Novel microbial lipases: catalytic activity in reactions in organic media

Agri-residues and agro-industrial waste substrates bioconversion by fungal cultures to biocatalyst lipase for green chemistry: A review

Huge amounts of agri-residues generated from food crops and processing are discarded in landfills, causing environmental problems. There is an urgent need to manage them with a green technological approach. Agri-residues are rich in nutrients such as proteins, lipids, sugars, minerals etc., and provide an opportunity for bioconversion into value-added products. Considering the importance of lipase as a biocatalyst for various industrial applications and its growing need for economic production, a detailed review of bioconversion of agri-residues and agro-industrial substrate for the production of lipase from fungal species from a technological perspective has been reported for the first time. Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flow diagram was used for the identification and selection of articles from ScienceDirect, Google Scholar, and Scopus databases from 2010 to 2023 (July), and 108 peer-reviewed journal articles were included based on the scope of the study. The composition of agri-residues/agro-industrial wastes, fungal species, lipase production, industrial/green chemistry applications, and the economic impact of using agri-residues on lipase costs have been discussed. Bioconversion procedure, process developments, and technology gaps required to be addressed before commercialization have also been discussed. This process expects to decrease the environmental pollution from wastes, and low-cost lipase can help in the growth of the bioeconomy.

Enhanced Activity and Stability of an Acetyl Xylan Esterase in Hydrophilic Alcohols through Site-Directed Mutagenesis

Current demands for the development of suitable biocatalysts showing high process performance is stimulated by the need to replace current chemical synthesis with cleaner alternatives. A drawback to the use of biocatalysts for unique applications is their low performance in industrial conditions. Hence, enzymes with improved performance are needed to achieve innovative and sustainable biocatalysis. In this study, we report the improved performance of an engineered acetyl xylan esterase (BaAXE) in a hydrophilic organic solvent. The structure of BaAXE was partitioned into a substrate-binding region and a solvent-affecting region. Using a rational design approach, charged residues were introduced at protein surfaces in the solvent-affecting region. Two sites present in the solvent-affecting region, A12D and Q143E, were selected for site-directed mutagenesis, which generated the mutants MUT12, MUT143 and MUT12-143. The mutants MUT12 and MUT143 reported lower Km (0.29 mM and 0.27 mM, respectively) compared to the wildtype (0.41 mM). The performance of the mutants in organic solvents was assessed after enzyme incubation in various strengths of alcohols. The mutants showed improved activity and stability compared to the wild type in low strengths of ethanol and methanol. However, the activity of MUT143 was lost in 40% methanol while MUT12 and MUT12-143 retained over 70% residual activity in this environment. Computational analysis links the improved performance of MUT12 and MUT12-143 to novel intermolecular interactions that are absent in MUT143. This work supports the rationale for protein engineering to augment the characteristics of wild-type proteins and provides more insight into the role of charged residues in conferring stability.

Serratia sp. scl1: isolation of a novel thermostable lipase producing microorganism which holds industrial importance

Lipase being a hydrolysable enzyme plays a major role in serving various purposes of the industries. Thus, it is very important to have a sustainable and efficient source of this enzyme. In this present study, several microorganisms were isolated from medicinal effluent of a pharmaceutical industry that could produce efficient lipase activity. Among these isolates, a designated strain scl1 was isolated and based on the molecular and biochemical characterisation was tentatively assigned to the genus Serratia. Preliminary studies confirmed the strain scl1 was found to exhibit the highest production of lipase at a temperature and pH of 35 °C and 7, respectively under the incubation for 48 h. Further, the lipase activity was measured by following spectrophotometric method using pNPP as the substrate in which the Km and Vmax of the crude enzyme was found to be 3.349 × 10^-3 M and 5.68 × 10^-1 unit/mL, respectively. The extracellular crude lipase was found to show a temperature and pH optima of 75 °C and 8, respectively which gave a strong indication that the enzyme appeared to be highly thermostable. This study revealed the strain scl1 is able to produce a thermostable lipase which can meet the needs of the modern-day industrialization techniques. However, more work is required to purify the enzyme and get it ready for commercial applications.

