Detection of polygalacturonase, pectin-lyase and pectin-esterase activities in a Saccharomyces cerevisiae strain

Pectinases Secretion by Saccharomyces cerevisiae: Optimization in Solid-State Fermentation and Identification by a Shotgun Proteomics Approach

A sequential design strategy was applied to optimize the secretion of pectinases by a Saccharomyces cerevisiae strain, from Brazilian sugarcane liquor vat, on passion fruit residue flour (PFRF), through solid-state fermentation (SSF). A factorial design was performed to determine the influence variables and two rotational central composite designs were executed. The validated experimental result was of 7.1 U mL⁻¹ using 50% PFRF (w/w), pH 5, 30 °C for 24 h, under static SSF. Polygalacturonase, pectin methyl esterase, pectin–lyase and pectate–lyase activities were 3.5; 0.08; 3.1 and 0.8 U mL⁻¹, respectively. Shotgun proteomics analysis of the crude extract enabled the identification of two pectin–lyases, one pectate–lyase and a glucosidase. The crude enzymatic extract maintained at least 80% of its original activity at pH values and temperatures ranging from 2 to 8 and 30 to 80 °C, respectively, over 60 min incubation. Results revealed that PFRF might be a cost-effective and eco-friendly substrate to produce pectinases. Statistical optimization led to fermentation conditions wherein pectin active proteins predominated. To the extent of our knowledge, this is the first study reporting the synthesis of pectate lyase by S. cerevisiae.

Wine phenolic profile altered by yeast: Mechanisms and influences

Grape phenolic compounds undergo various types of transformations during winemaking under the influences of yeasts, which further impacts the sensory attributes, thus the quality of wine. Understanding the roles of yeasts in phenolics transformation is important for controlling wine quality through fermentation culture selection. This literature review discusses the mechanisms of how yeasts alter the phenolic compounds during winemaking, summarizes the effects of Saccharomyces cerevisiae and non-Saccharomyces yeasts on the content and composition of phenolics in wine, and highlights the influences of mixed cultural fermentation on the phenolic profile of wine. Collectively, this paper aims to provide a deeper understanding on yeast-phenolics interactions and to identify the current literature gaps for future research.

Investigation of antioxidant and anticancer activities of unsaturated oligo-galacturonic acids produced by pectinase of Streptomyces hydrogenans YAM1

Pectin, a diverse carbohydrate polymer in plants consists of a core of α-1,4-linked D-galacturonic acid units, includes a vast portion of fruit and agricultural wastes. Using the wastes to produce beneficial compounds is a new approach to control the negative environmental impacts of the accumulated wastes. In the present study, we report a pectinase producing bacterium Streptomyces hydrogenans YAM1 and evaluate antioxidative and anticancer effects of the oligosaccharides obtained from pectin degradation. The production of oligosaccharides due to pectinase activity was detected by thin layer chromatography (TLC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Our results revealed that S. hydrogenans YAM1 can degrade pectin to unsaturated pectic oligo-galacturonic acids (POS) with approximately 93% radical scavenging activity in 20 mg/mL which it is more than 50% of the same concentration of pectin. Flow cytometric analysis revealed that MCF-7 cells viability decreased more than 32 and 92% following treatment with 6 and 20 mg/mL POS after 24 h, respectively. It is suggested that pectin degradation by S. hydrogenans YAM1 is not only a new approach to produce highly active compounds from fruit wastes, but also is an effective method to remove fibrous pollutants from different environments.

Draft Genome Sequence of Enterobacter kobei M4-VN, Isolated from Potatoes with Soft Rot Disease

Enterobacter kobei M4-VN, isolated from potatoes with soft rot disease in Vietnam, contains a total of 4,754,309 bp with 4,424 predicted coding sequences and a G+C content of 55.1%.

Pectin methylesterase activity of plant DUF538 protein superfamily

DUF538 (domain of unknown function 538) proteins are known as a group of putative hypothetical proteins in a wide range of plant species. They have been identified from some plants challenged with various environmental stresses. However, a little is known about their functional properties. They have been newly predicted to have binding capacity and esterase-type hydrolytic activity towards bacterial lipopolysaccharides and chlorophyll molecules as carboxylic compounds in plants. In the present study, the binding ability and the methylesterase activity of DUF538 proteins towards pectin molecules were also predicted. Their similarities to pectin methylesterases and their binding ability to pectin molecule were predicted using bioinformatic tools as well as the experimental method. A probable cooperation was speculated between DUF538 and pectin methylesterase protein families in cell wall associated defense responses in plants.

