product resulted in the production of fermented bioproducts enriched with not just GLA (maximal yield was 6.4 mg GLA/g of fermented bioproduct), but also with high yields of glucosamine. Moreover, the fermentation on the cornmeal matrix led to obtaining bioproduct enriched with β-carotene. An increased amount of β-carotene content improved the antioxidant stability of obtained fermented bioproducts. Furthermore, the application of Fourier-transform infrared spectroscopy for rapid analysis and characterization of the biochemical profile of obtained SSF bioproducts was also studied.

The digestion of galactolipids and its ubiquitous function in Nature for the uptake of the essential α-linolenic acid

Galactolipids, mainly monogalactosyl diglycerides and digalactosyl diglycerides are the main lipids found in the membranes of plants, algae and photosynthetic microorganisms like microalgae and cyanobacteria. As such, they are the main lipids present at the surface of earth. They may represent up to 80% of the fatty acid stocks, including a large proportion of polyunsaturated fatty acids mainly α-linolenic acid (ALA). Nevertheless, the interest in these lipids for nutrition and other applications remains overlooked, probably because they are dispersed in the biomass and are not as easy to extract as vegetable oils from oleaginous fruit and oil seeds. Another reason is that galactolipids only represent a small fraction of the acylglycerolipids present in modern human diet. In herbivores such as horses, fish and folivorous insects, galactolipids may however represent the main source of dietary fatty acids due to their dietary habits and digestion physiology. The development of galactolipase assays has led to the identification and characterization of the enzymes involved in the digestion of galactolipids in the gastrointestinal tract, as well as by microorganisms. Pancreatic lipase-related protein 2 (PLRP2) has been identified as an important factor of galactolipid digestion in humans, together with pancreatic carboxyl ester hydrolase (CEH). The levels of PLRP2 are particularly high in monogastric herbivores thus highlighting the peculiar role of PLRP2 in the digestion of plant lipids. Similarly, pancreatic lipase homologs are found to be expressed in the midgut of folivorous insects, in which a high galactolipase activity can be measured. In fish, however, CEH is the main galactolipase involved. This review discusses the origins and fatty acid composition of galactolipids and the physiological contribution of galactolipid digestion in various species. This overlooked aspect of lipid digestion ensures not only the intake of ALA from its main natural source, but also the main lipid source of energy for growth of some herbivorous species.

Grease Waste as a Reservoir of Lipase-Producing Yeast and Description of Limtongella siamensis gen. nov., sp. nov

A total of 175 yeast isolates were obtained from grease samples. Based on the D1/D2 region of the large subunit (LSU) ribosomal RNA (rRNA) gene analysis, 150 yeast isolates were identified as belonging to 36 described yeast species, whereas 25 isolates required more analysis. Among the described species, Rhodotorula mucilaginosa was the only Basidiomycetous yeast, whereas 149 isolates were identified as belonging to 35 described species of 15 genera in the phylum Ascomycota, and Candida tropicalis was the most abundant species. A study of lipase production indicated that strain DMKU-JMGT1-45 showed volumetric activity of 38.89 ± 9.62 and 155.56 ± 14.70 U/mL when grown in yeast extract malt extract (YM) and YM supplemented with 1% olive oil, respectively. In addition, this strain intracellularly accumulated lipid, of which the fatty acid profile revealed the major fatty acids to be 39.9% oleic acid (C18:1), 27.61% palmitoleic acid (C16:1) and 14.97% palmitic acid (C16:0). A phylogenetic analysis of the combined multi-locus gene sequences showed that the strains DMKU-JMGT1-45^T and DMKU-JMGT4-14 formed a well-separated lineage and could not be assigned to any of the currently recognized genera of the Saccharomycetales. Limtongella siamensis gen. nov., sp. nov. is therefore proposed to accommodate these two strains as members of the order Saccharomycetales.

