Enzymes with new biochemical properties in the pectinolytic complex produced by Aspergillus niger MIUG 16

Effect of microbial biostimulants on the antioxidant profile, antioxidant capacity and activity of enzymes influencing the quality level of raspberries (Rubus idaeus L.)

The influence of four microbial biostimulants containing various strains of Bacillus subtilis and/or Paenibacillus sp. on the quality of raspberries cv. Delniwa, Poemat, and Enrosadira cultivated in two consecutive seasons was investigated. The biostimulants influenced the antioxidant level, antioxidant capacity, phenolic acids and flavonoids profiles, enzymatic activity, and the degree of methylation and acetylation of the pectin in the raspberry fruits. The biostimulants had the greatest effect on the antioxidant content (16% - 20% increase) and capacity in the Delniwa raspberry fruits from the first season. A positive correlation was found between the activity of the β-galactosidase enzyme and ferric reducing power. In the second season, a decrease in the activity of pectin esterase and α-L-arabinofuranosidase and an increase in the degree of methylation of pectin were noted. Our results suggest that the changes in raspberry quality were related to the type of biostimulant applied.

Improving the specific activity and stability of alkaline pectinase PEL3 through SpyTag/SpyCatcher cyclization

OBJECTIVES

PEL3, an alkaline pectinase, exhibited the highest activity among documented alkaline pectate lyases reported in our early study. Unfortunately, undesired thermal stability hampering its industrial application. The purpose of this study is to enhance the performance of wild-type PEL3 (W-PEL3) based on SpyTag/SpyCatcher-mediated cyclization.

RESULTS

The cyclized PEL3 (C-PEL3) was observed to fold correctly and generate a spatial conformation in a head-to-tail manner in E. coli. C-PEL3 exhibited comparable optimum pH and temperature to those of W-PEL3. Moreover, the catalytic activity of C-PEL3 increased by 23% compared to W-PEL3, and the k_cat/K_m of C-PEL3 was 1.5-fold greater than that of the W-PEL3. Importantly, C-PEL3 showed improved stability compared to W-PEL3. Firstly, C-PEL3 displayed a 65% increase in residual activity after treatment at 55 °C for 30 min. Secondly, C-PEL3 was prone to resist heat-induced protein aggregation. Thirdly, C-PEL3 exhibited metal ion stability. Circular dichroism analysis revealed that C-PEL3 was more capable of maintaining its secondary structures than W-PEL3 upon heat treatment.

CONCLUSIONS

C-PEL3, the initial example of a circular pectinase through SpyTag/SpyCatcher cyclization, exhibits superior performance and represents a highly encouraging contender for industrial utilization.

Improvement on Thermostability of Pectate Lyase and Its Potential Application to Ramie Degumming

In order to obtain a thermostable pectate lyase for ramie degumming, a rational design based on structural analysis was carried out on a novel pectate lyase (Pel419) derived from the Dickeya Dadantii DCE-01 for high-efficiency ramie degumming. A total of five potential amino acid sites were chosen to replace residues. Then, the mutant enzymes were subjected to the heterologous expressions in Escherichia coli and their enzymatic characteristics were determined. The optimal reaction temperature for the five mutants kept consistent with that for the wild type. The enzyme activity and thermal stability of mutant V52A were significantly improved. Meanwhile, the weight loss rate obtained by V52A with the best enzymatic characteristics in the ramie degumming process at 50 °C is comparable with that obtained by commercial cotton-ramie processing pectinases, indicating that V52A was a potential industrial enzyme that could be applied to large-scale ramie degumming. In this study, the biological functions of conservative residues of Pel419 were preliminarily explored. The mutant V52A with both enzymatic activity and improved heat resistance was acquired, providing a superior material for developing enzyme preparations of ramie degumming, and rendering an effective method for the rational design aiming to improve the thermostability of pectate lyase.

