Scleroglucan

One-step production of functional branched oligoglucosides with coupled fermentation of Pichia pastoris GS115 and Sclerotium rolfsii WSH-G01

Endo-β-1,3-glucanase with high specific activity is a prerequisite for enzymatic preparation of valuable β-oligoglucosides. Heterologous expression in Pichia pastoris GS115 with error-prone PCR technology was implemented, and the mutant strain 7 N12 was obtained. The mutant endo-β-1,3-glucanase showed efficient specific activities for degrading curdlan (366 U mg^-1) and scleroglucan (274.5 U mg^-1). Thereafter, one-step production of functional branched oligoglucosides was established with coupled fermentation of Pichia pastoris and Sclerotium rolfsii. During the fermentation process, the endo-β-1,3-glucanase secreted by Pichia pastoris GS115 can efficiently hydrolyse scleroglucan metabolized by Sclerotium rolfsii WSH-G01. The maximum yields of β-oligoglucosides in the shake flasks and 7-L bioreactor reached 1.73 g L^-1 and 12.71 g L^-1, respectively, with polymerization degrees of 2-17. The successful implementation of heterologous expression with error-prone PCR and the coupled fermentation simplified the multi-step enzymatic β-oligoglucoside preparation procedures, which makes it a potential strategy for industrial production of functional oligosaccharides.

Triple-helix polysaccharides: Formation mechanisms and analytical methods

Triple helix conformation of polysaccharides is generally believed to be associated with their biological activities. However, the formation mechanisms and analytical methods for the triple helix polysaccharides, to our best knowledge, have not been systematically investigated. This article reviews specifically the literature on the formation and characterization of triple-helix polysaccharides. The formation mechanisms and related structural-conformation-bioactivity relationships are discussed; various analytical methods for characterizing triple-helix polysaccharides are summarized. This review devotes to a better understanding of the formation of polysaccharides based triple-helix structure and related analytical methods. These could provide some insights and inspirations for their applications in both food and pharmaceutical industries.

Progress in rigid polysaccharide-based nanocomposites with therapeutic functions

Nanocomposites engineered by incorporating versatile nanoparticles into different bioactive β-glucan matrices display effective therapeutic functions.

Microbial production of scleroglucan and downstream processing

Synthetic petroleum-based polymers and natural plant polymers have the disadvantage of restricted sources, in addition to the non-biodegradability of the former ones. In contrast, eco-sustainable microbial polysaccharides, of low-cost and standardized production, represent an alternative to address this situation. With a strong global market, they attracted worldwide attention because of their novel and unique physico-chemical properties as well as varied industrial applications, and many of them are promptly becoming economically competitive. Scleroglucan, a β-1,3-β-1,6-glucan secreted by Sclerotium fungi, exhibits high potential for commercialization and may show different branching frequency, side-chain length, and/or molecular weight depending on the producing strain or culture conditions. Water-solubility, viscosifying ability and wide stability over temperature, pH and salinity make scleroglucan useful for different biotechnological (enhanced oil recovery, food additives, drug delivery, cosmetic and pharmaceutical products, biocompatible materials, etc.), and biomedical (immunoceutical, antitumor, etc.) applications. It can be copiously produced at bioreactor scale under standardized conditions, where a high exopolysaccharide concentration normally governs the process optimization. Operative and nutritional conditions, as well as the incidence of scleroglucan downstream processing will be discussed in this chapter. The relevance of using standardized inocula from selected strains and experiences concerning the intricate scleroglucan scaling-up will be also herein outlined.

