Structures of wall heterogalactomannans isolated from three genera of entomopathogenic fungi

Biotech Application of Exopolysaccharides from Curvularia brachyspora: Optimization of Production, Structural Characterization, and Biological Activity

C. brachyspora, a widespread dematiaceous fungus, was evaluated in this study to optimize the production of exopolysaccharides (CB-EPS). Optimization was performed using response surface methodology, and the best production yielded 75.05% of total sugar at pH 7.4, with 0.1% urea, after 197 h. The obtained CB-EPS showed typical signals of polysaccharides, which was confirmed by FT-IR and NMR. The HPSEC analysis indicated a polydisperse polymer, showing a non-uniform peak, with an average molar mass (M_w) of 24,470 g/mol. The major monosaccharide was glucose (63.9 Mol%), followed by mannose (19.7 Mol%), and galactose (16.4 Mol%). Methylation analysis encountered derivatives that indicated the presence of a β-d-glucan and a highly branched glucogalactomannan. CB-EPS was tested on murine macrophages to verify its immunoactivity, and the treated cells were able to produce TNF-α, IL-6, and IL-10. However, the cells did not produce superoxide anions or nitric oxide nor stimulated phagocytosis. The results demonstrated an indirect antimicrobial activity of macrophages by stimulating cytokines, showing another biotech applicability for the exopolysaccharides produced by C. brachyspora.

A review of NMR analysis in polysaccharide structure and conformation: Progress, challenge and perspective

Nuclear magnetic resonance (NMR) has been widely used as an analytical chemistry technique to investigate the molecular structure and conformation of polysaccharides. Combined with 1D spectra, chemical shifts and coupling constants in both homo- and heteronuclear 2D NMR spectra are able to infer the linkage and sequence of sugar residues. Besides, NMR has also been applied in conformation, quantitative analysis, cell wall in situ, degradation, polysaccharide mixture interaction analysis, as well as carbohydrates impurities profiling. This review summarizes the principle and development of NMR in polysaccharides analysis, and provides NMR spectra data collections of some common polysaccharides. It will help to promote the application of NMR in complex polysaccharides of biochemical interest, and provide valuable information on commercial polysaccharide products.

Effects of supplementation of sea buckthorn press cake on mycelium growth and polysaccharides of Inonotus obliquus in submerged cultivation

AIMS

Investigation of the influence of cultivation time and sea buckthorn press cake (Hippophaë rhamnoides) dosage on mycelium yield of Inonotus obliquus in submerged cultivation and on the yield, monomer composition, and macromolecular properties of the exopolysaccharides (EPS) from culture media and intracellular polysaccharides (IPS) extracted from mycelia.

METHODS AND RESULTS

Supplementation at 5 g l^-1 combined with cultivation time of 250 h granted highest yield increase in mycelia (by 122%). The supplementation reduced extraction yield and decreased the molecular weight of the main IPS population. The supplementation increased production and molecular weight of EPS. The relative content of arabinose and rhamnose in EPS positively correlated with dosage of the press cake. The press cake supplementation increased the content of galacturonic acid in IPS, but not in EPS.

CONCLUSION

Sea buckthorn press cake is a food industry fibrous side stream with high oil content. It increases the cultivation yield of Inonotus obliquus mycelium and influences the produced polysaccharides.

SIGNIFICANCE AND IMPACT OF THE STUDY

Mycelium is a resource of bioactive polysaccharides, attracting the interest of nutraceutical companies. Sea buckthorn press cake is a promising supplement for increasing mycelium production. The utilization of this agricultural side stream would therefore favour circular economy.