Microbial lipases and their industrial applications: a comprehensive review

Lipases are very versatile enzymes, and produced the attention of the several industrial processes. Lipase can be achieved from several sources, animal, vegetable, and microbiological. The uses of microbial lipase market is estimated to be USD 425.0 Million in 2018 and it is projected to reach USD 590.2 Million by 2023, growing at a CAGR of 6.8% from 2018. Microbial lipases (EC 3.1.1.3) catalyze the hydrolysis of long chain triglycerides. The microbial origins of lipase enzymes are logically dynamic and proficient also have an extensive range of industrial uses with the manufacturing of altered molecules. The unique lipase (triacylglycerol acyl hydrolase) enzymes catalyzed the hydrolysis, esterification and alcoholysis reactions. Immobilization has made the use of microbial lipases accomplish its best performance and hence suitable for several reactions and need to enhance aroma to the immobilization processes. Immobilized enzymes depend on the immobilization technique and the carrier type. The choice of the carrier concerns usually the biocompatibility, chemical and thermal stability, and insolubility under reaction conditions, capability of easy rejuvenation and reusability, as well as cost proficiency. Bacillus spp., Achromobacter spp., Alcaligenes spp., Arthrobacter spp., Pseudomonos spp., of bacteria and Penicillium spp., Fusarium spp., Aspergillus spp., of fungi are screened large scale for lipase production. Lipases as multipurpose biological catalyst has given a favorable vision in meeting the needs for several industries such as biodiesel, foods and drinks, leather, textile, detergents, pharmaceuticals and medicals. This review represents a discussion on microbial sources of lipases, immobilization methods increased productivity at market profitability and reduce logistical liability on the environment and user.

Main Structural Targets for Engineering Lipase Substrate Specificity

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

Covalent Immobilization of Candida rugosa Lipase on Epichlorohydrin-Coated Magnetite Nanoparticles: Enantioselective Hydrolysis Studies of Some Racemic Esters and HPLC Analysis

In this study, a new biocatalyst was prepared by immobilizing Candida rugosa lipase epichlorohydrin-functionalized onto the surface of the nanoparticles. Magnetite nanoparticles were obtained by chemical co-precipitation method of Fe²⁺ and Fe³⁺, and then the prepared uncoated and coated nanoparticles were characterized by XRD, FT-IR and TGA. Lipase was covalently attached to activated nanoparticles. The catalytic properties of free and immobilized lipases were determined. It was found that the optimum temperature for free and immobilized lipases was 30 °C and 35 °C, respectively. The optimum pH values were found to be 7.0 and 8 for free and immobilized lipases, respectively. Immobilized lipase was found to retain significant activity even after the seventh use. In the final section of the study, optically pure compounds were obtained by carrying out the enantioselective hydrolysis studies of racemic esters by using immobilized lipase. Enantiomeric excesses of the products in the enantioselective hydrolysis of racemic ibuprofen and naproxen methyl ester and racemic butyl mandelate were determined to be 94.93, 77.30 and 68.15, respectively.

Design and Construction of Hybrid Microcapsules with Higher-Order Structure and Multiple Functions

The construction of inorganic-protein hybrid microcapsules by using bovine serum albumin, metal ion clusters, and poly (N-isopropylacrylamide) nanoconjugates as building blocks is presented. These microcapsules have robust membranes, which can keep their spherical morphology. They support interfacial catalytic activity by the ion clusters on their surface, and can be used as a platform to immobilize enzyme on the interface of oil/water to increase the diversity and efficiency of catalysis. These microcapsules also act as a container to make materials away from bacteria when existing silver clusters on the membrane. The obtained results highlight the construction of these microcompartments. These novel microcompartments can provide some new opportunities in bottom-up synthetic biology, bioinspired microstorage/ microreactor, and drug/gene delivery in the future.

Environmental Factors Modulating the Stability and Enzymatic Activity of the Petrotoga mobilis Esterase (PmEst)