A Novel Endo-Polygalacturonase from Penicillium oxalicum: Gene Cloning, Heterologous Expression and Its Use in Acidic Fruit Juice Extraction

An endo-polygalacturonase (endo-PGase) exhibiting excellent performance during acidic fruit juice production would be highly attractive to the fruit juice industry. However, candidate endo-PGases for this purpose have rarely been reported. In this study, we expressed a gene from Penicillium oxalicum in Pichia pastoris. The recombinant enzyme PoxaEnPG28C had an optimal enzyme activity at pH 4.5 and 45°C and was stable at pH 3.0-6.5 and < 45°C. The enzyme had a specific activity of 4,377.65 ± 55.37 U/mg towards polygalacturonic acid, and the K_m and V_max values of PoxaEnPG28C were calculated as 1.64 g/l and 6127.45 U/mg, respectively. PoxaEnPG28C increased the light transmittance of orange, lemon, strawberry and hawthorn juice by 13.9 ± 0.3%, 29.4 ± 3.8%, 95.7 ± 10.2% and 79.8 ± 1.7%, respectively; it reduced the viscosity of the same juices by 25.7 ± 1.6%, 52.0 ± 4.5%, 48.2 ± 0.7% and 80.5 ± 2.3%, respectively, and it increased the yield of the juices by 24.5 ± 0.7%, 12.7 ± 2.2%, 48.5 ± 4.2% and 104.5 ± 6.4%, respectively. Thus, PoxaEnPG28C could be considered an excellent candidate enzyme for acidic fruit juice production. Remarkably, fruit juice production using hawthorn as an material was reported for the first time.

Partial Purification and Characterization of Exo-Polygalacturonase Produced by Penicillium oxalicum AUMC 4153

Pectinase enzymes are important industrial enzymes having considerable applications in several industries, especially in food processing. Pectinases contribute 25% of global food enzyme sales. Therefore, the demand for a commercial enzyme with desirable characteristics and low production costs has become one of the great targets. Hence, this study aims to produce exo-polygalacturonase (exo-PG) using local fungal isolate Penicillium oxalicum AUMC 4153 by utilizing sugar beet manufacturing waste (sugar beet pulp) as a sole raw carbon source under shaken submerged fermentation, which is purified and characterized to optimize enzyme biochemical properties for industrial application. The purity of the obtained exo-PG was increased by about 28-fold, and the final enzyme yield was 57%. The partially purified enzyme was active at a broad range of temperatures (30–60 °C). The optimum temperature and pH for the purified exo-PG activity were 50 °C and pH 5. The enzyme was stable at a range of pH 3 to 6 and temperature 30–50 °C for 210 min. The values for K_m and V_max were 0.67 mg/mL, with polygalacturonic acid as substrate and 6.13 µmole galacturonic acid/min/mg protein, respectively. It can be concluded that purified exo-PG production by P. oxalicum grown on sugar beet waste is a promising effective method for useful applications.

Complete genome sequence of Sphingobium sp. strain PAMC 28499 reveals a potential for degrading pectin with comparative genomics approach

BACKGROUND

Spingobium sp. PAMC 28499 is isolated from the glaciers of Uganda. Uganda is a unique region where hot areas and glaciers coexist, with a variety of living creatures surviving, but the survey on them is very poor. The genetic character and complete genome information of Sphingobium strains help with environmental studies and the development of better to enzyme industry.

OBJECTIVE

In this study, complete genome sequence of Spingobium sp. PAMC 28499 and comparative analysis of Spingobium species strains isolated from variety of the region.

METHODS

Genome sequencing was performed using PacBio sequel single-molecule real-time (SMRT) sequencing technology. The predicted gene sequences were functionally annotated and gene prediction was carried out using the program NCBI non-redundant database. And using dbCAN2 and KEGG data base were degradation pathway predicted and protein prediction about carbohydrate active enzymes (CAZymes).

