A comparison of -glucanase and -glucosidase in Saccharomyces lactis

Droplet digital microfluidic system for screening filamentous fungi based on enzymatic activity

Fungal cell-wall-degrading enzymes have great utility in the agricultural and food industries. These cell-wall-degrading enzymes are known to have functions that can help defend against pathogenic organisms. The existing methods used to discover these enzymes are not well adapted to fungi culture and morphology, which prevents the proper evaluation of these enzymes. We report the first droplet-based microfluidic method capable of long-term incubation and low-voltage conditions to sort filamentous fungi inside nanoliter-sized droplets. The new method was characterized and validated in solid-phase media based on colloidal chitin such that the incubation of single spores in droplets was possible over multiple days (2-4 days) and could be sorted without droplet breakage. With long-term culture, we examined the activity of cell-wall-degrading enzymes produced by fungi during solid-state droplet fermentation using three highly sensitive fluorescein-based substrates. We also used the low-voltage droplet sorter to select clones with highly active cell-wall-degrading enzymes, such as chitinases, β-glucanases, and β-N-acetylgalactosaminidases, from a filamentous fungi droplet library that had been incubated for >4 days. The new system is portable, affordable for any laboratory, and user-friendly compared to classical droplet-based microfluidic systems. We propose that this system will be useful for the growing number of scientists interested in fungal microbiology who are seeking high-throughput methods to incubate and sort a large library of fungal cells.

Biotransformation of mogrosides from Siraitia grosvenorii Swingle by Saccharomyces cerevisiae

Mogrosides are a group of triterpenoidal saponins from the fruit of Siraitia grosvenorii Swingle; they are intensely sweet and have consequently been used as a substitute for sugar by the food industry. The lack of efficient methods to produce specific mogrosides has hindered investigation of the relationship between their structure and bioactivity, e.g., down-regulation of blood glucose levels, anti-inflammation, and antiviral infection. Here, we attempt to selectively convert the major saponin mogroside V, a mogrol pentaglucoside, into mogroside III E, a triglucoside, via the β-glucosidases of the budding yeast Saccharomyces cerevisiae. We report that the β-glucopyranosyl and β-glucopyranosyl-(1→2)-β-d-glucopyranosyl attached on C-3 and -24 of mogrol, respectively, were resistant to hydrolysis by yeast β-d-glucosidases. We further screened 16 mutants bearing single defective glucanase or glucosidase genes, thereby demonstrating that Exg1 is a major enzyme of the initiation of mogroside V conversion. Deletion of the KRE6 gene unexpectedly facilitated the production of mogroside III E in yeast culture. This paper demonstrates that yeast knockout mutants are a valuable tool for saponin modification and for studying the specificity of glucosidase function.

Optimization of a rapid method for studying the cellular location of beta-glucosidase activity in wine yeasts

AIMS

To improve a method for determining beta-glucosidase activity and to apply it in yeasts isolated from wine ecosystems from "La Mancha" region and to know its cellular location.

METHODS AND RESULTS

A total of 82 wine yeasts were identified (PCR/RFLP) and evaluated for their beta-glucosidase activity. First, they were qualitatively evaluated by growth on YNB cellobiose, the activity was quantified using different culture media, under aerobic and anaerobic conditions and cells after 24-72 h of growth. To study the location activity, five fractions were obtained (supernatant, whole cell, cell wall, cytosol and cell membrane). The enzymatic assays were optimized, being: growth in YP cellobiose for 72 h in aeration conditions and, after cell removing, enzyme analysis with 128 g l(-1) of cellobiose as substrate, for 30 min at 30 degrees C. The genus that displayed the greatest activity were Pichia, Hanseniaspora and Rhodotorula, and the activity was intracellular.

CONCLUSIONS

The study showed that beta-glucosidase activity was induced by the carbon source and was aerobic dependent. The non-Saccharomyces species displayed the greatest activity, which was intracellular and strain-dependent.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study developed a reliable method for screening beta-glucosidase activity in yeasts isolated from wine ecosystems. This activity is very important in the release of monoterpenols from glycoside precursors for the enhancement of wine aromas.