Enzymes isolated from thermophilic organisms found in oil reservoirs can find applications in many fields, including the oleochemical, pharmaceutical, bioenergy, and food/dairy industries. In this study, in silico identification and recombinant production of an esterase from the extremophile bacteria Petrotoga mobilis (designated PmEst) were performed. Then biochemical, bioinformatics and structural characterizations were undertaken using a combination of synchrotron radiation circular dichroism (SRCD) and fluorescence spectroscopies to correlate PmEst stability and hydrolytic activity on different substrates. The enzyme presented a high Michaelis-Menten constant (KM 0.16 mM) and optimum activity at ~55°C for p-nitrophenyl butyrate. The secondary structure of PmEst was preserved at acid pH, but not under alkaline conditions. PmEst was unfolded at high concentrations of urea or guanidine through apparently different mechanisms. The esterase activity of PmEst was preserved in the presence of ethanol or propanol and its melting temperature increased ~8°C in the presence of these organic solvents. PmEst is a mesophilic esterase with substrate preference towards short-to medium-length acyl chains. The SRCD data of PmEst is in agreement with the prediction of an α/β protein, which leads us to assume that it displays a typical fold of esterases from this family. The increased enzyme stability in organic solvents may enable novel applications for its use in synthetic biology. Taken together, our results demonstrate features of the PmEst enzyme that indicate it may be suitable for applications in industrial processes, particularly, when the use of polar organic solvents is required.

Eighteen new oleaginous yeast species

Of 1600 known species of yeasts, about 70 are known to be oleaginous, defined as being able to accumulate over 20 % intracellular lipids. These yeasts have value for fundamental and applied research. A survey of yeasts from the Phaff Yeast Culture Collection, University of California Davis was performed to identify additional oleaginous species within the Basidiomycota phylum. Fifty-nine strains belonging to 34 species were grown in lipid inducing media, and total cell mass, lipid yield and triacylglycerol profiles were determined. Thirty-two species accumulated at least 20 % lipid and 25 species accumulated over 40 % lipid by dry weight. Eighteen of these species were not previously reported to be oleaginous. Triacylglycerol profiles were suitable for biodiesel production. These results greatly expand the number of known oleaginous yeast species, and reveal the wealth of natural diversity of triacylglycerol profiles within wild-type oleaginous Basidiomycetes.

Inoculation of bacteria for the bioremediation of heavy metals contaminated soil by Agrocybe aegerita

The combination of mushrooms and bacteria was used as a novel technique to remediate soils polluted by heavy metals.

Comprehensive Analysis of a Yeast Lipase Family in the Yarrowia Clade

Lipases are currently the subject of intensive studies due to their large range of industrial applications. The Lip2p lipase from the yeast Yarrowia lipolytica (YlLIP2) was recently shown to be a good candidate for different biotechnological applications. Using a combination of comparative genomics approaches based on sequence similarity, synteny conservation, and phylogeny, we constructed the evolutionary scenario of the lipase family for six species of the Yarrowia clade. RNA-seq based transcriptome analysis revealed the primary role of LIP2 homologues in the assimilation of different substrates. Once identified, these YlLIP2 homologues were expressed in Y. lipolytica. The lipase Lip2a from Candida phangngensis was shown to naturally present better activity and enantioselectivity than YlLip2. Enantioselectivity was further improved by site-directed mutagenesis targeted to the substrate binding site. The mono-substituted variant V232S displayed enantioselectivity greater than 200 and a 2.5 fold increase in velocity. A double-substituted variant 97A-V232F presented reversed enantioselectivity, with a total preference for the R-enantiomer.

An organic solvent-stable lipase from a newly isolated Staphylococcus aureus ALA1 strain with potential for use as an industrial biocatalyst

In this study, a new strain, ALA1, was identified as Staphylococcus aureus by biochemical tests, and its 16S ribosomal DNA sequence was isolated from dromedary milk. ALA1 lipase production was optimized in shake flask experiments and measured with varying pH (3-11), temperature (20-55 °C) and substrate concentrations. The maximum lipase production was recorded at pH 8 and 30 °C for up to 30 H of culture period for the S. aureus ALA1 strain. Among the substrates tested, selected carbon sources, xylose, nitrogen source, yeast extract, and olive oil (1%) were suitable for maximizing lipase production. The effects of surfactants were investigated and showed that Tween 20, Tween 80, and Triton X-100 prevented lipase production. Interestingly, isolate ALA1 was able to grow in high concentrations of benzene or toluene (up to 50% (v/v)). Moreover, the lipolytic activity of the S. aureus ALA1 lipase was stimulated by diethyl ether, whereas almost 100% of S. aureus ALA1 lipase activity was retained in 25% acetone, acetonitrile, benzene, 2-propanol, ethanol, methanol, or toluene. Because of its stability in organic solvent, the S. aureus ALA1 lipase was used as a biocatalyst to synthesize high levels of added value molecules. S. aureus ALA1 lipase could be considered as an ideal choice for applications in detergent formulations because of its high stability and compatibility with various surfactants, oxidizing agents, and commercial detergents.

