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

Escherichia coli Surface Display: Advances and Applications in Biocatalysis

Escherichia coli surface display technology, which facilitates the stable display of target peptides and proteins on the bacterial surface through fusion with anchor proteins, has become a potent and versatile tool in biotechnology and biomedicine. The E. coli surface display strategy presents a unique alternative to classic intracellular and extracellular expression systems, facilitating the anchorage of target peptides and proteins on the cell surface for functional execution. This distinctive attribute also introduces a novel paradigm in the realm of biocatalysis, harnessing cells with surface-displayed enzymes to catalyze the conversion of substrates. This strategy effectively eliminates the requirement for enzyme purification, overcomes the limitations related to substrate transmembrane transport, improves enzyme activity and stability, and greatly reduces the cost of downstream product purification, thus making it widely used in biocatalysis. Here, we review recent advances in various surface display systems and surface display technology for biocatalytic applications. Additionally, we discuss the current limitations of this technology and several promising alternative display methods.

Biodegradation of combined pollutants of polyethylene terephthalate and phthalate esters by esterase-integrated Pseudomonas sp. JY-Q with surface-co-displayed PETase and MHETase

The waste pollution problem caused by polyethylene terephthalate (PET) plastics poses a huge threat to the environment and human health. As plasticizers, Phthalate esters (PAEs) are widely used in PET production and become combined pollutants with PET. Synthetic biology make it possible to construct engineered cells for microbial degradation of combined pollutants of PET and PAEs. PET hydroxylase (PETase) and monohydroxyethyl terephthalate hydroxylase (MHETase) isolated from Ideonella sakaiensis 201-F6 exhibit the capability to depolymerize PET. However, PET cannot enter cells, thus enzymatic degradation or cell surface displaying technology of PET hydrolase are the potential strategies. In this study, Pseudomonas sp. JY-Q was selected as a chassis strain, which exhibits robust stress tolerance. First, a truncated endogenous outer membrane protein cOmpA and its variant Signal (OprF)-cOmpA were selected as anchor motifs for exogenous protein to display on the cell surface. These anchor motifs were fused at the N-terminal of PET hydrolase and MHETase and transformed into Pseudomonas sp. JY-Q, the mutant strains successfully display the enzymes on cell surface, after verification by green fluorescent protein labeling and indirect immunofluorescence assay. The resultant strains also showed the catalytic activity of co-displaying PETase and MHETase for PET biodegradation. Then, the cell surface displaying PET degradation module was introduced to a JY-Q strain which genome was integrated with PAEs degrading enzymes and exhibited PAEs degradation ability. The resultant strain JY-Q-R1-R4-SFM-TPH have the ability of degradation PET and PAEs simultaneously. This study provided a promising strain resource for PET and PAEs pollution control.

Surface programmed bacteria as photo-controlled NO generator for tumor immunological and gas therapy

The use of bacteria as living vehicles has attracted increasing attentions in tumor therapy field. The combination of functional materials with bacteria dramatically facilitates the antitumor effect. Here, we presented a rationally designed living system formed by programmed Escherichia Coli MG1655 cells (Ec) and black phosphorus (BP) nanoparticles (NPs). The bacteria were genetically engineered to express tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), via an outer membrane YiaT protein (Ec-T). The Ec-T cells were associated with BP NPs on their surface to acquire BP@Ec-T. The designed living system could transfer the photoelectrons produced by BP NPs after laser irradiation and triggered the reductive metabolism of nitrate to nitric oxide for the in situ release at tumor sites, facilitating the therapeutic efficacy and the polarization of tumor associated macrophages to M1 phenotype. Meanwhile, the generation of reactive oxygen species induced the immunogenic cell death to further improve the antitumor efficacy. Additionally, the living system enhanced the immunological effect by promoting the apoptosis of tumor cells, activating the effect of T lymphocytes and releasing the pro-inflammatory cytokines. The integration of BP NPs, MG1655 cells and TRAIL led to an effective tumor therapy. Our work established an approach for the multifunctional antitumor living therapy.