An Insight into Storage Lipid Synthesis by Yarrowia lipolytica Yeast Relating to Lipid and Sugar Substrates Metabolism

Single cell oil (SCO) is the lipid accumulated in the cells of oleaginous microorganisms. Cellular lipids can be synthesized in two different pathways: de novo by metabolizing hydrophilic substrates and ex novo by fermenting hydrophobic substrates. The aim of the study was to evaluate the effect of carbon source (glucose and olive oil) in the culture medium on the course of microbial oil accumulation in Y.lipolytica cells. The level of selected gene expression by real time quantitative PCR method was investigated. The significant increase in expression of the POX2 gene encoding acyl-CoA oxidase II, which preferentially oxidizes long-chain acyl-CoAs formed from substrate fatty acids incorporated inside the microbial cell, was observed in medium with olive oil in relation to glucose containing medium. Noteworthily, the presence of lipid carbon substrate did not inhibit the level of ACL gene transcription coding for ATP-citrate lyase, the key enzyme of the lipid de novo accumulation process. The present study indicated that de novo lipid biosynthesis could occur despite the presence of fatty acids in the medium, and the synthesis of storage lipids in the presence of lipid carbon substrates could be carried out with the use of both pathways (de novo and ex novo).

Vegetable oils as carbon and energy source for Aureobasidium melanogenum in batch cultivation

Dark homogenous fungal‐based layers called biofinishes and vegetable oils are key ingredients of an innovative wood protecting system. The aim of this study was to determine which of the vegetable oils that have been used to generate biofinishes on wood will provide carbon and energy for the biofinish‐inhabiting fungus Aureobasidium melanogenum, and to determine the effect of the oil type and the amount of oil on the cell yield. Aureobasidium melanogenum was cultivated in shake flasks with different types and amounts of carbon‐based nutrients. Oil‐related total cell and colony‐forming unit growth were demonstrated in suspensions with initially 1% raw linseed, stand linseed, and olive oil. Oil‐related cell growth was also demonstrated with raw linseed oil, using an initial amount of 0.02% and an oil addition during cultivation. Nile red staining showed the accumulation of fatty acids inside cells grown in the presence of oil. In conclusion, each tested vegetable oil was used as carbon and energy source by A. melanogenum. The results indicated that stand linseed oil provides less carbon and energy than olive and raw linseed oil. This research is a fundamental step in unraveling the effects of vegetable oils on biofinish formation.

Galactolipase activity of Talaromyces thermophilus lipase on galactolipid micelles, monomolecular films and UV-absorbing surface-coated substrate

Talaromyces thermophilus lipase (TTL) was found to hydrolyze monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG) substrates presented in various forms to the enzyme. Different assay techniques were used for each substrate: pHstat with dioctanoyl galactolipid-bile salt mixed micelles, barostat with dilauroyl galactolipid monomolecular films spread at the air-water interface, and UV absorption using a novel MGDG substrate containing α-eleostearic acid as chromophore and coated on microtiter plates. The kinetic properties of TTL were compared to those of the homologous lipase from Thermomyces lanuginosus (TLL), guinea pig pancreatic lipase-related protein 2 and Fusarium solani cutinase. TTL was found to be the most active galactolipase, with a higher activity on micelles than on monomolecular films or surface-coated MGDG. Nevertheless, the UV absorption assay with coated MGDG was highly sensitive and allowed measuring significant activities with about 10 ng of enzymes, against 100 ng to 10 μg with the pHstat. TTL showed longer lag times than TLL for reaching steady state kinetics of hydrolysis with monomolecular films or surface-coated MGDG. These findings and 3D-modelling of TTL based on the known structure of TLL pointed out to two phenylalanine to leucine substitutions in TTL, that could be responsible for its slower adsorption at lipid-water interface. TTL was found to be more active on MGDG than on DGDG using both galactolipid-bile salt mixed micelles and galactolipid monomolecular films. These later experiments suggest that the second galactose on galactolipid polar head impairs the enzyme adsorption on its aggregated substrate.