Commercial Saccharomyces cerevisiae Yeast Strains Significantly Impact Shiraz Tannin and Polysaccharide Composition with Implications for Wine Colour and Astringency

To gain knowledge on the role of Saccharomyces cerevisiae yeast strains (and their hybrids) on wine sensory properties, 10 commercially available yeast strains were selected on the basis of their widespread usage and/or novel properties and used to produce Shiraz wines. Significant differences were evident post-alcoholic fermentation and after 24 months of ageing with regards to the number of wine compositional variables, in particular the concentration of tannin and polysaccharide. Strain L2323 is known for its pectinolytic activity and yielded the highest concentration of both yeast- and grape-derived polysaccharides. Wines made with the mannoprotein-producing strain Uvaferm HPS (high levels of polysaccharides) did not have elevated concentrations of yeast-derived polysaccharides, despite this observation being made for corresponding model fermentations, suggesting that mannoprotein production or retention might be limited by the wine matrix. Wine tannin concentration showed a high level of variability between strains, with L2323 having the highest, and AWRI1503 the lowest concentration. Sensory analysis of the wines after 24 months ageing revealed significant differences between the yeast strains, but only the attributes opacity (visual colour) and astringency could be predicted by partial least squares regression using the wine compositional data. Notably, the astringency attribute was associated with higher concentrations of both tannin and polysaccharide, contrary to reports in the literature which suggested that polysaccharide exerts a moderating effect on astringency. The results confirm previous reports demonstrating that the choice of yeast strain represents an opportunity to shape wine style outcomes.

Methanol contamination in traditionally fermented alcoholic beverages: the microbial dimension

Incidence of methanol contamination of traditionally fermented beverages is increasing globally resulting in the death of several persons. The source of methanol contamination has not been clearly established in most countries. While there were speculations that unscrupulous vendors might have deliberately spiked the beverages with methanol, it is more likely that the methanol might have been produced by contaminating microbes during traditional ethanol fermentation, which is often inoculated spontaneously by mixed microbes, with a potential to produce mixed alcohols. Methanol production in traditionally fermented beverages can be linked to the activities of pectinase producing yeast, fungi and bacteria. This study assessed some traditional fermented beverages and found that some beverages are prone to methanol contamination including cachaca, cholai, agave, arak, plum and grape wines. Possible microbial role in the production of methanol and other volatile congeners in these fermented beverages were discussed. The study concluded by suggesting that contaminated alcoholic beverages be converted for fuel use rather than out rightly banning the age—long traditional alcohol fermentation.

Occallatibacter riparius gen. nov., sp. nov. and Occallatibacter savannae sp. nov., acidobacteria isolated from Namibian soils, and emended description of the family Acidobacteriaceae

Three Gram-negative, non-spore-forming, encapsulated bacteria were isolated from a Namibian river-bank soil (strains 277T and 307) and a semiarid savannah soil (strain A2-1cT). 16S rRNA gene sequence analyses placed them within subdivision 1 of the Acidobacteria and revealed 100 % similarity between strains 277T and 307 and 98.2 % similarity between A2-1cT and the former two strains. The closest relatives with validly published names were Telmatobacter bradus, Acidicapsa borealis and Acidicapsa ligni (94.7-95.9 % similarity to the type strains). Cells of all three strains were rod-shaped and motile and divided by binary fission. Ultrastructural analyses revealed a thick cell envelope, resulting mainly from a thick periplasmic space. Colonies of strains 277T and 307 were white to cream and light pink, respectively, while strain A2-1cT displayed a bright pink colour. All three strains were aerobic, chemoheterotrophic mesophiles with a broad temperature range for growth and a moderately acidic pH optimum. Sugars and complex proteinaceous substrates were the preferred carbon and energy sources. A few polysaccharides were degraded. The major quinone in all three strains was MK-8; MK-7 occurred in strain A2-1cT as a minor compound. Major fatty acids were iso-C15 : 0 and iso-C17 : 1ω7c. In addition, iso-C17 : 0 occurred in significant amounts. The DNA G+C contents of strains 277T, 307 and A2-1cT were 59.6, 59.9 and 58.5 mol%, respectively. Based on these characteristics, the three isolates are assigned to two novel species of the novel genus Occallatibacter gen. nov., Occallatibacter riparius sp. nov. [type strain 277T ( = DSM 25168T = LMG 26948T) and reference strain 307 ( = DSM 25169 = LMG 26947)] and Occallatibacter savannae sp. nov. [type strain A2-1cT ( = DSM 25170T = LMG 26946T)]. Together with several other recently described taxa, the novel isolates provide the basis for an emended description of the established family Acidobacteriaceae.