Hydrophobic cell surface display system of PETase as a sustainable biocatalyst for PET degradation

Remarkably, a hydrolase from Ideonella sakaiensis 201-F6, termed PETase, exhibits great potential in polyethylene terephthalate (PET) waste management due to it can efficiently degrade PET under moderate conditions. However, its low yield and poor accessibility to bulky substrates hamper its further industrial application. Herein a multigene fusion strategy is introduced for constructing a hydrophobic cell surface display (HCSD) system in Escherichia coli as a robust, recyclable, and sustainable whole-cell catalyst. The truncated outer membrane hybrid protein FadL exposed the PETase and hydrophobic protein HFBII on the surface of E. coli with efficient PET accessibility and degradation performance. E. coli containing the HCSD system changed the surface tension of the bacterial solution, resulting in a smaller contact angle (83.9 ± 2° vs. 58.5 ± 1°) of the system on the PET surface, thus giving a better opportunity for PETase to interact with PET. Furthermore, pretreatment of PET with HCSD showed rougher surfaces with greater hydrophilicity (water contact angle of 68.4 ± 1° vs. 106.1 ± 2°) than the non-pretreated ones. Moreover, the HCSD system showed excellent sustainable degradation performance for PET bottles with a higher degradation rate than free PETase. The HCSD degradation system also had excellent stability, maintaining 73% of its initial activity after 7 days of incubation at 40°C and retaining 70% activity after seven cycles. This study indicates that the HCSD system could be used as a novel catalyst for efficiently accelerating PET biodegradation.

Towards synthetic PETtrophy: Engineering Pseudomonas putida for concurrent polyethylene terephthalate (PET) monomer metabolism and PET hydrolase expression

BACKGROUND

Biocatalysis offers a promising path for plastic waste management and valorization, especially for hydrolysable plastics such as polyethylene terephthalate (PET). Microbial whole-cell biocatalysts for simultaneous PET degradation and growth on PET monomers would offer a one-step solution toward PET recycling or upcycling. We set out to engineer the industry-proven bacterium Pseudomonas putida for (i) metabolism of PET monomers as sole carbon sources, and (ii) efficient extracellular expression of PET hydrolases. We pursued this approach for both PET and the related polyester polybutylene adipate co-terephthalate (PBAT), aiming to learn about the determinants and potential applications of bacterial polyester-degrading biocatalysts.

RESULTS

P. putida was engineered to metabolize the PET and PBAT monomer terephthalic acid (TA) through genomic integration of four tphII operon genes from Comamonas sp. E6. Efficient cellular TA uptake was enabled by a point mutation in the native P. putida membrane transporter MhpT. Metabolism of the PET and PBAT monomers ethylene glycol and 1,4-butanediol was achieved through adaptive laboratory evolution. We then used fast design-build-test-learn cycles to engineer extracellular PET hydrolase expression, including tests of (i) the three PET hydrolases LCC, HiC, and IsPETase; (ii) genomic versus plasmid-based expression, using expression plasmids with high, medium, and low cellular copy number; (iii) three different promoter systems; (iv) three membrane anchor proteins for PET hydrolase cell surface display; and (v) a 30-mer signal peptide library for PET hydrolase secretion. PET hydrolase surface display and secretion was successfully engineered but often resulted in host cell fitness costs, which could be mitigated by promoter choice and altering construct copy number. Plastic biodegradation assays with the best PET hydrolase expression constructs genomically integrated into our monomer-metabolizing P. putida strains resulted in various degrees of plastic depolymerization, although self-sustaining bacterial growth remained elusive.

CONCLUSION

Our results show that balancing extracellular PET hydrolase expression with cellular fitness under nutrient-limiting conditions is a challenge. The precise knowledge of such bottlenecks, together with the vast array of PET hydrolase expression tools generated and tested here, may serve as a baseline for future efforts to engineer P. putida or other bacterial hosts towards becoming efficient whole-cell polyester-degrading biocatalysts.