Isolation and screening of lipolytic fungi from coastal waters of the southern caspian sea (north of iran)

Background:

Lipases (acylglycerol acylhydrolase, E. C. 3. 1. 1. 3) are widely distributed among microorganisms, animals and plants, catalyzing the hydrolysis of triglycerides to free fatty acids and glycerol. Their commercial application includes pharmaceutical, chemical, and paper industries.

Objectives:

This study aimed to isolate and screen lipolytic fungi from coastal waters of the southern Caspian Sea by Internal Transcribed Spacer-Polymerase Chain Reaction (ITS-PCR), and to optimize their lipolytic activity, pH and temperature. The ITS regions possess a high variation among taxonomically distinct fungal species and even within species.

Materials and Methods:

All fungal were tested to determine their lipolytic activity by the Tributyrin agar plate assay. After DNA extraction, lipase-producing fungi were identified via ITS-PCR of rDNA region with ITS1 and ITS4 primers.

Results:

Four fungal species were isolated from water samples of the Caspian Sea (north of Iran) between February and June 2011. The nucleotide sequences reported for three of these isolates have been assigned accession numbers from NCBI Gene Bank database. Among these species, Cladosporium langeronii showed maximum lipolytic activity (34 U/mL) and maximum clear zone formation (6 mm) on the Tributyrin agar plates. The optimum pH and temperature for activity were 8.0 and 35°C, respectively.

Conclusions:

The findings of this study indicated that these isolates were plant pathogenic fungi, which entered seawater from the environment, and were likely to have a suitable lipase activity on plant oils.

Enhancing extracellular lipolytic enzyme production in an arctic bacterium, Psychrobacter sp. ArcL13, by using statistical optimization and fed-batch fermentation

A strain isolated from seawater samples in the Chuckchi Sea and exhibiting extracellular lipolytic activity was identified using 16S rRNA gene sequence analysis as Psychrobacter sp. ArcL13. The lipolytic enzyme exhibited cold-active properties and high hydrolytic activity toward p-nitrophenyl caprylate (C8), p-nitrophenyl decanoate (C10), and sunflower oil. Statistical optimization of the medium components was performed to enhance the production of cold-active extracellular lipolytic activity. Glucose, yeast extract (YE), and NaCl were selected as the main efficient nutrient sources. Fed-batch fermentation using optimized medium with concentrated YE as the main feeding material showed a maximum lipolytic activity of 10.7 U/mL, which was a 21-fold increase in production over unoptimized flask culture conditions. The information obtained in the present study could prove applicable to the production of cold-active lipase on a large scale.

The combination of functional metagenomics and an oil-fed enrichment strategy revealed the phylogenetic diversity of lipolytic bacteria overlooked by the cultivation-based method

Metagenomic screening and conventional cultivation have been used to exploit microbial lipolytic enzymes in nature. We used an indigenous forest soil (NS) and oil-fed enriched soil (OS) as microbial and genetic resources. Thirty-four strains (17 each) of lipolytic bacteria were isolated from the NS and OS microcosms. These isolates were classified into the (sub)phyla Betaproteobacteria, Gammaproteobacteria, Firmicutes, and Actinobacteria, all of which are known to be the main microbial resources of commercially available lipolytic enzymes. Seven and 39 lipolytic enzymes were successfully retrieved from the metagenomic libraries of the NS and OS microcosms, respectively. The screening efficiency (a ratio of positive lipolytic clones to the total number of environmental clones) was markedly higher in the OS microcosm than in the NS microcosm. Moreover, metagenomic clones encoding the lipolytic enzymes associated with Alphaproteobacteria, Deltaproteobacteria, Acidobacteria, Armatimonadetes, and Planctomycetes and hitherto-uncultivated microbes were recovered from these libraries. The results of the present study indicate that functional metagenomics can be effectively used to capture as yet undiscovered lipolytic enzymes that have eluded the cultivation-based method, and these combined approaches may be able to provide an overview of lipolytic organisms potentially present in nature.