Terriglobus albidus sp. nov., a member of the family Acidobacteriaceae isolated from Namibian semiarid savannah soil

A novel aerobic, chemo-organoheterotrophic bacterium, strain Ac_26_B10T, was isolated from a semiarid savannah soil collected in northern Namibia (Mashare, Kavango region). Based on analysis of its nearly full-length 16S rRNA gene sequence, the isolate belongs to the genus Terriglobus (family Acidobacteriaceae, order Acidobacteriales, class Acidobacteria) and shares 98.3 and 96.9 % 16S rRNA gene sequence similarity with its closest relatives, Terriglobus tenax DRP 35T and T. aquaticus O3SUJ4T. Cells were Gram-negative, coccoid to rod-shaped, non-motile and divided by binary fission. Strain Ac_26_B10T showed weak catalase activity and, in contrast to the other described species of the genus Terriglobus, was oxidase-positive. Compared with the already established species of the genus Terriglobus, the novel strain used a larger range of sugars and sugar alcohols for growth, lacked α-mannosidase activity and exhibited a higher temperature optimum of growth. DNA–DNA hybridization studies with its closest phylogenetic relative, T. tenax DSM 28898T, confirmed that strain Ac_26_B10T represents a distinct genomospecies. Its most abundant fatty acids were iso-C15 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and C16 : 0. Dominant polar lipids were phosphatidylethanolamine and diphosphatidylglycerol. The predominant menaquinone was MK-8; minor amounts of MK-7 and MK-8(H2) were also recorded. The G+C content of the genomic DNA was 58.5 mol%. On the basis of our polyphasic analysis, Ac_26_B10T represents a novel species of the genus Terriglobus, for which the name Terriglobus albidus sp. nov. is proposed. The type strain is Ac_26_B10T ( = DSM 26559T = LMG 27984T).

Evaluating the activity of the filamentous growth mitogen-activated protein kinase pathway in yeast

Mitogen-activated protein kinase (MAPK) pathways are evolutionarily conserved signaling pathways that regulate diverse processes in eukaryotes. One such pathway regulates filamentous growth, a nutrient limitation response in budding yeast and other fungal species. This protocol describes three assays used to measure the activity of the filamentous growth pathway. First, western blotting for phosphorylated (activated) MAPKs (P∼MAPKs; Slt2p, Kss1p, Fus3p, and Hog1p) provides a measure of MAPK activity in yeast and other fungal species. Second, the PGU1 gene is a transcriptional target of the filamentous growth pathway. Cells that undergo filamentous growth secrete Pgu1p, an endopolygalacturonase that degrades the plant-specific polysaccharide pectin. We describe an assay that measures secreted pectinase activity, which reflects an active filamentous growth pathway. Finally, in yeast, two mucin-like glycoproteins, Msb2 and Flo11, regulate filamentous growth. Secretion of the processed and shed glycodomain of Msb2 is an indicator of MAPK activity. Flo11, the major adhesion molecule that controls filamentous growth and biofilm/mat formation, is also shed from cells. Detecting shed mucins with epitope-tagged versions of the proteins (secretion profiling) provides information about the regulation of filamentous growth across fungal species.