Chlorella vulgaris α-L-arabino-α-L-rhamno-α,β-D-galactan structure and mechanisms of its anti-inflammatory and anti-remodelling effects

Microalgal exopolysaccharides (EPSs) are given great attention due to their potential biotechnology applications. Purified C. vulgaris EPS was subjected to compositional and sugar linkage analyses, and partial acid hydrolysis. Hydrolysate separation by gel chromatography afforded oligosaccharide fractions. Both, EPS and oligomers were studied by NMR spectroscopy. Data suggest very complex highly branched α-L-arabino-α-L-rhamno-α,β-D-galactan structure. Backbone repeating unit is formed by →2)-α-L-Rha (1 → 3)-α-L-Rha(1 → sequence, highly branched by long 1,6-linked α-D-Galp side chains, further branched at C2, C3 or C4 by α-L-Araf, α-D-Galf and β-D-Galf residues. α-L-Araf form longer 1,2-linked chains branched at C3, C4 or C5. Galf residues are localized as terminal units predominantly in the β configuration, while α-D-Galp and α-L-Araf may be partially O-methylated. Ex vivo biological assays showed increased interleukin-12 (IL-12) and interferon-gamma (INF-γ) levels corresponding to transforming growth factor beta (TGF-β) decrease in guinea pig model experimental asthma. These facts point to the anti-remodelling effect of Chlorella EPS and suggest its possible application in the treatment of asthma and chronic obstructive pulmonary disorder.

Exploiting xylan as sugar donor for the synthesis of an antiproliferative xyloside using an enzyme cascade

BACKGROUND

Currently, industrial societies are seeking for green alternatives to conventional chemical synthesis. This demand has merged with the efforts to convert lignocellulosic biomass into value-added products. In this context, xylan, as one of main components of lignocellulose, has emerged as a raw material with high potential for advancing towards a sustainable economy.

RESULTS

In this study, the recombinant endoxylanase rXynM from the ascomycete Talaromyces amestolkiae has been heterologously expressed in Pichia pastoris and used as one of the catalysts of an enzyme cascade developed to synthesize the antiproliferative 2-(6-hydroxynaphthyl) β-D-xylopyranoside, by transglycosylation of 2,6-dihydroxynaphthalene. The approach combines the use of two fungal xylanolytic enzymes, rXynM and the β-xylosidase rBxTW1 from the same fungus, with the cost-effective substrate xylan. The reaction conditions for the cascade were optimized by a Central Composite Design. Maximal productions of 0.59 and 0.38 g/L were reached using beechwood xylan and birchwood xylan, respectively. For comparison, xylans from other sources were tested in the same reaction, suggesting that a specific optimization is required for each xylan variety. The results obtained using this enzyme cascade and xylan were similar or better to those previously reported for a single catalyst and xylobiose, an expensive sugar donor.

CONCLUSIONS

Beechwood and birchwood xylan, two polysaccharides easily available from biomass, were used in a novel enzyme cascade to synthetize an antiproliferative agent. The approach represents a green alternative to the conventional chemical synthesis of 2-(6-hydroxynaphthyl) β-D-xylopyranoside using a cost-effective substrate. The work highlights the role of xylan as a raw material for producing value-added products and the potential of fungal xylanolytic enzymes in the biomass conversion.

Silencing barley cystatins HvCPI-2 and HvCPI-4 specifically modifies leaf responses to drought stress

Protein breakdown and mobilization are some of the major metabolic features associated with abiotic stresses, essential for nutrient recycling and plant survival. Genetic manipulation of protease and/or protease inhibitors may contribute to modulate proteolytic processes and plant responses. The expression analysis of the whole cystatin family, inhibitors of C1A cysteine proteases, after water deprivation in barley leaves highlighted the involvement of Icy-2 and Icy-4 cystatin genes. Artificial microRNA lines independently silencing the two drought-induced cystatins were generated to assess their function in planta. Phenotype alterations at the final stages of the plant life cycle are represented by the stay-green phenotype of silenced cystatin 2 lines. Besides, the enhanced tolerance to drought and differential responses to water deprivation at the initial growing stages are observed. The mutual compensating expression of Icy-2 and Icy-4 genes in the silencing lines pointed to their cooperative role. Proteolytic patterns by silencing these cystatins were concomitant with modifications in the expression of potential target proteases, in particular, HvPap-1, HvPap-12, and HvPap-16 C1A proteases. Metabolomics analysis lines also revealed specific modifications in the accumulation of several metabolites. These findings support the use of plants with altered proteolytic regulation in crop improvement in the face of climate change.

cpsA regulates mycotoxin production, morphogenesis and cell wall biosynthesis in the fungus Aspergillus nidulans