Fungal Screening on Olive Oil for Extracellular Triacylglycerol Lipases: Selection of a Trichoderma harzianum Strain and Genome Wide Search for the Genes

A lipolytic screening with fungal strains isolated from lignocellulosic waste collected in banana plantation dumps was carried out. A Trichoderma harzianum strain (B13-1) showed good extracellular lipolytic activity (205 UmL⁻¹). Subsequently, functional screening of the lipolytic activity on Rhodamine B enriched with olive oil as the only carbon source was performed. The successful growth of the strain allows us to suggest that a true lipase is responsible for the lipolytic activity in the B13-1 strain. In order to identify the gene(s) encoding the protein responsible for the lipolytic activity, in silico identification and characterization of triacylglycerol lipases from T. harzianum is reported for the first time. A survey in the genome of this fungus retrieved 50 lipases; however, bioinformatic analyses and putative functional descriptions in different databases allowed us to choose seven lipases as candidates. Suitability of the bioinformatic screening to select the candidates was confirmed by reverse transcription polymerase chain reaction (RT-PCR). The gene codifying 526309 was expressed when the fungus grew in a medium with olive oil as carbon source. This protein shares homology with commercial lipases, making it a candidate for further applications. The success in identifying a lipase gene inducible with olive oil and the suitability of the functional screening and bioinformatic survey carried out herein, support the premise that the strategy can be used in other microorganisms with sequenced genomes to search for true lipases, or other enzymes belonging to large protein families.

Bioinformatical analysis and preliminary study of the role of lipase in lipid metabolism in Mucor circinelloides

The filamentous fungusMucor circinelloideshas been widely used as a model organism to investigate the mechanisms of lipid accumulation.

Monitoring lipase/esterase activity by stopped flow in a sequential injection analysis system using p-nitrophenyl butyrate

Lipases and esterases are biocatalysts used at the laboratory and industrial level. To obtain the maximum yield in a bioprocess, it is important to measure key variables, such as enzymatic activity. The conventional method for monitoring hydrolytic activity is to take out a sample from the bioreactor to be analyzed off-line at the laboratory. The disadvantage of this approach is the long time required to recover the information from the process, hindering the possibility to develop control systems. New strategies to monitor lipase/esterase activity are necessary. In this context and in the first approach, we proposed a lab-made sequential injection analysis system to analyze off-line samples from shake flasks. Lipase/esterase activity was determined using p-nitrophenyl butyrate as the substrate. The sequential injection analysis allowed us to measure the hydrolytic activity from a sample without dilution in a linear range from 0.05-1.60 U/mL, with the capability to reach sample dilutions up to 1000 times, a sampling frequency of five samples/h, with a kinetic reaction of 5 min and a relative standard deviation of 8.75%. The results are promising to monitor lipase/esterase activity in real time, in which optimization and control strategies can be designed.

Yarrowia lipolytica and its multiple applications in the biotechnological industry

Yarrowia lipolytica is a nonpathogenic dimorphic aerobic yeast that stands out due to its ability to grow in hydrophobic environments. This property allowed this yeast to develop an ability to metabolize triglycerides and fatty acids as carbon sources. This feature enables using this species in the bioremediation of environments contaminated with oil spill. In addition, Y. lipolytica has been calling the interest of researchers due to its huge biotechnological potential, associated with the production of several types of metabolites, such as bio-surfactants, γ-decalactone, citric acid, and intracellular lipids and lipase. The production of a metabolite rather than another is influenced by the growing conditions to which Y. lipolytica is subjected. The choice of carbon and nitrogen sources to be used, as well as their concentrations in the growth medium, and the careful determination of fermentation parameters, pH, temperature, and agitation (oxygenation), are essential for efficient metabolites production. This review discusses the biotechnological potential of Y. lipolytica and the best growing conditions for production of some metabolites of biotechnological interest.