Effectively auto-regulated adsorption and recovery of rare earth elements via an engineered E. coli

Conventional mining processes of rare earth elements (REEs) usually produce REEs-rich industrial waterwastes, which leads to a significant waste of REEs resources and causes serious environmental pollution. Biosorption using engineered microorganisms is an attractive technology for the recovery of REEs from aqueous solution. To regulate the REEs' adsorption and recovery by sensing extraneous REEs, an engineered cascaded induction system, pmrCAB operon containing a lanthanide-binding tag (LBT) for sensing REEs, was incorporated into E. coli in conjunction with a silica-binding protein (Si-tag) and dLBT anchored onto the cell membrane. The sensing and adsorption capacities for Terbium (Tb), a typical study subject of REEs, were enhanced by screening an effective LBT and increasing the dLBT copy number. The adsorption capacity for Tb reached the highest reported value of 41.9 mgg^-1 dry cell weight (DCW). After adhering the engineered cells onto the silica column surface through overexpressed Si-tag, a high recovering efficiency (> 90%) of Tb desorption could be obtained with 3 bed volumes of citrate solution. In addition, the engineered cells also possessed fairly good adsorption capacity of other tested REEs. Our findings showed that the recovery of REEs with high efficiency, selectivity and controllability from aqueous solution can be well achieved via specifically bio-engineered strains.

Yeast cell surface display of bacterial PET hydrolase as a sustainable biocatalyst for the degradation of polyethylene terephthalate

Enzymatic hydrolysis of polyethylene terephthalate (PET) is considered to be an environmentally friendly method for the recycling of plastic waste. Recently, a bacterial enzyme named IsPETase was found in Ideonella sakaiensis with the ability to degrade amorphous PET at ambient temperature suggesting its possible use in recycling of PET. However, applying the purified IsPETase in large-scale PET recycling has limitations, i.e., a complicated production process, high cost of single-use, and instability of the enzyme. Yeast cell surface display has proven to be an effectual alternative for improving enzyme degradation efficiency and realizing industrial applications. This chapter deals with the construction and application of a whole-cell biocatalyst by displaying IsPETase on the surface of yeast (Pichia pastoris) cells.

Potential use of two aryl sulfotransferase cell-surface display systems to detoxify the endocrine disruptor bisphenol A

Bisphenol A (BPA) is one of the most common toxic endocrine disruptors in the environment. A fast, efficient and environmental-friendly method for BPA detoxification is urgently needed. In this study, we show that the enzymatic transformation of BPA into a non-estrogenic BPA sulfate can be performed by the aryl sulfotransferase (ASTB) from Desulfitobacterium hafniense. We developed and compared two Escherichia coli ASTB cell-surface displaying systems using the outer membrane porin F (OprF) and the lipoprotein outer membrane A (Lpp-OmpA) as carriers. The surface localization of both fusion proteins was confirmed by Western blot and flow cytometry analysis as well as the enzymatic activity assay of the outer membrane fractions. Unfortunately, Lpp-OmpA-ASTB cells had an adverse effect on cell growth. In contrast, the OprF-ASTB cell biocatalyst was stable, expressing 70% of enzyme activity for 7 days. It also efficiently sulfated 90% of 5 mM BPA (1 mg/mL) in wastewater within 6 h.

Novel Bacterial Surface Display System Based on the Escherichia coli Protein MipA

Bacterial surface display systems have been developed for various applications in biotechnology and industry. Particularly, the discovery and design of anchoring motifs is highly important for the successful display of a target protein or peptide on the surface of bacteria. In this study, an efficient display system on Escherichia coli was developed using novel anchoring motifs designed from the E. coli mipA gene. Using the C-terminal fusion system of an industrial enzyme, Pseudomonas fluorescens lipase, six possible fusion sites, V¹⁴⁰, V¹⁷⁶, K¹⁷⁹, V²²⁶, V²³², and K²³⁴, which were truncated from the C-terminal end of the mipA gene (MV¹⁴⁰, MV¹⁷⁶, MV¹⁷⁹, MV²²⁶, MV²³², and MV²³⁴) were examined. The whole-cell lipase activities showed that MV¹⁴⁰ was the best among the six anchoring motifs. Furthermore, the lipase activity obtained using MV¹⁴⁰ as the anchoring motif was approximately 20-fold higher than that of the previous anchoring motifs FadL and OprF but slightly higher than that of YiaTR232. Western blotting and confocal microscopy further confirmed the localization of the fusion lipase displayed on the E. coli surface using the truncated MV¹⁴⁰. Additionally the MV¹⁴⁰ motif could be used for successfully displaying another industrial enzyme, α-amylase from Bacillus subtilis. These results showed that the fusion proteins using the MV¹⁴⁰ motif had notably high enzyme activities and did not exert any adverse effects on either cell growth or outer membrane integrity. Thus, this study shows that MipA can be used as a novel anchoring motif for more efficient bacterial surface display in the biotechnological and industrial fields.