Use of the Saccharomyces cerevisiae endopolygalacturonase promoter to direct expression in Escherichia coli

In Saccharomyces cerevisiae, an endopolygalacturonase encoded by the PGL1 gene catalyzes the random hydrolysis of the α-1,4 glycosidic linkages in polygalacturonic acid. To study the regulation of the PGL1 gene, we constructed a reporter vector containing the lacZ gene under the control of PGL1 promoter. Surprisingly, when Escherichia coli DH5α was transformed by this vector, cells harboring the constructed plasmid produced blue colonies. Sequence analysis of this promoter revealed that E. coli consensus sequences required to express an in-frame lacZ alpha product were present. We next decided to investigate how the PGL1 promoter is regulated in E. coli compared to yeast. In this study, we examined the modulation of the PGL1 promoter in E. coli, and the results indicated that its activity is greatly induced by saturated digalacturonic acid and is indirectly regulated by the transcriptional regulators the 2-keto-3-deoxygluconate repressor. Moreover, PGL1 expression is enhanced under aerobic conditions. We found that β-galactosidase activity in E. coli could reach 180 units, which is 40-fold greater than the activity produced in S. cerevisiae, and greater than recombinant protein expression previously reported by other researchers. We thus demonstrate that this vector can be considered as a dual expression plasmid for both E. coli and S. cerevisiae hosts. So far, no modulation of endoPG promoters expressed in E. coli has been reported.

Studies on the zymogram method for the detection of pectinolytic activities using CTAB

Zymogram analysis is a useful tool for the identification of several enzymes. The present study was undertaken to investigate the efficiency gains from the characterization of pectic enzymes on zymograms by staining of pectin-agarose overlays using cetyl trimethyl ammonium bromide also known as cetrimide or CTAB. The method is based on the fact that the enzymatic hydrolysis of the pectic substrates included in the agarose matrix gel inhibited their precipitation by CTAB, leading to the appearance of cleared zones in front of the pectin hydrolases and lyases. Conversely, esterases led to the increase of pectin precipitation. Fungal pectinolytic enzymes were separated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subjected to the zymogram detection technique, using two pectin substances, namely citrus pectin and polygalacturonic acid. Overall, the findings presented in the current study indicate that several elements (ions, salts, pH, temperature, chelators, and reducing agents) may significantly affect the results of zymogram analysis and can, therefore, be employed to enhance the discriminatory and operational potential of the analysis in terms of accurate discrimination between several pectinolytic activities involved and effective implementation of the purification procedures required in the process.

Determination of N-glycosylation site and glycan structures of pectin methylesterase in jelly fig (Ficus awkeotsang) Achenes

Pectin methylesterase (PME) in jelly fig (Ficus awkeotsang) achenes is an N-glycosylated enzyme responsible for the gelation of jelly curd. A recombinant jelly fig PME was overexpressed in Escherichia coli and confirmed by immunodetection and LC-nanoESI-MS/MS analysis. To identify the N-glycosylation site, native PME and its deglycosylated and recombinant forms, which lacked glycan, were purified and subjected to comparative MALDI-MS mapping of the corresponding tryptic fragments. The results showed that N-glycosylation occurred at Asn(153) of the mature jelly fig PME, the only glycosylation site predicted by its sequence analysis. The major N-glycans released from the native PME by PNGase F were identified by MS/MS analyses as xylosylated, noncore fucosylated pauci-mannose, and complex-type structures. Molecular modeling of the 3D structure of jelly fig PME indicated that the N-glycan was putatively attached to the back region of the active site of this enzyme.

The signaling mucins Msb2 and Hkr1 differentially regulate the filamentation mitogen-activated protein kinase pathway and contribute to a multimodal response

A central question in the area of signal transduction is why pathways utilize common components. In the budding yeast Saccharomyces cerevisiae, the HOG and filamentous growth (FG) MAPK pathways require overlapping components but are thought to be induced by different stimuli and specify distinct outputs. To better understand the regulation of the FG pathway, we examined FG in one of yeast's native environments, the grape-producing plant Vitis vinifera. In this setting, different aspects of FG were induced in a temporal manner coupled to the nutrient cycle, which uncovered a multimodal feature of FG pathway signaling. FG pathway activity was modulated by the HOG pathway, which led to the finding that the signaling mucins Msb2p and Hkr1p, which operate at the head of the HOG pathway, differentially regulate the FG pathway. The two mucins exhibited different expression and secretion patterns, and their overproduction induced nonoverlapping sets of target genes. Moreover, Msb2p had a function in cell polarization through the adaptor protein Sho1p that Hkr1p did not. Differential MAPK activation by signaling mucins brings to light a new point of discrimination between MAPK pathways.