Cloning and analysis of CoEXG1, a secreted 1,3-beta-glucanase of the yeast biocontrol agent Candida oleophila

Lytic enzymes may have a role in the biological control of fungi. The yeast biocontrol agent, Candida oleophila, is an excellent subject to research this matter. In the present study, CoEXG1, which encodes for a secreted 1,3-beta-glucanase, is the first gene to be cloned from C. oleophila. It was isolated from a partial genomic library and analysed. Its open reading frame and putative promoter were expressed in baker's yeast, Saccharomyces cerevisiae. The reading frame, expressed under the inducible GAL1 promoter, caused an increased secretion of beta-glucanase, and the putative promoter region activated the lacZ reporter gene, to which it was fused. Sequencing analysis revealed that CoEXG1 carries the signature pattern of the 5 glycohydrolases family and has a putative secretion leader, as well as a high degree of identity to yeast 1,3-beta-glucanases. The GenBank Accession No. of CoEXG1 is AF393806.

Cloning and characterization of the EXG1 gene from the yeast Yarrowia lipolytica

The YlEXG1 gene of Yarrowia lipolytica, encoding an exo-1, 3-beta-glucanase, was isolated by screening a genomic library with a DNA probe obtained by PCR amplification, using oligonucleotides designed according to conserved regions in the EXG1, EXG2 and SSG1 genes from Saccharomyces cerevisiae. YlEXG1 consists of a 1263 bp open reading frame encoding a protein of 421 amino acids with a calculated molecular weight of 48 209 Da. Northern blot analysis revealed a unique YlEXG1-specific transcript, 1.4 kb long. A putative pre(signal)-peptide of 15 amino acids is proposed at the N-terminal domain of the primary translation product. The deduced amino acid sequence shares a high degree of homology with exo-1, 3-beta-glucanases from other yeast species, including S. cerevisiae, Kluyveromyces lactis, Pichia angusta and Debaryomyces occidentalis. YlExg1p contains the invariant amino acid positions which have been shown to be important in the catalytic function of family 5 glycosyl hydrolases. Chromoblot analysis indicated that YlEXG1 is located on chromosome VI. Disruption of YlEXG1 did not result in a phenotype under laboratory conditions and did not prevent the yeast-hypha transition. The sequence data reported in this paper have been assigned EMBL Accession No. Z46872.

Cloning and characterization of 1,3-beta-glucanase-encoding genes from non-conventional yeasts

The molecular cloning of 1,3-beta-glucanase-encoding genes from different yeast species was achieved by screening genomic libraries with DNA probes obtained by PCR-amplification using oligonucleotides designed according to conserved regions in the EXG1, EXG2 and SSG1 genes from Saccharomyces cerevisiae. The nucleotide sequence of the KlEXG1 (Kluyveromyces lactis), HpEXG1 (Hansenula polymorpha) and SoEXG1 (Schwanniomyces occidentalis) genes was determined. K1EXG1 consists of a 1287 bp open reading frame encoding a protein of 429 amino acids (49,815 Da). HpEXG1 specifies a 435-amino acid polypeptide (49,268 Da) which contains two potential N-glycosylation sites. SoEXG1 encodes a protein of 425 residues (49,132 Da) which contains one potential site for N-linked glycosylation. Expression in S. cerevisiae of KlEXG1, SoEXG1 or HpEXG1 under control of their native promoters resulted in the secretion of active 1,3-beta-glucanases. Disruption of KlEXG1 did not result in a phenotype under laboratory conditions. Comparison of the primary translation products encoded by KlEXG1, HpEXG1 and SoEXG1 with the previously characterized exo-1,3-beta-glucanases from S. cerevisiae and C. albicans reveals that enzymes with this type of specificity constitute a family of highly conserved proteins in yeasts. KlExg1p, HpExg1p and SoExg1p contain the invariant amino acid positions which have been shown to be important in the catalytic function of family 5 glycosyl hydrolases.

The major exoglucanase from Candida albicans: a non-glycosylated secretory monomer related to its counterpart from Saccharomyces cerevisiae

Exoglucanases secreted by two different strains from Candida albicans have been purified to homogeneity. The purified enzyme from each strain behaved as a non-glycosylated monomer (molecular weight 38,000) that was identical in terms of sodium dodecyl sulphate/polyacrylamide gel electrophoresis comigration, amino acid analysis and amino terminal sequence. The amino acid composition was similar to that of the major exoglucanase from Saccharomyces cerevisiae. In addition, these two enzymes displayed a 50% homology in the first 35 amino acids of the amino terminus. Antibodies against the deglycosylated exoglucanase (treated with Endo H) from S. cerevisiae were reactive with the exoglucanase from C. albicans and vice versa. Immunoblotting proved to be a semiquantitative method to detect C. albicans antigen in culture fluids. The exoglucanase from C. albicans appears to enter the secretory pathway without undergoing N-glycosylation.