Cell Surface Display of Poly(3-hydroxybutyrate) Depolymerase and its Application

We have expressed extracellular poly(3-hydroxybutyrate) (PHB) depolymerase of Ralstonia pickettii T1 on the Escherichia coli surface using Pseudomonas OprF protein as a fusion partner by C-terminal deletion-fusion strategy. Surface display of depolymerase was confirmed by flow cytometry, immunofluorescence microscopy and whole cell hydrolase activity. For the application, depolymerase was used as an immobilized catalyst of enantioselective hydrolysis reaction for the first time. After 48 h, (R)-methyl mandelate was completely hydrolyzed, and (S)-mandelic acid was produced with over 99% enantiomeric excess. Our findings suggest that surface displayed depolymerase on E. coli can be used as an enantioselective biocatalyst.

Immunogenicity and protective efficacy of orally administered recombinant Lactobacillus plantarum expressing VP2 protein against IBDV in chicken

AIM

To develop an effective oral vaccine against the very virulent infectious bursal disease virus (vvIBDV), we generated two recombinant Lactobacillus plantarum strains (pPG612-VP2/LP and pPG612-T7g10-VP2/LP, which carried the T7g10 translational enhancer) that displayed the VP2 protein on the surface, and compared the humoral and cellular immune responses against vvIBDV in chickens.

METHODS AND RESULTS

We genetically engineered the L. plantarum strains pPG612-VP2/LP and pPG612-T7g10-VP2/LP constitutively expressing the VP2 protein of vvIBDV. We found that the T7g10 enhancer efficiently upregulates VP2 expression in pPG612-T7g10-VP2/LP. Orally administered, pPG612-T7g10-VP2/LP exhibited significant levels of protection (87·5%) against vvIBDV in chickens, indicating improved immunogenicity. Chickens in the pPG612-T7g10-VP2/LP group produced higher levels of interferons (IFN-γ) and interleukins (IL-2 and IL-4) than those in the pPG612-VP2/LP group. CD8+ and CD4+ lymphocyte counts indicated greater stimulation in the pPG612-T7g10-VP2/LP group (13·3 and 21·0% respectively) than in the pPG612-VP2/LP group (10·4 and 14·0% respectively). Thus, pPG612-T7g10-VP2/LP could induce strong humoral and cellular immune responses against vvIBDV.

CONCLUSIONS

The recombinant L. plantarum that expresses pPG612-T7g10-VP2 is a promising candidate for oral vaccine development against vvIBDV.

SIGNIFICANCE AND IMPACT OF THE STUDY

The recombinant Lactobacillus delivery system provides a promising strategy for vaccine development against vvIBDV in chickens.

Surface display for metabolic engineering of industrially important acetic acid bacteria

Acetic acid bacteria have unique metabolic characteristics that suit them for a variety of biotechnological applications. They possess an arsenal of membrane-bound dehydrogenases in the periplasmic space that are capable of regiospecific and enantioselective partial oxidations of sugars, alcohols, and polyols. The resulting products are deposited directly into the medium where they are easily recovered for use as pharmaceutical precursors, industrial chemicals, food additives, and consumer products. Expression of extracytoplasmic enzymes to augment the oxidative capabilities of acetic acid bacteria is desired but is challenging due to the already crowded inner membrane. To this end, an original surface display system was developed to express recombinant enzymes at the outer membrane of the model acetic acid bacterium Gluconobacter oxydans. Outer membrane porin F (OprF) was used to deliver alkaline phosphatase (PhoA) to the cell surface. Constitutive high-strength p264 and moderate-strength p452 promoters were used to direct expression of the surface display system. This system was demonstrated for biocatalysis in whole-cell assays with the p264 promoter having a twofold increase in PhoA activity compared to the p452 promoter. Proteolytic cleavage of PhoA from the cell surface confirmed proper delivery to the outer membrane. Furthermore, a linker library was constructed to optimize surface display. A rigid (EAAAK)₁ linker led to the greatest improvement, increasing PhoA activity by 69%. This surface display system could be used both to extend the capabilities of acetic acid bacteria in current biotechnological processes, and to broaden the potential of these microbes in the production of value-added products.