Isolation and characterization of extracellular polysaccharide Thelebolan produced by a newly isolated psychrophilic Antarctic fungus Thelebolus

The present investigation is on a newly isolated psychrophilic Antarctic filamentous Ascomycetous fungus that has been identified as Thelebolus sp. and given the designation of Thelebolus sp. IITKGP-BT12. The culture was primarily identified through morphological studies, and was further confirmed by 18S rRNA sequencing (GenBank Accession No. KC191572), which revealed its close relatedness with Thelebolus microsporus. The exopolysaccharide (EPS) produced (1.94 g L(-1)) by the fungus was isolated, purified and characterized as glucan having an average molecular mass of 5×10(5)Da. The structure of EPS was determined by gas chromatography with tandem mass spectrometry (GC-MS/MS), Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) studies ((1)H, (13)C and HSQC). NMR analysis indicated the presence of (1→3)-linked β-d-glucan backbone with (1→6)-linked branches of β-d-glucopyranosyl units. Antiproliferative activity of EPS was demonstrated in B16-F0 cells, with IC50 of 275.42 μg m L(-1). Flow cytometry analysis and DNA fragmentation studies revealed that the cytotoxic action of the EPS mediated apoptosis in cancer cells. This is the first ever report on bioactive EPS thelebolan from Thelebolus sp.

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.

Deoiledjatropha seed cake is a useful nutrient for pullulan production

Background

Ever increasing demand for fossil fuels is a major factor for rapid depletion of these non-renewable energy resources, which has enhanced the interest of finding out alternative sources of energy. In recent years jatropha seed oil has been used extensively for production of bio-diesel and has shown significant potential to replace petroleum fuels at least partially. De-oiled jatropha seed cake (DOJSC) which comprises of approximately 55 to 65% of the biomass is a byproduct of bio-diesel industry. DOJSC contains toxic components like phorbol esters which restricts its utilization as animal feed. Thus along with the enhancement of biodiesel production from jatropha, there is an associated problem of handling this toxic byproduct. Utilization of DOJSC as a feed stock for production of biochemicals may be an attractive solution to the problem.

Pullulan is an industrially important polysaccharide with several potential applications in food, pharmaceuticals and cosmetic industries. However, the major bottleneck for commercial utilization of pullulan is its high cost. A cost effective process for pullulan production may be developed using DOJSC as sole nutrient source which will in turn also help in utilization of the byproduct of bio-diesel industry.

Results

In the present study, DOJSC has been used as a nutrient for production of pullulan, in place of conventional nutrients like yeast extract and peptone. Process optimization was done in shake flasks, and under optimized conditions (8% DOJSC, 15% dextrose, 28°C temperature, 200 rpm, 5% inoculum, 6.0 pH) 83.98 g/L pullulan was obtained. The process was further validated in a 5 L laboratory scale fermenter.

Conclusion

This is the first report of using DOJSC as nutrient for production of an exopolysaccharide. Successful use of DOJSC as nutrient will help in finding significant application of this toxic byproduct of biodiesel industry. This in turn also have a significant impact on cost reduction and may lead to development of a cost effective green technology for pullulan production.

Transcriptome sequencing and comparative transcriptome analysis of the scleroglucan producer Sclerotium rolfsii

BACKGROUND

The plant pathogenic basidiomycete Sclerotium rolfsii produces the industrially exploited exopolysaccharide scleroglucan, a polymer that consists of (1 --> 3)-beta-linked glucose with a (1 --> 6)-beta-glycosyl branch on every third unit. Although the physicochemical properties of scleroglucan are well understood, almost nothing is known about the genetics of scleroglucan biosynthesis. Similarly, the biosynthetic pathway of oxalate, the main by-product during scleroglucan production, has not been elucidated yet. In order to provide a basis for genetic and metabolic engineering approaches, we studied scleroglucan and oxalate biosynthesis in S. rolfsii using different transcriptomic approaches.