RESULTS

The genome sequence has 64.5% GC content, 4432 coding protein coding genes, 61 tRNAs, and 12 rRNA operons. Its genome encodes a simple set of metabolic pathways relevant to pectin and its predicted degradation protein an unusual distribution of CAZymes with extracellular esterases and pectate lyases. CAZyme annotation analyses revealed 165 genes related to carbohydrate active, and especially we have found GH1, GH2, GH3, GH38, GH35, GH51, GH51, GH53, GH106, GH146, CE12, PL1 and PL11 such as known pectin degradation genes from Sphingobium yanoikuiae. These results confirmed that this Sphingobium sp. strain PAMC 28499 have similar patterns to RG I pectin-degrading pathway.

CONCLUSION

In this study, isolated and sequenced the complete genome of Spingobium sp. PAMC 28499. Also, this strain has comparative genome analysis. Through the complete genome we can predict how this strain can store and produce energy in extreme environment. It can also provide bioengineered data by finding new genes that degradation the pectin.

Origins and features of pectate lyases and their applications in industry

Pectate lyase treatment can be an alternative strategy of the chemical processing, which causes severe environmental pollution, and has been broadly studied and applied for diverse industrial applications including textile industry, beverage industry, pulp processing, pectic wastewater pretreatment, and oil extraction. This review gave a brief description of the origins, enzymatic characterizations, structure, and applications of pectate lyases (Pels). Most of the reported pectate lyases are originated from microorganisms with a small number of them from plants and animals. Due to the diverse environments that these microorganisms exist, Pels present diversified features, especially for the range of optimal pH and temperature. The diversified biochemical properties of Pels define their applications in different industries, and the applications of alkaline Pels on cotton bioscouring and ramie degumming in textile industry were focused in this review. This review also discussed the perspectives of the development and applications of Pels. KEY POINTS: • The first review on pectate lyase focusing on biotechnological applications. • Origins, features, structures, applications of pectate lyases reviewed. • Applications of alkaline Pels in textile industry demonstrated. • Perspectives on future development and applications of Pels discussed.

Discovery of Components Acting as the Obstacles in the Detection of Enteric Viruses from Berries

This study investigated the obstacles in detecting enteric viruses from berry fruits, which are on the one hand often associated with outbreaks of viral enteric disease, and on the other hand recognized as a challenging food matrix for molecular detection of enteric viruses. According to the ISO 15216 protocol, for soft fruit samples, virus extraction is by elution with agitation followed by precipitation with polyethylene glycol/NaCl. As a result, first, the phenolic content in the berry eluate was found to be weakly correlated with the detection of coliphage MS2 spiked in the berry samples. Second and more importantly, it was observed that the gel-like pellets formed after precipitation could entrap considerable portions of viruses from being further purified and recovered for detection, suggesting that the low virus detection sensitivity from berries is largely due to the pectin content with complicated chemical structures in the berry fruits. Future research is needed to solve this problem in a targeted way.

Improving the Catalytic Performance of Pectate Lyase Through Pectate Lyase/Cu3(PO4)2 Hybrid Nanoflowers as an Immobilized Enzyme

Pectate lyases (Pels) can be used in the textile industrial process for cotton scouring and ramie degumming, and its hydrolyzed products oligo galacturonic acid, are high-value added agricultural and health products. In our previous studies, an alkaline pectate lyase PEL168 mutant, PEL3, was obtained with improved specific activity and thermostability. Here, a facile and rapid method for preparing an immobilized PEL3-inorganic hybrid nanoflower was developed, as it could improve its biocatalytic performance. With 0.02 mg/mL (112.2 U/mL) PEL3 in PBS buffer, five different divalent ions, including Mn2+, Ca2+, Co2+, Zn2+, and Cu2+, were used as inorganic component. The results showed that PEL3/Cu3(PO4)2 hybrid nanoflowers presented the highest relative activity with 2.5-fold increase, compared to the free PEL3. X-ray diffraction analysis confirmed that the composition of PEL3/Cu3(PO4)2 hybrid nanoflowers were pectate lyase PEL3 and Cu3(PO4)2⋅5H2O. The optimum temperature and pH of PEL3/Cu3(PO4)2 hybrid nanoflowers were ascertained to be 55°C and pH 9.0, respectively, exhibiting subtle difference from the free PEL3. However, the PEL3/Cu3(PO4)2 hybrid nanoflowers maintained 33% residual activity after 24 h incubation at 55°C, while the free PEL3 completely lost its activity after 18 h incubation at 55°C. Furthermore, over 50% residual activity of the PEL3/Cu3(PO4)2 hybrid nanoflowers was remained, even after four times of repetitive utilization, demonstrating its promising stability for practical application.