Esterase Active in Polar Organic Solvents from the Yeast Pseudozyma sp. NII 08165

Esterases/lipases active in water miscible solvents are highly desired in biocatalysis where substrate solubility is limited and also when the solvent is desired as an acyl acceptor in transesterification reactions, as with the case of biodiesel production. We have isolated an esterase from the glycolipid producing yeast-Pseudozyma sp. NII 08165 which in its crude form was alkali active, thermo stable, halo tolerant and also capable of acting in presence of high methanol concentration. The crude enzyme which maintained 90% of its original activity after being treated at 70°C was purified and the properties were characterized. The partially purified esterase preparation had temperature and pH optima of 60°C and 8.0 respectively. The enzyme retained almost complete activity in presence of 25% methanol and 80% activity in the same strength of ethanol. Conditions of enzyme production were optimized, which lead to 9 fold increase in the esterase yield. One of the isoforms of the enzyme LIP1 was purified to homogeneity and characterized. Purified LIP1 had a K m and V max of 0.01 and 1.12, respectively. The purified esterase lost its thermo and halo tolerance but interestingly, retained 97% activity in methanol.

Metal ion activated lipase from halotolerant Bacillus sp. VITL8 displays broader operational range

Lipase producing halo tolerant Bacillus sp. VITL8 was isolated from oil contaminated areas of Vellore. The identity of the organism was established by 16S rDNA sequence, in addition to the morphological and biochemical characterization. The purified enzyme (22kDa, 8680U/mg) exhibited optimal activity at pH 7.0 and 40°C and retained more than 50% of its activity in the NaCl concentration range of 0-3.0M, pH 6.0-10.0 and 10-60°C. Secondary structure analysis, using circular dichroism, revealed that the enzyme is composed of 38% α-helix and 29% β-turns. The lipase activity significantly increased in the presence of (1mM) Mn(2+) (139%), Ca(2+) (134%) and Mg(2+) (130%). Organic solvents such as butanol and acetonitrile (25%, v/v) enhanced the activity whereas DMSO (25% v/v) retained the activity. The Km of enzyme-p-Nitrophenyl palmitate complex was determined to be 191μM with a Vmax of 68μM/mg/min. Though halotolerant Bacillus sp. has been explored for hydrocarbon degradation, to our knowledge this is the first report on the lipase activity of the isolate. The characteristics of the enzyme presented in this report, imply broader operational range of the enzyme and therefore could be suitable for many of the industrial chemical processes.

Screening, gene sequencing and characterising of lipase for methanolysis of crude palm oil

Staphylococcus sp. WL1 lipase (LipFWS) was investigated for methanolysis of crude palm oil (CPO) at moderate temperatures. Experiments were conducted in the following order: searching for the suitable bacterium for producing lipase from activated sludge, sequencing lipase gene, identifying lipase activity, then synthesising CPO biodiesel using the enzyme. From bacterial screening, one isolated specimen which consistently showed the highest extracellular lipase activity was identified as Staphylococcus sp. WL1 possessing lipFWS (lipase gene of 2,244 bp). The LipFWS deduced was a protein of 747 amino acid residues containing an α/β hydrolase core domain with predicted triad catalytic residues to be Ser474, His704 and Asp665. Optimal conditions for the LipFWS activity were found to be at 55 °C and pH 7.0 (in phosphate buffer but not in Tris buffer). The lipase had a K(M) of 0.75 mM and a V(max) of 0.33 mMmin(-1) on p-nitrophenyl palmitate substrate. The lyophilised crude LipFWS performed as good as the commonly used catalyst potassium hydroxide for methanolysis of CPO. ESI-IT-MS spectra indicated that the CPO was converted into biodiesel, suggesting that free LipFWS is a worthy alternative for CPO biodiesel synthesis.

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.

Influence of cultivation conditions on the production of a thermostable extracellular lipase from Amycolatopsis mediterranei DSM 43304