RESULTS

Two S. rolfsii transcriptomes obtained from scleroglucan-producing and scleroglucan-nonproducing conditions were pooled and sequenced using the 454 pyrosequencing technique yielding approximately 350,000 reads. These could be assembled into 21,937 contigs and 171,833 singletons, for which 6,951 had significant matches in public protein data bases. Sequence data were used to obtain first insights into the genomics of scleroglucan and oxalate production and to predict putative proteins involved in the synthesis of both metabolites. Using comparative transcriptomics, namely Agilent microarray hybridization and suppression subtractive hybridization, we identified approximately 800 unigenes which are differently expressed under scleroglucan-producing and non-producing conditions. From these, candidate genes were identified which could represent potential leads for targeted modification of the S. rolfsii metabolism for increased scleroglucan yields.

CONCLUSIONS

The results presented in this paper provide for the first time genomic and transcriptomic data about S. rolfsii and demonstrate the power and usefulness of combined transcriptome sequencing and comparative microarray analysis. The data obtained allowed us to predict the biosynthetic pathways of scleroglucan and oxalate synthesis and to identify important genes putatively involved in determining scleroglucan yields. Moreover, our data establish the first sequence database for S. rolfsii, which allows research into other biological processes of S. rolfsii, such as host-pathogen interaction.

Sclerotium rolfsii scleroglucan: The promising behavior of a natural polysaccharide as a drug delivery vehicle, suspension stabilizer and emulsifier

Gel matrices of scleroglucans from Sclerotium rolfsii ATCC 201126 (EPS I and EPS II, from 48-h and 72-h fermentations, respectively) were evaluated on their release kinetics of theophylline (Th). Equivalent polymer (2%, w/w) and Th (0.2%, w/w) concentrations showed almost coincident drug release patterns, independently of polymer molecular weight or the microstructural properties of gel matrices. Dynamic rheological studies of scleroglucan hydrogel structures (storage, G', and loss, G'', moduli) indicated a solid-like behavior. Differences on pore size dimensions (EPS I=20 microm and EPS II=7 microm) were in accordance to the differences in G' (EPS I=113 Pa and EPS II=161 Pa), a fact likely related to variations in the cross-linking density of polymer networks. Compared to already known biopolymers, EPS I and EPS II at 0.5 g/L showed a good dispersing ability against particulate suspensions of activated charcoal, bentonite, CaCO(3), celite and quartz powder. Emulsifying ability of both EPSs at 2g/L was high (E=56-60%) when tested with kerosene, moderate ( approximately 30%) with hexadecane, and negligible in the presence of olive oil-in-water emulsions.

Use of complex media for the production of scleroglucan by Sclerotium rolfsii MTCC 2156

Submerged fermentation was carried out for the production of scleroglucan by Sclerotium rolfsii MTCC 2156 using complex media, such as coconut water, sugarcane molasses and sugarcane juice at 28+/-2 degrees C and 180 rpm for 72 h. Sugarcane juice gave maximum scleroglucan production of 23.87 g/l as compared to 12.58 and 18.45 g/l with coconut water and sugarcane molasses, respectively. Utilization of these substrates would be ecologically sound and economically advantageous.

Production of ?-glucan and related glucan-hydrolases by Botryosphaeria rhodina

AIMS

Characterization of beta-glucan production from Botryosphaeria rhodina DABAC-P82 by detecting simultaneously glucan-hydrolytic enzymes and their localization, culture medium rheology and oxygen transfer.

METHODS AND RESULTS

Mycelium growth, beta-glucan production, substrate consumption and glucan-hydrolytic enzymes were monitored both in shaken flasks and in a 3-l stirred-tank bioreactor. Glucan production (19.7 and 15.2 g l(-1), in flask and bioreactor, respectively) was accompanied by extra-cellular and cell-bound beta-glucanase and beta-glucosidase activities. In the bioreactor scale, in the time interval of 0-78 h the apparent viscosity of the culture broth exhibited a general increase; thereafter, it began to reduce, probably because of the above glucan-hydrolytic activities. Moreover, the culture media collected after 45 h behaved as solid-like materials at shear rates smaller than 0.001 s(-1), as pseudo-plastic liquids in the middle shear rate range and as Newtonian ones at shear rates greater than 1000 s(-1).