Characterization of the two intracellular lipases of Y. lipolytica encoded by TGL3 and TGL4 genes: new insights into the role of intracellular lipases and lipid body organisation

Eukaryotes store lipids in a specialised organelle, the lipid body (LB), mainly as triglycerides (TAGs). Both the rates of synthesis and degradation contribute to the control of the accumulation of TAGs. The synthesis of TAGs in yeasts has been well documented, especially in the model yeast Saccharomyces cerevisiae and in the oleaginous yeast Yarrowia lipolytica. However, descriptions of the processes involved in TAG degradation are more scarce and mostly for S. cerevisiae. Here, we report the characterisation of two Y. lipolytica genes, YlTGL3 and YlTGL4, encoding intracellular lipases involved in TAG degradation. The two proteins are localised in lipid bodies, and YlTgl4 was mainly found at the interface between LBs. Surprisingly, the spatial organisation of YlTgl3 and YlTgl4 depends on the culture medium and on the physiological phase of the cell. Inactivation of one or both genes doubles the lipid accumulation capacity of Y. lipolytica, increasing the cell's capacity to accumulate TAGs. The amino acid sequence of YlTgl4 contains the consensus sequence motif (G/A)XSXG, typical of serine hydrolases, whereas YlTgl3 does not. Single and double mutants are unable to degrade TAGs, and higher expression of YlTgl4 correlates with TAG degradation. Therefore, we propose that YlTgl4 is the main lipase responsible for TAG degradation and that YlTgl3 may act as a positive regulator of YlTgl4 rather than a functional lipase. Thus, contrary to S. cerevisiae, Y. lipolytica possesses two intracellular lipases with distinct roles and with distinct localisations in the LB.

New tools for exploring "old friends-microbial lipases"

Fat-splitting enzymes (lipases), due to their natural, industrial, and medical relevance, attract enough attention as fats do in our lives. Starting from the paper that we write, cheese and oil that we consume, detergent that we use to remove oil stains, biodiesel that we use as transportation fuel, to the enantiopure drugs that we use in therapeutics, all these applications are facilitated directly or indirectly by lipases. Due to their uniqueness, versatility, and dexterity, decades of research work have been carried out on microbial lipases. The hunt for novel lipases and strategies to improve them continues unabated as evidenced by new families of microbial lipases that are still being discovered mostly by metagenomic approaches. A separate database for true lipases termed LIPABASE has been created recently which provides taxonomic, structural, biochemical information about true lipases from various species. The present review attempts to summarize new approaches that are employed in various aspects of microbial lipase research, viz., screening, isolation, production, purification, improvement by protein engineering, and surface display. Finally, novel applications facilitated by microbial lipases are also presented.

Expression of a lipid-inducible, self-regulating form of Yarrowia lipolytica lipase LIP2 in Saccharomyces cerevisiae

Saccharomyces cerevisiae is frequently used as a bioreactor for conversion of exogenously acquired metabolites into value-added products, but has not been utilized for bioconversion of low-cost lipids such as triacylglycerols (TAGs) because the cells are typically unable to acquire these lipid substrates from the growth media. To help circumvent this limitation, the Yarrowia lipolytica lipase 2 (LIP2) gene was cloned into S. cerevisiae expression vectors and used to generate S. cerevisiae strains that secrete active Lip2 lipase (Lip2p) enzyme into the growth media. Specifically, LIP2 expression was driven by the S. cerevisiae PEX11 promoter, which maintains basal transgene expression levels in the presence of sugars in the culture medium but is rapidly upregulated by fatty acids. Northern blotting, lipase enzyme activity assays, and gas chromatographic measurements of cellular fatty acid composition after lipid feeding all confirmed that cells transformed with the PEX11 promoter-LIP2 construct were responsive to lipids in the media, i.e., cells expressing LIP2 responded rapidly to either free fatty acids or TAGs and accumulated high levels of the corresponding fatty acids in intracellular lipids. These data provided evidence of the creation of a self-regulating positive control feedback loop that allows the cells to upregulate Lip2p production only when lipids are present in the media. Regulated, autonomous production of extracellular lipase activity is a necessary step towards the generation of yeast strains that can serve as biocatalysts for conversion of low-value lipids to value-added TAGs and other novel lipid products.