Biochemical characterization of an extracellular polygalacturonase from Trichoderma harzianum

An extracellular polygalacturonase (PGII) from Trichoderma harzianum was purified to homogeneity by two chromatography steps using DEAE-Sepharose and Sephacryl S-200. The molecular weight of T. harzianum PGII was 31,000 Da by gel filtration and SDS-PAGE. PGII had isoelectric point of 4.5 and optimum pH of 5.0. PGII was very stable at the pH 5.0. The extent of hydrolysis of different pectins by enzyme was decreased with increasing of degree of esterification (DE). PGII had very low activity toward non-pectic polysaccharides. The apparent K(m) value and K(cat) value for hydrolyzing polygalacturonic acid (PGA) were 3.4 mg/ml and 592 s(-1), respectively. PGII was found to have temperature optimum at 40 degrees C and was approximately stable up to 30 degrees C for 60 min of incubation. All the examined metal cations showed inhibitory effects on the enzyme activity. A 1,10-phenanthroline, Tween 20, Tween 80, Triton X-100 and SDS had no effect on the enzyme activity. The rate of enzyme catalyzed reduction of viscosity of solutions of PGA or pectin was higher three times than the rate of release of reducing sugars indicating that the enzyme had an endo-action. The storage stability of the enzyme in liquid and powder forms was studied, where the activity of the powder form was stable up to 1 year. These properties of T. harzianum PGII with appreciable activity would be potentially novel source of enzyme for food processing.

Pectinolytic activity secreted by yeasts isolated from fermented citrus molasses

AIMS

The aim of this study was to obtain improved strains of pectinolytic yeasts adapted to the conditions of an industrial fermentation process, which was continuously operated to convert citrus molasses into ethanol.

METHODS AND RESULTS

The starter yeast of the industrial fermentation process was a commercial baker's yeast, which was capable of growing without forming any secretion halo of pectinase activity on solid medium. Nevertheless, isolates showing secretion of pectinolytic activity on plates were obtained from the fermentation process. The secretion of pectin-degrading activity by isolates on plates was repressed by galactose and improved as the result of colony aging on polygalacturonic acid plates at 30 degrees C. Liquefaction of polygalacturonate gels as well as the splitting of the pectin-degrading activity into a wall-linked and a supernatant fraction were also observed when the starter yeast was propagated under agitation in liquid medium containing pectin.

CONCLUSIONS

Isolates capable of secreting pectinolytic activity on plates were predominant at the end of the citrus molasses fermentation. Nevertheless, the sizes of the secretion haloes on plates were not necessarily an indication of the levels of pectinolytic activity secreted in the liquid medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

Improved pectinolytic strains of Saccharomyces can be used as a source of pectinases for a variety of applications. This organism also participates in plant deterioration processes.

Interactions between yeasts and grapevines: filamentous growth, endopolygalacturonase and phytopathogenicity of colonizing yeasts

It has been clearly established that phytopathogenic fungi, bacteria, and viruses exert biotic stresses on plants. Much less is known, however, about the interactions between enological species of yeast and their host plants. In a previous study, we described how Saccharomyces cerevisiae, the most common enological yeast, can act as a grapevine (Vitis vinifera L.) pathogen, causing growth retardation or plant death. In the present in vitro study on 11 strains of yeast belonging to different genera, which often occur on the surfaces of vineyard grapes and V. vinifera, a link was found to exist between strain phytopathogenecity and pseudohyphal growth habits and/or endopolygalacturonase activity. The results obtained here are consistent with earlier findings showing that the phytopathogenicity of yeast strains depends on the filamentous growth process, and show that endopolygalacturonase alone is not responsible for the invasion of plants tissues. The mechanisms observed here may be of significant ecological importance and may help to explain the long periods of yeast survival found to occur in vineyards.