CONCLUSION

The greatest beta-glucan accumulation in the bioreactor was found to be associated with nitrogen and dissolved oxygen concentrations smaller than 0.15 g l(-1) and 25%, respectively, and with the peak points of the glucan-degrading enzymes.

SIGNIFICANCE AND IMPACT OF THE STUDY

A careful analysis of the critical factors (such as, culture broth rheology, oxygen mass transfer and glucan-hydrolytic enzymes) limiting the beta-glucan production by B. rhodina is a prerequisite to maximize beta-glucan yield and production, as well as to define the process flow sheet capable of maximizing biopolymer recovery, solvent re-utilization and glucose consumption.

Enhanced production of scleroglucan by Sclerotium rolfsii MTCC 2156 by use of metabolic precursors

The aim of this work was to study the effect of addition of different amino acids and sugar nucleotides as metabolic precursors on the production of scleroglucan. A maximum yield of 20.00 g/l and 22.32 g/l was obtained with optimized media supplemented with L-lysine (1.1 mM) and uridine mono-phosphate (UMP), respectively as compared to 16.52 g/l scleroglucan achieved with the control in the absence of metabolic precursors.

Small angle x-ray scattering study of local structure and collapse transition of (1,3)-β-D-glucan-chitosan gels

Scleroglucan is a (1,3)-beta-D-glucan polysaccharide produced by the fungus Sclerotium. Dissolved in water at room temperature it adopts a linear, rigid, triple helical structure. Gelation of scleroglucan can be obtained by Schiff-base formation between partly periodate oxidized scleroglucan and the primary amine groups of chitosan. The scleraldehyde-chitosan gels exhibit a collapse transition when exposed to volume fractions of isopropanol, Wp, larger than 65%. The aim of the present study is to provide structural information concerning the local polymer distribution and the collapse transition in (1,3)-beta-D-glucan-chitosan gels. Small angle x-ray scattering was used to investigate solutions and gels of scleroglucan in water, as well as in an aqueous mixture containing 65% isopropanol. The results reveal that in aqueous solution, the polysaccharide scleroglucan chains have an approximately cylindrical cross section of external diameter close to 17 A. The gels display the same local structure, but form clusters on a longer distance scale. For the collapsed gels in the water-isopropanol mixture, partial phase separation occurs in which ordered domains of approximate size of 110 A develop. This study indicates that local ordering in liquid-crystalline-type domains is a possible molecular mechanism contributing to the collapse of gels composed of semiflexible polymers. The triple helical structure of the molecule appears not to be conserved in the majority phase in this solvent, but it is conserved in the liquid crystalline domains.

Beta-glucan production by Botryosphaeria rhodina in different bench-top bioreactors

AIMS

Evaluation of the technical feasibility of transferring beta-glucan production by Botryosphaeria rhodina DABAC-P82 from shaken flasks to bench-top bioreactors.

METHODS AND RESULTS

Three different bioreactors were used: 3 l stirred tank reactor (STR-1) equipped with two different six-blade turbines; STR as above but equipped with a three-blade marine propeller plus draft-tube (STR-2); 2 l air-lift column reactor (ALR) equipped with an external loop. STR-1, tested at three different stirrer speeds (300, 500 and 700 rev min(-1)) appeared to be less suitable for beta-glucan production by the fungus, being maximum production (19.4 g l(-1)), productivity (0.42 g l(-1) h(-1)) and yield (0.48 g g(-1) of glucose consumed) markedly lower than those obtained in shaken culture (29.7 g l(-1), 1.23 g l(-1) h(-1) and 0.61 g g(-1), respectively). Better performances were obtained with both STR-2 and ALR. With the latter, in particular, the increase of production was accompanied by reduced fermentation time (25.7 g l(-1) after only 22 h); productivity and yield were highest (1.17 g l(-1) h(-1) and 0.62 g g(-1) of glucose consumed, respectively).