Isolation of Polygalacturonase-Producing Bacterial Strain from Tomatoes (Lycopersicon esculentum Mill.)

Background

Polygalacturonase (EC 3.2.1.15) enzyme aids in microbial spoilage of fruits and vegetables. It is very important to find economical ways to producing the enzyme so as to achieve maximum yield in industries due to its use at different areas of production process.

Methods

Isolation of polygalacturonase-producing bacterial strain from tomatoes (Lycopersicon esculentum Mill.) was studied. Polygalacturonase-producing bacterial strains were isolated and screened from tomatoes stored at normal laboratory temperature (25 ± 2°C). They were identified based on their morphological, biochemical, and molecular characteristics. The enzyme produced was partially purified by the ammonium sulphate precipitation method. Molecular weights and optimum conditions for best enzyme activity were obtained by SDS PAGE technique.

Results

Five bacterial isolates resulted after screening. Bacterial strain code B5 showed highest polygalacturonase activity. Optimum conditions for polygalacturonase PEC B5 were maintained at pH 4.5; temperature 35°C; substrate concentration 0.3 mg/ml, and best activity at less than 5 min of heating. The enzyme PEC B5 was found to weigh 65 kDa and 50 kDa for crude and partially purified aliquots, respectively. The result of 16S rRNA gene sequencing revealed bacterial strain code B5 as Enterobacter tabaci NR146667 having 79% similarity with the NCBI GenBank.

Conclusion

Microorganisms should be developed for large-scale production of enzymes in developing countries.

Cold-active pectinolytic activity produced by filamentous fungi associated with Antarctic marine sponges

Background

Pectinase enzymes catalyze the breakdown of pectin, a key component of the plant cell wall. At industrial level, pectinases are used in diverse applications, especially in food-processing industry. Currently, most of the industrial pectinases have optimal activity at mesophilic temperatures. On the contrary, very little is known about the pectinolytic activities from organisms from cold climates such as Antarctica. In this work, 27 filamentous fungi isolated from marine sponges collected in King George Island, Antarctica, were screened as new source of cold-active pectinases.

Results

In semi-quantitative plate assays, 8 out 27 of these isolates showed pectinolytic activities at 15 °C and one of them, Geomyces sp. strain F09-T3-2, showed the highest production of pectinases in liquid medium containing pectin as sole carbon source. More interesting, Geomyces sp. F09-T3-2 showed optimal pectinolytic activity at 30 °C, 10 °C under the temperature of currently available commercial mesophilic pectinases.

Conclusion

Filamentous fungi associated with Antarctic marine sponges are a promising source of pectinolytic activity. In particular, pectinases from Geomyces sp. F09-T3-2 may be potentially suitable for biotechnological applications needing cold-active pectinases. To the best of our knowledge, this is the first report describing the production of pectinolytic activity from filamentous fungi from any environment in Antarctica.