Novel cross-linked alcohol-insoluble solid (CL-AIS) affinity gel from pea pod for pectinesterase purification

Alcohol-insoluble solids (AIS) from pea pod were cross-linked (CL-AIS) and used as an affinity gel matrix to isolate pectin esterases (PEs) from tendril shoots of chayote (TSC) and jelly fig achenes (JFA), and the results were compared with those isolated by ion-exchange chromatography with a commercial resin. CL-AIS gel matrix in a column displayed poor absorption and purification fold of PE; however, highly methoxylated CL-AIS (HM-CL-AIS), by exposing CL-AIS to methanolic sulfuric acid to increase the degree of esterification (DE) to 92%, facilitated the enzyme purification. The purified TSC PE and JFA PE by the HM-CL-AIS column were proofed as a single band on an SDS-PAGE gel, showing that the HM-CL-AIS column was a good matrix for purification of PE, either with alkaline isoelectric point (pI) (TSC PE) or with acidic pI (JFA PE).

Engineering of an oenological Saccharomyces cerevisiae strain with pectinolytic activity and its effect on wine

A pectinolytic industrial yeast strain of Saccharomyces cerevisiae was generated containing the S. cerevisiae endopolygalacturonase gene (PGU1) constitutively expressed under the control of the 3-phosphoglycerate kinase gene (PGK1) promoter. The new strain contains DNA derived exclusively from yeast and expresses a high polygalacturonic acid hydrolyzing activity. Yeast transformation was carried out by an integrative process targeting a dispensable upstream region of the acetolactate synthase locus (ILV2), which determines sulfometuron methyl resistance. Microvinification assays were performed on white and red musts with the transformed UCLMS-1M strain and with the same strain untransformed. It was found that the changes in the pectic polysaccharide contents did not directly affect the taste or flavor of the wine. From the data reported, it is deduced that the chief advantage of using the modified strain is that it improves the yield of must/wine extraction, while it also positively affects some variables relating to appearance.

Functional expression in pichia pastoris of an acidic pectin methylesterase from jelly fig (Ficus awkeotsang)

A cDNA fragment encoding an acidic pectin methylesterase (PME) of jelly fig achene was successfully expressed in Pichia pastoris under the control of the glyceraldehydes-3-phosphate dehydrogenase promoter. The recombinant PME was produced as a secretory protein by N-terminal fusion of a cleavable prepropeptide for signal trafficking, and thus easily harvested from the culture medium. Compared with native N-glycosylated PME (38 kDa) purified from jelly fig achenes, this recombinant PME (45 kDa) appeared to be hyperglycosylated. Activity staining indicated that the recombinant PME was functionally active. Yet the hyperglycosylated recombinant PME possessed thermostability and enzymatic capability over a broad pH range equivalent to those of the native PME. The success of functional production of this acidic jelly fig PME in P. pastoris has significantly broadened its applications in industry.

Endo-polygalacturonase in Saccharomyces wine yeasts: effect of carbon source on enzyme production

Eight wine yeast strains of Saccharomyces sp. were tested for polygalacturonase (PGase) activity, after cultivation on various carbon sources. No strain showed any activity when grown on glucose, while five strains produced PGase in the presence of galactose and polygalacturonate. These data suggest that the PGase of wine strains is repressed by glucose and induced by galactose and polygalacturonate. The existence of the PGase gene in the wine strains and its similarity with that of the laboratory strains was proved by Southern hybridization and PCR amplification. The promoter region of the PGase gene in the wine strains was slightly different from that of the laboratory strains. This possibly explains the different pattern of gene expression in wine and laboratory strains. The PGase of wine strains produced di- or tri-galacturonic acid from polygalacturonic acid, different from the fungal PGase.

Winemaking Biochemistry and Microbiology: Current Knowledge and Future Trends

The fermentation of grape must and the production of premium quality wines are a complex biochemical process that involves the interactions of enzymes from many different microbial species, but mainly yeasts and lactic acid bacteria. Yeasts are predominant in wine and carry out the alcoholic fermentation, while lactic acid bacteria are responsible for malolactic fermentation. Moreover, several optional winemaking techniques involve the use of technical enzyme preparations. Considerable progress has been made recently in understanding the biochemistry and interactions of enzymes during the winemaking process. In this study, some of these recent contributions in the biochemistry of winemaking are reviewed. This article intends to provide an updated overview (including works published until December, 2003) on the main biochemical and microbiological contributions of the different techniques that can be used in winemaking. As well as considering the transformations that take place in traditional winemaking, the production of special wines, such as sparkling wines, 'sur lie' wines, and biologically aged wines, are also studied.