Among several lipase-producing actinomycete strains screened, Amycolatopsis mediterranei DSM 43304 was found to produce a thermostable, extracellular lipase. Culture conditions and nutrient source modification studies involving carbon sources, nitrogen sources, incubation temperature and medium pH were carried out. Lipase activity of 1.37 +/- 0.103 IU/ml of culture medium was obtained in 96 h at 28 degrees C and pH 7.5 using linseed oil and fructose as carbon sources and a combination of phytone peptone and yeast extract (5:1) as nitrogen sources. Under optimal culture conditions, the lipase activity was enhanced 12-fold with a twofold increase in lipase specific activity. The lipase showed maximum activity at 60 degrees C and pH 8.0. The enzyme was stable between pH 5.0 and 9.0 and temperatures up to 60 degrees C. Lipase activity was significantly enhanced by Fe(3+) and strongly inhibited by Hg(2+). Li(+), Mg(2+) and PMSF significantly reduced lipase activity, whereas other metal ions and effectors had no significant effect at 0.01 M concentration. A. mediterranei DSM 43304 lipase exhibited remarkable stability in the presence of a wide range of organic solvents at 25% (v/v) concentration for 24 h. These features render this novel lipase attractive for potential biotechnological applications in organic synthesis reactions.

Use of insoluble yeast β-glucan as a support for immobilization of Candida rugosa lipase

In the present study, insoluble yeast beta-glucan (IYG) has been explored as a support matrix for enzyme immobilization. IYG contains mainly beta-(1-3) linkages along with some intra- or inter-molecular branches of beta-(1-6) linkages with large number of free hydroxyl groups. Epichlorohydrin was used to convert these free hydroxyl groups into activated epoxy groups that are capable of forming covalent linkages with various groups of enzyme molecule. The epoxy-activated IYG was evaluated for immobilization of Candida rugosa lipase (CRL). Post-immobilization treatment of 5% glutaraldehyde was given in order to achieve stable and irreversible binding of enzyme on the support. The resultant biocatalytic IYG support expressed lipase activity of 8136.7 U/g and 59.6% activity yield. There was 51.05% retention of synthetic activity after six repeated esterification cycles, indicating its stability and reusability in non-aqueous medium. Moreover, the immobilized lipase gave the storage half-life of about 285 days (at 4 degrees C).

Lipolytic activity of Antarctic cold-adapted marine bacteria (Terra Nova Bay, Ross Sea)

AIMS

The aim of this study was to investigate the lipolytic activity of cold-adapted Antarctic marine bacteria and, furthermore, the combined effect of some environmental factors on this enzymatic process.

METHODS AND RESULTS

Strains were assayed for lipolytic activity on a basal medium amended with seven individual fatty acid esters. A significant activity was observed for 148 isolates (95.5% of the total screened). The interactive effect of pH, temperature and NaCl concentration on the substrates was tested for six representative isolates, identified as Pseudoalteromonas, Psychrobacter and Vibrio. Differences between strains according to NaCl and pH tolerances were observed. Only one strain degraded the substrate more efficiently at 4 degrees C than at 15 degrees C.

CONCLUSIONS

Our findings demonstrate that the lipolytic activity of Antarctic marine bacteria is rather variable, depending on culture conditions, and occurs in a wide range of salt concentration and pH.

SIGNIFICANCE AND IMPACT OF THE STUDY

Isolation and characterization of bacteria that are able to efficiently remove lipids at low temperatures will provide insight into the possibility to use cold-adapted bacteria as a source of exploitable enzymes. Moreover, research on the interactive effects of salt concentration, pH and temperature will be useful to understand the true enzyme potentialities for industrial applications.

Display of lipase on the cell surface ofEscherichia coli using OprF as an anchor and its application to enantioselective resolution in organic solvent

We have developed a new cell surface display system using a major outer membrane protein of Pseudomonas aeruginosa OprF as an anchoring motif. Pseudomonas fluorescens SIK W1 lipase gene was fused to the truncated oprF gene by C-terminal deletion fusion strategy. The truncated OprF-lipase fusion protein was successfully displayed on the surface of Escherichia coli. Localization of the truncated OprF-lipase fusion protein was confirmed by western blot analysis, immunofluorescence microscopy, and whole-cell lipase activity. To examine the enzymatic characteristics of the cell surface displayed lipase, the whole-cell enzyme activity and stability were determined under various conditions. Cell surface displayed lipase showed the highest activity at 37 degrees C and pH 8.0. It retained over 80% of initial activity after incubation for a week in both aqueous solution and organic solvent. When the E. coli cells displaying lipases were used for enantioselective resolution of racemic 1-phenylethanol in hexane, (R)-phenyl ethyl acetate was successfully obtained with the enantiomeric excess of greater than 96% in 36 h of reaction. These results suggest that E. coli cells displaying lipases using OprF as an anchoring motif can be employed for various biotechnological applications both in aqueous and nonaqueous phases.