Biological Function(s) and Application (s) of Pectin and Pectin Degrading Enzymes

Pectin is an integral part of plant cell wall and since centuries pectin extracted from plants is widely used in food and fruit juice processing. Moreover, in last half century, the applications have also invaded into many bio-processing applications such as pharmaceutical, bioenergy, textile, paper and tea processing. In these growing industries, the use of pectinases has grown with a significant amount i.e. approximately 10 % of total global enzyme market comes from pectinases. Herein comprehensive analyses of information related to structure and function of pectin in plant cell wall as well as structural classes of pectins have been discussed. The major function of pectin is in cementing the cellulose and hemicelluloses network, cell-cell adhesion and plant defence. Keeping the wide use of pectin in food industry and growing need of environment friendly technology for pectin extraction has accelerated the demand of pectin degrading enzymes (PDEs). PDEs are from three enzyme classes: carbohydrate esterases from CE8 and CE12 family, glycoside hydrolases from GH28 family and lyases from PL1, 2, 3, 9 and 10. We have reviewed the literature related to abundance and structure-function of these abovementioned enzymes from bacteria. From the current available literature, we found very limited information is present about thermostable PDEs. Hence, in future it could be a topic of study to gain the insight about structure-function of enzymes together with the expanded role of thermostable enzymes in development of bioprocesses based on these enzymes.

Production, purification and biochemical characterization of an exo-polygalacturonase from Aspergillus niger MTCC 478 suitable for clarification of orange juice

Polygalacturonases (PG) represent an important member of pectinases group of enzymes with immense industrial applications. A fungal strain Aspergillus niger MTCC478 was used for the production of polygalacturonase both under submerged and solid-state fermentation condition. Further its production was optimized under solid-state fermentation condition with media comprising of wheat bran and tea extract. Purification of an exo-PG was achieved by acetone precipitation (60-90%) and CM-cellulose column chromatography revealing 15.28-fold purification with a specific activity of 33.47 U/mg protein and 1.2% yield. A relative molecular mass of purified PG was approximately 124.0 kDa. The pH and temperature optimum was found to be 4 and 50 °C, respectively. The k cat and K m value for degradation of PGA by the purified enzyme was found to be 194 s-1 and 2.3 mg/mL, respectively. Cu2+ was found to enhance the PG activity while Ag+ completely inhibited the enzyme activity. The application of the purified PG in orange juice clarification was elucidated.

Purification and Biochemical and Kinetic Properties of an Endo-Polygalacturonase from the Industrial Fungus

An endo-polygalacturonase secreted by <i>Aspergillus sojae </i>was characterized after being purified to homogeneity from submerged cultures with orange peel as the sole carbon source by gel filtration and ion-exchange chromatographies. According to SDS-PAGE and analytical isoelectric focusing analyses, the enzyme presents a molecular weight of 47 kDa and pI value of 4.2. This enzyme exhibits considerable stability under highly acidic to neutral conditions (pH 1.5-6.5) and presents a half-life of 2 h at 50°C. Besides its activity towards pectin and polygalacturonic acid, the enzyme displays pectin-releasing activity, acting best in a pH range of 3.3-5.0. Thin-layer chromatographic analysis revealed that tri-galacturonate is the main enzymatic end product of polygalacturonic acid hydrolysis, indicating that it is an endo-polygalacturonase. The enzyme exhibits Michaelis-Menten kinetics, with K_M and V_MAX values of 0.134 mg/mL and 9.6 µmol/mg/min, respectively, and remained stable and active in the presence of SO₂, ethanol, and various cations assayed except Hg²⁺.

Effect of physicochemical parameters on the polygalacturonase of an Aspergillus sojae mutant using wheat bran, an agro-industrial waste, via solid-state fermentation

BACKGROUND

Polygalacturonases (PGs) are valuable enzymes of the food industry; therefore it is of great importance to discover new and GRAS PG-producing microbial strains. In this study, PG enzyme produced from a high PG activity producer mutant Aspergillus sojae using wheat bran at the flask scale under pre-optimized conditions of solid-state fermentation (SSF) was biochemically characterized.