Some Gram-negative Lipoproteins Keep Their Surface Topology When Transplanted from One Species to Another and Deliver Foreign Polypeptides to the Bacterial Surface

In Gram-negative bacteria, outer membrane-associated lipoproteins can either face the periplasm or protrude out of the bacterial surface. The mechanisms involved in lipoprotein transport through the outer membrane are not fully elucidated. Some lipoproteins reach the surface by using species-specific transport machinery. By contrast, a still poorly characterized group of lipoproteins appears to always cross the outer membrane, even when transplanted from one organism to another. To investigate such lipoproteins, we tested the expression and compartmentalization in E. coli of three surface-exposed lipoproteins, two from Neisseria meningitidis (Nm-fHbp and NHBA) and one from Aggregatibacter actinomycetemcomitans (Aa-fHbp). We found that all three lipoproteins were lipidated and compartmentalized in the E. coli outer membrane and in outer membrane vesicles. Furthermore, fluorescent antibody cell sorting analysis, proteolytic surface shaving, and confocal microscopy revealed that all three proteins were also exposed on the surface of the outer membrane. Removal or substitution of the first four amino acids following the lipidated cysteine residue and extensive deletions of the C-terminal regions in Nm-fHbp did not prevent the protein from reaching the surface of the outer membrane. Heterologous polypeptides, fused to the C termini of Nm-fHbp and NHBA, were efficiently transported to the E. coli cell surface and compartmentalized in outer membrane vesicles, demonstrating that these lipoproteins can be exploited in biotechnological applications requiring Gram-negative bacterial surface display of foreign polypeptides.

Performance in synthetic applications of a yeast surface display-based biocatalyst

Organic synthesis with surface-displayed lipase: alkyl esters of fatty acids. Compared performance to commercial preparations. Catalyst is reusable and stable up to 50–60 °C. Kinetics of surface-displayed synthesis of butyl decanoate.

Characterization, performance, and applications of a yeast surface display-based biocatalyst

Yeast surface display (YSD) of two lipases. Measured expression level and copy number. Synthetic and hydrolytic activity comparable to commercial lipase. Cost analysis of YSD system vs. commercial formulations.

Enhanced production of ATP-binding cassette protein exporter-dependent lipase by modifying the growth medium components of Pseudomonas fluorescens

The industrially-important thermostable lipase, TliA, was extracellularly produced in the recombinant Pseudomonas fluorescens by the homologous expression of TliA and its cognate ABC protein exporter, TliDEF. To increase the secretory production of TliA, we optimized the growth temperature and the culture medium of P. fluorescens. The total amount and the specific productivity of lipase was highest at 25 °C of cell growth temperature, although maximal cell growth was observed at 30 °C. Using the culture medium composed of 20 g dextrin l(-1), 40 g Tween 80 l(-1) and 30 g peptone l(-1), TliA was produced at a level of 2,200 U ml(-1) in a flask culture. The TliA production increased about 3.8-fold (8,450 U ml(-1)) in batch fermentation using a 2.5 l fermentor, which was about 7.7-fold higher than that of previously reported TliA production.

Chromosomal insertions in the Lactobacillus casei upp gene that are useful for vaccine expression

To develop a stable and marker-free Lactobacillus strain useful for the expression of vaccines, we developed a temperature-sensitive suicide plasmid with expression cassettes containing an HCE promoter, a PgsA anchor, the alpha-toxin gene, and an rrnB T1T2 terminator (PPαT) that uses a 5-fluorouracil (5-FU) counterselectable marker for Lactobacillus casei. Three strains containing the correct PPαT expression cassettes were produced via the selective pressure of 5-FU screening. We confirmed that the upp gene was deleted and that the PPαT expression cassettes were inserted into the upp site of L. casei ATCC 393 by genomic PCR amplification and sequencing. 5-FU resistance in recombinant bacteria could be stably inherited for as long as 40 generations following insertion. However, bacteria containing the integrated DNA grew more slowly than wild-type L. casei. An indirect enzyme-linked immunosorbent assay (ELISA) analysis demonstrated that the alpha-toxin gene was expressed. Also, we visualized expression of the protein on the surface of L. casei cells using laser confocal microscopy. These results taken together demonstrate that these recombinant bacteria should provide a safe tool for effective vaccine production.