The model fungus Aspergillus nidulans synthesizes numerous secondary metabolites, including sterigmatocystin (ST). The production of this toxin is positively controlled by the global regulator veA. In the absence of veA (ΔveA), ST biosynthesis is blocked. Previously, we performed random mutagenesis in a ΔveA strain and identified revertant mutants able to synthesize ST, among them RM1. Complementation of RM1 with a genomic library revealed that the mutation occurred in a gene designated as cpsA. While in the ΔveA genetic background cpsA deletion restores ST production, in a veA wild-type background absence of cpsA reduces and delays ST biosynthesis decreasing the expression of ST genes. Furthermore, cpsA is also necessary for the production of other secondary metabolites, including penicillin, affecting the expression of PN genes. In addition, cpsA is necessary for normal asexual and sexual development. Chemical and microscopy analyses revealed that CpsA is found in cytoplasmic vesicles and it is required for normal cell wall composition and integrity, affecting adhesion capacity and oxidative stress sensitivity. The conservation of cpsA in Ascomycetes suggests that cpsA homologs might have similar roles in other fungal species.

Enzymatic fine-tuning for 2-(6-hydroxynaphthyl) β-D-xylopyranoside synthesis catalyzed by the recombinant β-xylosidase BxTW1 from Talaromyces amestolkiae

Background

Glycosides are compounds displaying crucial biological roles and plenty of applications. Traditionally, these molecules have been chemically obtained, but its efficient production is limited by the lack of regio- and stereo-selectivity of the chemical synthesis. As an interesting alternative, glycosidases are able to catalyze the formation of glycosides in a process considered green and highly selective. In this study, we report the expression and characterization of a fungal β-xylosidase in Pichia pastoris. The transglycosylation potential of the enzyme was evaluated and its applicability in the synthesis of a selective anti-proliferative compound demonstrated.

Results

The β-xylosidase BxTW1 from the ascomycete fungus Talaromyces amestolkiae was cloned and expressed in Pichia pastoris GS115. The yeast secreted 8 U/mL of β-xylosidase that was purified by a single step of cation-exchange chromatography. rBxTW1 in its active form is an N-glycosylated dimer of about 200 kDa. The enzyme was biochemically characterized displaying a K_m and k_cat against p-nitrophenyl-β-d-xylopyranoside of 0.20 mM and 69.3 s⁻¹ respectively, and its maximal activity was achieved at pH 3 and 60 °C. The glycan component of rBxTW1 was also analyzed in order to interpret the observed loss of stability and maximum velocity when compared with the native enzyme. A rapid screening of aglycone specificity was performed, revealing a remarkable high number of potential transxylosylation acceptors for rBxTW1. Based on this analysis, the enzyme was successfully tested in the synthesis of 2-(6-hydroxynaphthyl) β-d-xylopyranoside, a well-known selective anti-proliferative compound, enzymatically obtained for the first time. The application of response surface methodology, following a Box-Behnken design, enhanced this production by eightfold, fitting the reaction conditions into a multiparametric model. The naphthyl derivative was purified and its identity confirmed by NMR.

Conclusions

A β-xylosidase from T. amestolkiae was produced in P. pastoris and purified. The final yields were much higher than those attained for the native protein, although some loss of stability and maximum velocity was observed. rBxTW1 displayed remarkable acceptor versatility in transxylosylation, catalyzing the synthesis of a selective antiproliferative compound, 2-(6-hydroxynaphthyl) β-d-xylopyranoside. These results evidence the interest of rBxTW1 for transxylosylation of relevant products with biotechnological interest.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0568-6) contains supplementary material, which is available to authorized users.

Comparative proteomic analyses reveal that Gnt2-mediated N-glycosylation affects cell wall glycans and protein content in Fusarium oxysporum