RESULTS

The crude PG enzyme showed optimum activity in the pH range 4.0-5.0 and was stable in the pH range 3.0-7.0. The optimum temperature for the PG was 40 °C and it retained 99% of its activity at 50 °C. The mutant A. sojae PG could preserve more than 50% of its stability between 25 and 50 °C, both for 30 and 60 min, and was found to be stable in the presence of most of the tested compounds and metal ions. The inactivation energy (Ed ) was determined as 125.3 kJ mol(-1) . The enthalpy (ΔH*), free energy (ΔG*) and entropy (ΔS*) of inactivation were found to be stable with increasing temperature.

CONCLUSION

The mutant A. sojae PG could be suitable for the clarification (depectinization) of orange and grape juices and wine. © 2015 Society of Chemical Industry.

Enhanced production of pectinase by Aspergillus terreus NCFT 4269.10 using banana peels as substrate

Aspergillus terreus NCFT4269.10 was implemented in solid-state (SSF) and liquid static surface fermentation (LSSF) for biosynthesis of pectinase. Amongst various substrates, like, mustard oil cake, neem oil cake, groundnut oil cake, black gram peels, green gram peels, chickling vetch peels/grass pea peels wheat bran, pearl millet residues, finger millet waste, broken rice, banana peels (BP), apple pomace (AP) and orange peels, banana peel (Musa paradisiaca L.; Family: Musaceae) was most suitable for pectinase biosynthesis (LSSF: 400 ± 21.45 Uml⁻¹; SSF: 6500 ± 1116.21 Ug⁻¹). Optimization of process parameters using one-variable-at-a-time method revealed that an initial medium pH of 5.0 at 30 °C and 96 h of incubation along with mannitol, urea, ammonium persulfate and isoleucine have positive influence on pectinase production. Further, K⁺ (1 mM), Riboflavin (10 mg 100 ml⁻¹) and gibberellic acid (0.025 %, w/v) supported in enhanced pectinase production. Banana peels and AP at a ratio of 9:1, moisture content of 90 % with 2 % inoculum size were suitable combinations for production of pectinase. Similarly, 96 h of soaking time with 0.1 M phosphate buffer (pH 6.5) is essential for pectinase recovery. Purification to electrophoretic homogeneity revealed 1.42 fold purification with 8.08 % yield and a molecular weight of 24.6 kDa. Scaling up of various fermentation parameters and supplementing BP as the substrate for pectinase production with better recovery could make it promising for different industrial exploitation.

Characterization of a neutral pectin lyase produced by Oidiodendron echinulatum MTCC 1356 in solid state fermentation

A neutral pectin lyase produced by a new fungal strain Oidiodendron echinulatum MTCC 1356 under solid state fermentation using wheat bran as agro waste has been studied. The enzyme was purified by ammonium sulphate precipitation (30-60%), DEAE anion exchange and Sephadex G-100 column chromatographies. The SDS-PAGE and native PAGE revealed two bands of sizes 42 and 47 kDa. The enzyme was purified 37 fold with specific activity of 4.5 U/mg and 2.25% yield. The K(m) and V(max) values determined using citrus pectin were 1.2 mg/ml and 0.36 IU/min respectively. The pH and temperature optima were pH 7.0 and 50 °C, respectively. The pH stability was around 5.0 for 24 h at 20 °C. The purified enzyme retained maximum activity for 30 min upto 50 °C. The activation energy for thermal denaturation of the purified enzyme was found to be 60.0 kJ/Mol. The effects of various metal ions and protein inhibitors on enzyme activity have revealed total inhibition of the enzyme activity in the presence of Ag(+) and Cu(+) and KMnO(4) at 1 mM. The neutral pectin lyase showed retting of Crotalaria juncea fibre in the presence of EDTA.