Pectinolytic enzymes secreted by yeasts from tropical fruits

Three hundred yeasts isolated from tropical fruits were screened in relation to secretion of pectinases. Twenty-one isolates were able to produce polygalacturonase and among them seven isolates could secrete pectin lyase. None of the isolates was able to secrete pectin methylesterase. The pectinolytic yeasts identified belonged to six different genera. Kluyveromyces wickerhamii isolated from the fruit mangaba (Hancornia speciosa) secreted the highest amount of polygalacturonase, followed by K. marxianus and Stephanoascus smithiae. The yeast Debaryomyces hansenii produced the greatest decrease in viscosity while only 3% of the glycosidic linkages were hydrolysed, indicating that the enzyme secreted was an endo-polygalacturonase. The hydrolysis of pectin by polygalacturonase secreted by S. smithiae suggested an exo-splitting mechanism. The other yeast species studied showed low polygalacturonase activity.

Partially esterified oligogalacturonides are the preferred substrates for pectin methylesterase of Aspergillus niger

Investigations on the mode of action of Aspergillus niger pectin methylesterase (PME) towards differently C(6)- and C(1)-substituted oligogalacturonides (oligoGal p A) are described. De-esterification of methyl-esterified (un)saturated oligoGal p A proceeds via a specific pattern, depending on the degree of polymerization. Initially, a first methyl ester of the oligomer is hydrolysed, resulting in one free carboxyl group. Subsequently, this first product is preferred as a substrate and is de-esterified for a second time. This product is then accumulated and hereafter de-esterified further to the final product, i.e. oligoGal p A containing one methyl ester located at the non-reducing end residue for both saturated and unsaturated oligoGal p A, as found by post-source decay matrix-assisted laser-desorption/ionization-time-of-flight MS. The saturated hexamer is an exception to this: three methyl esters are removed very rapidly, instead of two methyl esters. When unsaturated oligoGal p A were used, the formation of the end product differed slightly, suggesting that the unsaturated bond at the non-reducing end influences the de-esterification process. In vivo, PME prefers methyl esters, but the enzyme appeared to be tolerant for other C(6)- and C(1)-substituents. Changing the type of ester (ethyl esterification) or addition of a methyl glycoside (C(1)) only reduced the activity or had no effect respectively. The specific product pattern was identical for all methyl- and ethyl-esterified oligoGal p A and methyl-glycosidated oligoGal p A, which strongly indicates that one or perhaps two non-esterified oligoGal p A are preferred in the active-site cleft.

Yeasts associated with fresh and frozen pulps of Brazilian tropical fruits

The occurrence of yeasts on ripe fruits and frozen pulps of pitanga (Eugenia uniflora L), mangaba (Hancornia speciosa Gom.), umbu (Spondias tuberosa Avr. Cam.), and acerola (Malpighia glaba L) was verified. The incidence of proteolytic, pectinolytic, and mycocinogenic yeasts on these communities was also determined. A total of 480 colonies was isolated and grouped in 405 different strains. These corresponded to 42 ascomycetous and 28 basidiomycetous species. Candida sorbosivorans, Pseudozyma antarctica, C. spandovensis-like, C. spandovensis, Kloeckera apis, C. parapsilosis, Rhodotorula graminis, Kluyveromyces marxianus, Cryptococcus laurentii, Metchnikowia sp (isolated only from pitanga ripe fruits), Issatchenkia occidentalis and C. krusei (isolated only from mangaba frozen pulps), were the most frequent species. The yeast communities from pitanga ripe fruits exhibited the highest frequency of species, followed by communities from acerola ripe fruits and mangaba frozen pulps. Yeast communities from frozen pulp and ripe fruits of umbu had the lowest number of species. Except the yeasts from pitanga, yeast communities from frozen pulp exhibited higher number of yeasts than ripe fruit communities. Mycocinogenic yeasts were found in all of the substrates studied except in communities from umbu ripe fruits and pitanga frozen pulps. Most of the yeasts found to produce mycocins were basidiomycetes and included P. antarctica, Cryptococcus albidus, C. bhutanensis-like, R. graminis and R. mucilaginosa-like from pitanga ripe fruits as well as black yeasts from pitanga and acerola ripe fruits. The umbu frozen pulps community had the highest frequency of proteolytic species. Yeasts able to hydrolyse casein at pH 5.0 represented 38.5% of the species isolated. Thirty-seven percent of yeast isolates were able to hydrolyse casein at pH 7.0. Pectinolytic yeasts were found in all of the communities studied, excepted for those of umbu frozen pulps. The highest frequency of pectinolytic activity was found in mangaba frozen pulp communities. Around 30% of all isolates produced pectinases. The ability to split arbutin was observed in all communities ranging from 8% in yeasts from pitanga frozen pulps to 40.6% in acerola ripe fruit communities. Among 432 species tested, 125 were active for beta-glucosidase production, and Kloeckera apis, P. antarctica, C. sorbosivorans, and C. spandovensis-like were the most active species.