Protein N-glycosylation is a ubiquitous post-translational modification that contributes to appropriate protein folding, stability, functionality and localization. N-glycosylation has been identified as an important process for morphogenesis and virulence in several fungal pathogens including Fusarium oxysporum. Here we conducted comparative chemical and proteome-based analyses to better understand the physiological changes associated with protein hypo-N-glycosylation in F. oxysporum N-glycosyltransferase Gnt2-deficient mutant. The results suggest that lack of functional Gnt2 alters the size of galactofuranose chains in cell wall glycans, resulting in polysaccharides with a broad range of polymerization degrees and differential protein glycosylation patterns. Functional Gnt2 is necessary for normal conidium size and morphology and wild-type hyphal fusion rates. Hypo-N-glycosylation in ∆gnt2 mutant results in enhanced oxidative stress resistance and reduced levels of proteins involved in cell wall organization, biogenesis and remodelling. Deletion of gnt2 gene led to accumulation of trafficking vesicles at hyphal tips, reduced secretion of extracellular proteins related to detoxification of antifungal compounds and degradation of plant cell walls, and lowered extracellular polygalacturonase activity. Altogether, the results confirm that Gnt2-mediated N-glycosylation plays a crucial role in morphogenesis and virulence, and demonstrate that Gnt2 is essential for protein function, transport and relative abundance in F. oxysporum.

Enzymatic degradation of Elephant grass (Pennisetum purpureum) stems: influence of the pith and bark in the total hydrolysis

The internal pith of a high energy plant, Elephant grass (EG), was more extensively degraded (>50% dry matter) compared to the outer cortex (31%) or the whole stem (35%) by an enzyme preparation from Humicola insolens, Ultraflo. Reducing sugars and acetic acid release from the pith was also higher compared to the cortex. Supplementation of Ultraflo with a type-C feruloyl esterase increased the level of deacetylation but also led to reduced solubilisation. The addition of 20% dimethyl sulfoxide (DMSO) as a co-solvent also reduced the solubility of EG by Ultraflo, although acetic acid release was increased, complimenting previous results found on model substrates. The presence of DMSO was also shown to have a protective effect on xylanase activity but not acetyl esterase activity in Ultraflo. Xylan in the biomass was preferentially solubilised by DMSO, while Ultraflo removed more glucose than xylose.

Jasmonate-dependent modifications of the pectin matrix during potato development function as a defense mechanism targeted by Dickeya dadantii virulence factors

The plant cell wall constitutes an essential protection barrier against pathogen attack. In addition, cell-wall disruption leads to accumulation of jasmonates (JAs), which are key signaling molecules for activation of plant inducible defense responses. However, whether JAs in return modulate the cell-wall composition to reinforce this defensive barrier remains unknown. The enzyme 13-allene oxide synthase (13-AOS) catalyzes the first committed step towards biosynthesis of JAs. In potato (Solanum tuberosum), there are two putative St13-AOS genes, which we show here to be differentially induced upon wounding. We also determine that both genes complement an Arabidopsis aos null mutant, indicating that they encode functional 13-AOS enzymes. Indeed, transgenic potato plants lacking both St13-AOS genes (CoAOS1/2 lines) exhibited a significant reduction of JAs, a concomitant decrease in wound-responsive gene activation, and an increased severity of soft rot disease symptoms caused by Dickeya dadantii. Intriguingly, a hypovirulent D. dadantii pel strain lacking the five major pectate lyases, which causes limited tissue maceration on wild-type plants, regained infectivity in CoAOS1/2 plants. In line with this, we found differences in pectin methyl esterase activity and cell-wall pectin composition between wild-type and CoAOS1/2 plants. Importantly, wild-type plants had pectins with a lower degree of methyl esterification, which are the substrates of the pectate lyases mutated in the pel strain. These results suggest that, during development of potato plants, JAs mediate modification of the pectin matrix to form a defensive barrier that is counteracted by pectinolytic virulence factors from D. dadantii.

Fungal exopolysaccharide: production, composition and applications

Fungal exopolysaccharides (EPSs) have been recognized as high value biomacromolecules for the last two decades. These products, including pullulan, scleroglucan, and botryosphaeran, have several applications in industries, pharmaceuticals, medicine, foods etc. Although fungal EPSs are highly relevant, to date information concerning fungal biosynthesis is scarce and an extensive search for new fugal species that can produce novel EPSs is still needed. In most cases, the molecular weight variations and sugar compositions of fungal EPSs are dependent to culture medium composition and different physical conditions provided during fermentation. An inclusive and illustrative review on fungal EPS is presented here. The general outline of the present work includes fungal EPS production, their compositions and applications. An emphasis is also given to listing out different fungal strains that can produce EPSs.