Autodisplay for the co-expression of lipase and foldase on the surface of E. coli: washing with designer bugs

BACKGROUND

Lipases including the lipase from Burkholderia cepacia are in a main focus in biotechnology research since many years because of their manifold possibilities for application in industrial processes. The application of Burkholderia cepacia lipase for these processes appears complicated because of the need for support by a chaperone, the lipase specific foldase. Purification and reconstitution protocols therefore interfere with an economic implementation of such enzymes in industry. Autodisplay is a convenient method to express a variety of passenger proteins on the surface of E. coli. This method makes subsequent purification steps to obtain the protein of interest unnecessary. If enzymes are used as passengers, the corresponding cells can simply be applied as whole cell biocatalysts. Furthermore, enzymes surface displayed in this manner often acquire stabilization by anchoring within the outer membrane of E. coli.

RESULTS

The lipase and its chaperone foldase from B. cepacia were co-expressed on the surface of E. coli via autodisplay. The whole cell biocatalyst obtained thereby exhibited an enzymatic activity of 2.73 mU mL⁻¹ towards the substrate p-nitrophenyl palmitate when applied in an OD₅₇₈ =1. Outer membrane fractions prepared from the same culture volume showed a lipase activity of 4.01 mU mL⁻¹. The lipase-whole cell biocatalyst as well as outer membrane preparations thereof were used in a standardized laundry test, usually adopted to determine the power of washing agents. In this test, the lipase whole cell biocatalyst and the membrane preparation derived thereof exhibited the same lipolytic activity as the purified lipase from B. cepacia and a lipase preparation which is already applied in commercial washing agents.

CONCLUSIONS

Co-expression of both the lipase and its chaperone foldase on the surface of E. coli yields a lipid degrading whole cell biocatalyst. Therefore the chaperone supported folding process, absolutely required for the lipolytic activity appears not to be hindered by surface display. Furthermore, the cells and the membrane preparations appeared to be stable enough to endure a European standard laundry test and show efficient fat removal properties herein.

Preparation of sticky Escherichia coli through surface display of an adhesive catecholamine moiety

Mussels attach to virtually all types of inorganic and organic surfaces in aqueous environments, and catecholamines composed of 3,4-dihydroxy-l-phenylalanine (DOPA), lysine, and histidine in mussel adhesive proteins play a key role in the robust adhesion. DOPA is an unusual catecholic amino acid, and its side chain is called catechol. In this study, we displayed the adhesive moiety of DOPA-histidine on Escherichia coli surfaces using outer membrane protein W as an anchoring motif for the first time. Localization of catecholamines on the cell surface was confirmed by Western blot and immunofluorescence microscopy. Furthermore, cell-to-cell cohesion (i.e., cellular aggregation) induced by the displayed catecholamine and synthesis of gold nanoparticles on the cell surface support functional display of adhesive catecholamines. The engineered E. coli exhibited significant adhesion onto various material surfaces, including silica and glass microparticles, gold, titanium, silicon, poly(ethylene terephthalate), poly(urethane), and poly(dimethylsiloxane). The uniqueness of this approach utilizing the engineered sticky E. coli is that no chemistry for cell attachment are necessary, and the ability of spontaneous E. coli attachment allows one to immobilize the cells on challenging material surfaces such as synthetic polymers. Therefore, we envision that mussel-inspired catecholamine yielded sticky E. coli that can be used as a new type of engineered microbe for various emerging fields, such as whole living cell attachment on versatile material surfaces, cell-to-cell communication systems, and many others.

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.

Decolorization of industrial synthetic dyes using engineered Pseudomonas putida cells with surface-immobilized bacterial laccase

Background

Microbial laccases are highly useful in textile effluent dye biodegradation. However, the bioavailability of cellularly expressed or purified laccases in continuous operations is usually limited by mass transfer impediment or enzyme regeneration difficulty. Therefore, this study develops a regenerable bacterial surface-displaying system for industrial synthetic dye decolorization, and evaluates its effects on independent and continuous operations.