Quality Attributes of Cupuaçu Juice in Response to Treatment with Crude Enzyme Extract Produced by Aspergillus japonicus 586

Cupuaçu (Theobroma grandiflorum Schum) is an Amazonian Basin native fruit whose fruit pulp is consumed as a juice which presents high density, viscosity, and turbidity. Pectic enzymes, usually yielded by microorganisms, are used to reduce the juice viscosity and turbidity. The present study aims to evaluate the use of pectic enzymes when processing cupuaçu juice. The cupuaçu juice was obtained by using Aspergillus japonicus 586 crude enzyme extract and incubation at 50°C with agitation (140 rpm) for one hour. Enzyme activities were determined, and the juices were evaluated as to their yield, turbidity, viscosity, and chemical composition. The juice produced by using crude enzyme extract presented higher soluble solids, reducing sugars, and lower viscosity and turbidity.

Production, Purification, and Characterization of Polygalacturonase from Mucor circinelloides ITCC 6025

Mucor circinelloides produced an extracellular polygalacturonase enzyme, the production of which was enhanced when various production parameters were optimized. Maximum polygalacturonase (PGase) activity was obtained in 48 h at 30°C and pH 4.0 with pectin methyl ester (1% w/v) as carbon source and a combination of casein hydrolysate (0.1% w/v) and yeast extract (0.1% w/v) as nitrogen source. The enzyme was purified to homogeneity (13.3-fold) by Sephacryl S-100 gel-filtration chromatography. Its molecular weight was 66 kDa on SDS-PAGE. The enzyme was found to have K_m and V_max values of 2.2 mM and 4.81 IU/ml at 0.1% to 0.5% (w/v) concentration of the substrate. The addition of phenolic acids (0.05 mM), metal ions such as Mn⁺², Co⁺², Mg⁺², Fe⁺³, Al⁺³, Hg⁺², and Cu⁺², and thiols had inhibitory effect on the enzyme. The enzyme showed maximum activity in the presence of polygalacturonic acid (0.1% w/v) at pH 5.5 and 42°C.

Arabidopsis thaliana cells: a model to evaluate the virulence of Pectobacterium carotovorum

Pectobacterium carotovorum are economically important plant pathogens that cause plant soft rot. These enterobacteria display high diversity world-wide. Their pathogenesis depends on production and secretion of virulence factors such as plant cell wall-degrading enzymes, type III effectors, a necrosis-inducing protein, and a secreted virulence factor from Xanthomonas spp., which are tightly regulated by quorum sensing. Pectobacterium carotovorum also present pathogen-associated molecular patterns that could participate in their pathogenicity. In this study, by using suspension cells of Arabidopsis thaliana, we correlate plant cell death and pectate lyase activities during coinfection with different P. carotovorum strains. When comparing soft rot symptoms induced on potato slices with pectate lyase activities and plant cell death observed during coculture with Arabidopsis thaliana cells, the order of strain virulence was found to be the same. Therefore, Arabidopsis thaliana cells could be an alternative tool to evaluate rapidly and efficiently the virulence of different P. carotovorum strains.

Hunting down fungal secretomes using liquid-phase IEF prior to high resolution 2-DE

The secreted proteins (secretome) of fungi play a key role in interactions of pathogenic and symbiotic fungi with plants. Using the plant pathogenic fungus Leptosphaeria maculans and symbiont Laccaria bicolor grown in culture, we have established a proteomic protocol for extraction, concentration and resolution of the fungal secretome. As no proteomic data were available on mycelium tissues from both L. maculans and L. bicolor, mycelial proteins were studied; they also helped verifying the purity of secretome samples. The quality of protein extracts was initially assessed by both 1-DE and 2-DE using first a broad pH range for IEF, and then narrower acidic and basic pH ranges, prior to 2-DE. Compared with the previously published protocols for which only dozens of 2-D spots were recovered from fungal secretome samples, up to approximately 2000 2-D spots were resolved by our method. MS identification of proteins along several pH gradients confirmed this high resolution, as well as the presence of major secretome markers such as endopolygalacturonases, beta-glucanosyltransferases, pectate lyases and endoglucanases. Shotgun proteomic experiments evidenced the enrichment of secreted protein within the liquid medium. This is the first description of the proteome of L. maculans and L. bicolor, and the first application of liquid-phase IEF to any fungal extracts.