Purification and glycosylation analysis of an acidic pectin methylesterase in jelly fig (Ficus awkeotsang) achenes

An acidic pectin methylesterase (PME) is responsible for the gelation of water extract from jelly fig (Ficus awkeotasang) achenes. A new, fast and efficient, method has been developed to purify this acidic PME. The method includes preparing jelly curd by traditional hand washing, extracting proteins from the curd, and separating PME by anion-exchanger. The purified PME exists as a monomer of 38 kDa determined by gel filtration, and exerts enzymatic activity over a broad pH range, particularly in acidic environments where most known PME enzymes from various species are inactivated. Chemical staining and enzymatic cleavage suggest that the jelly fig PME is an N-linked glycoprotein. Fluorophore-assisted carbohydrate electrophoresis reveals that the polysaccharide of this glycoprotein putatively consists of 22 hexoses including 16 mannose, 4 N-acetylglucosamine, and 2 galactose residues.

Mutagenesis of key amino acids alters activity of a Saccharomyces cerevisiae endo-polygalacturonase expressed in Pichia pastoris

A polygalacturonase (PG)-encoding gene from Saccharomyces cerevisiae (PGU1) was successfully expressed in the methylotrophic yeast Pichia pastoris. PG secretion was efficiently directed by the S. cerevisiae alpha-factor signal sequence, while the native (PGU1) leader peptide was unable to direct protein export in P. pastoris. The level of PGU1 activity achieved in P. pastoris was significantly enhanced when compared to activity using the same gene in S. cerevisiae. Expression of PG proteins, engineered by site-directed mutagenesis, in P. pastoris showed that aspartic acid residues at positions 179, 200, and 201, and histidine 222 were essential for enzyme activity. Mutation of the two potential glycosylation sites in PGU1 showed that the two residues individually (N318D, N330D) did not affect secreted enzyme activity, but the double mutant caused a 50% reduction in enzyme activity when compared to the wild-type PGU1 transformant.

Screening for the production of extracellular hydrolytic enzymes by non-Saccharomyces wine yeasts

AIMS

The objective of this study was to investigate what types of enzymes are being produced by non-Saccharomyces yeasts isolated from grapes in South Africa vineyards and clarified grape juice. These enzyme profiles could pave the way for attributing specific effects in wine to some of these enzymes produced by so-called wild yeasts associated with grape must.

METHODS AND RESULTS

In this study 245 yeast isolates, belonging to the genera Kloeckera, Candida, Debaryomyces, Rhodotorula, Pichia, Zygosaccharomyces, Hanseniaspora and Kluyveromyces were screened for the production of extracellular pectinases, proteases beta-glucanases, lichenases, beta-glucosidases, cellulases, xylanases, amylases and sulphite reductase activity. These yeasts, representing 21 species, were previously isolated from grapes and clarified grape juice. The production of all extracellular hydrolytic enzymes screened for was observed except beta-glucosidase activity. The amount and range of enzymes produced varied with different isolates of the same species.

CONCLUSION

This study clearly revealed the potential of non-Saccharomyces wine yeasts to produce a wide range of useful extracellular enzymes during the initial phase of wine fermentation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Enzymes produced by indigenous yeasts associated with grapes and juice might be harnessed to catalyse desired biotransformations during wine fermentation.