Results

A bacterial laccase (WlacD) was engineered onto the cell surface of the solvent-tolerant bacterium Pseudomonas putida to construct a whole-cell biocatalyst. Ice nucleation protein (InaQ) anchor was employed, and the ability of 1 to 3 tandemly aligned N-terminal repeats to direct WlacD display were compared. Immobilized WlacD was determined to be surface-displayed in functional form using Western blot analysis, immunofluorescence microscopy, flow cytometry, and whole-cell enzymatic activity assay. Engineered P. putida cells were then applied to decolorize the anthraquinone dye Acid Green (AG) 25 and diazo-dye Acid Red (AR) 18. The results showed that decolorization of both dyes is Cu²⁺- and mediator-independent, with an optimum temperature of 35°C and pH of 3.0, and can be stably performed across a temperature range of 15°C to 45°C. A high activity toward AG25 (1 g/l) with relative decolorization values of 91.2% (3 h) and 97.1% (18 h), as well as high activity to AR18 (1 g/l) by 80.5% (3 h) and 89.0% (18 h), was recorded. The engineered system exhibited a comparably high activity compared with those of separate dyes in a continuous three-round shake-flask decolorization of AG25/AR18 mixed dye (each 1 g/l). No significant decline in decolorization efficacy was noted during first two-rounds but reaction equilibriums were elongated, and the residual laccase activity eventually decreased to low levels. However, the decolorizing capacity of the system was easily retrieved via a subsequent 4-h cell culturing.

Conclusions

This study demonstrates, for the first time, the methodology by which the engineered P. putida with surface-immobilized laccase was successfully used as regenerable biocatalyst for biodegrading synthetic dyes, thereby opening new perspectives in the use of biocatalysis in industrial dye biotreatment.

Biotechnological applications of microbial proteomes

Advances in proteomic technologies have led to the creation of large-scale proteome databases that can be used to elucidate invaluable information on the dynamics of the metabolic, signaling and regulatory networks and to aid understanding of physiological changes. In particular, proteomics can have practical applications, for example, through the identification of proteins that may be potential targets for the biotechnology industry, and through the extension of our understanding of the physiological action of these proteins. In this review, we describe proteomic approaches for the discovery of targets that have potential biotechnological applications. These targets include promoters, chaperones, soluble fusion partners, anchoring motifs, and excretion fusion partners. In addition, we discuss the potential applications of proteomic techniques for the design of future bioprocesses and the optimization of existing ones. Successful applications of proteomic information have proven to have enormous value for both scientific and practical applications.

Enhanced display of lipase on the Escherichia coli cell surface, based on transcriptome analysis

A cell surface display system was developed using Escherichia coli OmpC as an anchoring motif. The fused Pseudomonas fluorescens SIK W1 lipase was successfully displayed on the surface of E. coli cells, and the lipase activity could be enhanced by the coexpression of the gadBC genes identified by transcriptome analysis.

Display of a thermostable lipase on the surface of a solvent-resistant bacterium, Pseudomonas putida GM730, and its applications in whole-cell biocatalysis

Background

Whole-cell biocatalysis in organic solvents has been widely applied to industrial bioprocesses. In two-phase water-solvent processes, substrate conversion yields and volumetric productivities can be limited by the toxicity of solvents to host cells and by the low mass transfer rates of the substrates from the solvent phase to the whole-cell biocatalysts in water.

Results

To solve the problem of solvent toxicity, we immobilized a thermostable lipase (TliA) from Pseudomonas fluorescens on the cell surface of a solvent-resistant bacterium, Pseudomonas putida GM730. Surface immobilization of enzymes eliminates the mass-transfer limitation imposed by the cell wall and membranes. TliA was successfully immobilized on the surface of P. putida cells using the ice-nucleation protein (INP) anchoring motif from Pseudomonas syrinage. The surface location was confirmed by flow cytometry, protease accessibility and whole-cell enzyme activity using a membrane-impermeable substrate. Three hundred and fifty units of whole-cell hydrolytic activity per gram dry cell mass were obtained when the enzyme was immobilized with a shorter INP anchoring motif (INPNC). The surface-immobilized TliA retained full enzyme activity in a two-phase water-isooctane reaction system after incubation at 37°C for 12 h, while the activity of the free form enzyme decreased to 65% of its initial value. Whole cells presenting immobilized TliA were shown to catalyze three representative lipase reactions: hydrolysis of olive oil, synthesis of triacylglycerol and chiral resolution.