Detection of inactive precursors of beta-glucanases in Saccharomyces cerevisiae

Accumulation and secretion of beta-glucanases have been studied in vivo by using a thermosensitive secretory mutant of Saccharomyces cerevisiae blocked at the endoplasmic reticulum level (sec 18-1). When incubated at the restrictive temperature no accumulation of active glucanases was observed. Following a shift to permissive conditions in the presence of cycloheximide a rise in the internal activity took place. The increase in total glucanase activity was partially due to the activation of an exo-glucanase that hydrolyzes PNPG. It is concluded that glucanases are synthesized in inactive precursor forms and are converted to the active forms in their secretory pathway.

Saccharomyces cerevisiae mutant defective in exo-1,3-beta-glucanase production

Saccharomyces cerevisiae S288C produced two laminarinases (1,3-beta-glucanases) which were separated by diethylaminoethyl-Sephadex column chromatography; one was an endo-1,3-beta-glucanase, and the other was an exo-1,3-beta-glucanase active not only on laminarin but also on pustulan (1,6-beta-glucan) and on p-nitrophenyl-beta-D-glucoside. A mutant defective in the production of this last enzyme was isolated, and the mutation was named exb1-1. The selection procedure was based on the capacity of exo-1,3-beta-glucanase to hydrolyze synthetic glucosides. The level of endo-1,3-beta-glucanase in cell extracts of the mutant was normal, but the exo-1,3-beta-glucanase could not be detected by column chromatographic analysis of these extracts. The mutant phenotype, recessive in heterozygous diploids, was stable through successive meioses and showed a Mendelian segregation, indicating that the mutation affected a single gene, which was named EXB1. The lack of production of exo-1,3-beta-glucanase persisted through all the phases of growth, but growth itself was not impaired by the enzyme deficiency.

Regulation of the beta-1,3-glucanase system in Penicillium italicum: glucose repression of the various enzymes

The microscopic fungus Penicillium italicum when grown in a synthetic liquid medium produced at least three enzymes with beta-1,3-glucanase activity which were separated by diethylaminoethyl-Sephadex column chromatography. These were named beta-1,3-glucanases I, II, and III respective to their order of elution from the column. A tentative characterization of these three enzymes indicated that they have different modes of action; the first one is an endoglucanase, the second is an exoglucanase, and the third probably has both mechanisms of action. Glucose had a repressive effect on all three enzymes. Only small amounts of beta-1,3-glucanases II and III were present in the cells when they were actively growing in the presence of this sugar. However, when the cells were transferred to a medium low in glucose, a significant increase in the specific activity of beta-1,3-glucanase took place; this was due in part to a much more active production of beta-1,3-glucanases II and III and in part to the appearance of beta-1,3-glucanase I, which could only be detected after more than 12 h of incubation in this medium. The results are discussed in the context of possible beta-1,3-glucanase functions in the fungal cells.

Purification of some glycoside hydrolases by affinity chromatography

Two glycoproteins have been isolated from the cell walls of baker's yeast. One is a glucan-protein complex which has been partially characterised as having a branched carbohydrate structure composed of chains of (1 leads to 3)-linked beta-D-glucosyl residues, some of which are attached by (1 leads to 6)-linkages to the main chain. Immobilization of this glycoprotein was achieved by covalent attachment to Sepharose, and the product was used to isolate a number of (1 leads to 3)-beta-D-glucan hydrolases from Helix pomatia, malted barley, and Basidiomycete QM806. The second glycoprotein, a mannan-protein complex, after immobilization, has been used in the purification of an alpha-D-mannosidase from jack-bean meal.

The effect of thiols on Saccharomyces fragilis

Treatment of cell suspensions of Saccharomyces fragilis with 0.01 M beta-mercaptoethanol or dithiothreitol released a variety of substances of high and low molecular weight. Twenty-two high-molecular-weight glycoproteins were separated by a combination of chromatography on DEAE cellulose and polyacrylamide gel electrophoresis in presence of sodium dodecylsulphate. The carbohydrate components consisted of at least 95% mannose and the protein components had threonine and serine as the major amino acids. Only very small amounts of phosphorus were associated with the high-molecular-weight components. The low-molecular-weight substances werr probably released from the internal cell pool and uracil and hypoxanthine were identified as components of this fraction. It is suggested that in addition to breaking disulphide bridges in the cell wall the thiols may also render the plasmalemma permeable to certain low-molecular-weight substances. Such effects are not lethal since the yeast can be trained to grow in presence of 0.01 M mercaptoethanol.