Conclusion

In vivo surface immobilization of enzymes on solvent-resistant bacteria was demonstrated, and appears to be useful for a variety of whole-cell bioconversions in the presence of organic solvents.

Cell surface display of lipase in Pseudomonas putida KT2442 using OprF as an anchoring motif and its biocatalytic applications

We developed a new cell surface display system in Pseudomonas putida KT2442 using OprF, an outer membrane protein of Pseudomonas aeruginosa, as an anchoring motif in a C-terminal deletion-fusion strategy. The Pseudomonas fluorescens SIK W1 lipase gene was fused to two different C-terminal truncated OprF genes, and the fusion genes were cloned into the broad-host-range plasmid pBBR1MCS2 to make pMO164PL and pMO188PL. Plasmid pMO188PL allowed better display of lipase and thus was chosen for further study. The display of lipase on the surface of P. putida KT2442 was confirmed by Western blot analysis, immunofluorescence microscopy, and measurement of whole-cell lipase activity. The whole-cell lipase activity of recombinant P. putida KT2442 harboring pMO188PL was more than fivefold higher than that of recombinant Escherichia coli displaying lipase in the same manner. Cell surface-displayed lipase exhibited the highest activity at 47 degrees C and pH 9.0, and the whole-cell lipase activity was greater than 90% of the initial activity in organic solvents at 47 degrees C for 1 week. In a biocatalytic application, enantioselective resolution of 1-phenyl ethanol was carried out in an organic solvent. (R)-Phenyl ethyl acetate was successfully produced with 41.9% conversion and an enantiomeric excess of more than 99% in a 36-h reaction. These results suggest that the OprF anchor can be used for efficient display of proteins in P. putida KT2442 and consequently for various biocatalytic applications.

Surface display of transglucosidase onEscherichia coli by using the ice nucleation protein ofXanthomonas campestris and its application in glucosylation of hydroquinone

A surface anchoring motif using the ice nucleation protein (INP) of Xanthomonas campestris pv. campestris BCRC 12,846 for display of transglucosidase has been developed. The transglucosidase gene from Xanthomonas campestris pv. campestris BCRC 12,608 was fused to the truncated ina gene. This truncated INP consisting of N- and C-terminal domains (INPNC) was able to direct the expressed transglucosidase fusion protein to the cell surface of E. coli with apparent high enzymatic activity. The localization of the truncated INPNC-transglucosidase fusion protein was examined by Western blot analysis and immunofluorescence labeling, and by whole-cell enzyme activity in the glucosylation of hydroquinone. The glucosylation reaction was carried out at 40 degrees C for 1 h, which gave 23 g/L of alpha-arbutin, and the molar conversion based on the amount of hydroquinone reached 83%. The use of whole-cells of the wild type strain resulted in an alpha-arbutin concentration of 4 g/L and a molar conversion of 16% only under the same conditions. The results suggested that E. coli displaying transglucosidase using truncated INPNC as an anchoring motif can be employed as a whole-cell biocatalyst in glucosylation.

Display of active enzymes on the cell surface of Escherichia coli using PgsA anchor protein and their application to bioconversion

We have developed a novel Escherichia coli cell surface display system by employing PgsA as an anchoring motif. In our display system, C-terminal fusion to PgsA anchor protein from Bacillus subtilis was used. The enzymes selected for display were alpha-amylase (AmyA) from Streptococcus bovis 148 and lipase B (CALB) from Candida antarctica. The molecular mass values of AmyA and CALB are approximately 77 and 34 kDa, respectively. The enzymes were displayed on the surface as a fusion protein with a FLAG peptide tag at the C terminus. Both the PgsA-AmyA-FLAG and PgsA-CALB-FLAG fusion proteins were shown to be displayed by immunofluorescence labeling using anti-FLAG antibody. The displayed enzymes were active forms, and AmyA and CALB activities reached 990 U/g (dry cell weight) and 4.6 U/g (dry cell weight), respectively. AmyA-displaying E. coli cells grew utilizing cornstarch as the sole carbon source, while CALB-displaying E. coli cells catalyzed enantioselective transesterification, indicating that they are effective whole-cell biocatalysts. Since a target enzyme with a size of 77 kDa and an industrially useful lipase have been successfully displayed on the cell surface of E. coli for the first time, PgsA protein is probably a useful anchoring motif to display various enzymes.