CONCLUSION

Using an air-lift reactor with external loop, the scaling up from shaken flasks to bench-top bioreactor of the beta-glucan production by B. rhodina DABAC-P82 is technically feasible.

SIGNIFICANCE AND IMPACT OF THE STUDY

Although culture conditions are still to be optimized, the results obtained using the ARL are highly promising.

Production and structural characterization of the exopolysaccharide of the Antarctic fungus Phoma herbarum CCFEE 5080

The filamentous fungus Phoma herbarum CCFEE 5080 isolated from continental Antarctica soil was tested for exopolysaccharide (EPS) production. The fungus grew and produced EPS (up to 13.6 g/l) on a variety of carbon sources among which sorbitol was best, particularly at the concentration of 60 g/l. EPS production was maximum when the nitrogen source was NaNO3 (3 g/l) and the incubation temperature was 28 degrees C. The polysaccharide was purified by repeated precipitation in ethanol and gel filtration and characterized as a homopolymer of glucose having a molecular weight of 7.412 x 10(6); structural analysis indicated the presence of beta-1,3 and beta-1,6 linkages only. After repeated freezing and thawing of the fungal biomass in the presence of EPS, the mycelial growth was much higher than that observed after freezing in the absence of EPS and the difference increased with the number of freeze-thaw cycles. It is hypothesized that the adaptation of P. herbarum CCFEE 5080 to the Antarctic soil microclimatic conditions, characterized by low temperature, high thermal fluctuations and repeated freeze-thaw cycles, might be related to the EPS production ability.

Exopolysaccharide production from Sclerotium glucanicum NRRL 3006 and Botryosphaeria rhodina DABAC-P82 on raw and hydrolysed starchy materials

AIMS

Evaluation of fermentative usage of raw starchy materials for exopolysaccharide (EPS) production by Sclerotium glucanicum NRRL 3006 and Botryosphaeria rhodina DABAC-P82.

METHODS AND RESULTS

Non-hydrolysed corn starch, soft wheat flour, potato flour, cassava flour, sweet and industrial potato flours, and corn starch hydrolysed to different dextrose equivalent (DE) were tested in shaken culture for EPS production. Both fungal strains produced EPS on all tested materials but the production was maximum on hydrolysed corn starch (30.5 and 19.8 g l(-1) by B. rhodina and S. glucanicum on corn starch at 100 and 62 DE, respectively).

CONCLUSIONS

Raw starchy materials as such and, in particular, partially or totally hydrolysed corn starch could be used profitably for EPS production by S. glucanicum and B. rhodina.

SIGNIFICANCE AND IMPACT OF THE STUDY

The excellent EPS production, productivity and yield of B. rhodina DABAC-P82 when grown on 60 g l(-1) of totally hydrolysed corn starch.

A (1-->3)-beta-D-linked heptasaccharide is the unit ligand for glucan pattern recognition receptors on human monocytes

Glucans are fungal cell wall polysaccharides which stimulate innate immune responses. We determined the minimum unit ligand that would bind to glucan receptors on human U937 cells using laminarin-derived pentaose, hexaose, and heptaose glucan polymers. When U937 membranes were pretreated with the oligosaccharides and passed over a glucan surface, only the heptasaccharide inhibited the interaction of glucan with membrane receptors at a K(d) of 31 microM (95% CI 20-48 microM) and 100% inhibition. However, the glucan heptasaccharide did not stimulate U937 monocyte NFkappaB signaling, nor did it increase survival in a murine model of polymicrobial sepsis. Laminarin, a larger and more complex glucan polymer (M(w) = 7700 g/mol), only partially inhibited binding (61 +/- 4%) at a K(d) of 2.6 microM (99% CI 1.7-4.2 microM) with characteristics of a single binding site. These results indicate that a heptasaccharide is the smallest unit ligand recognized by macrophage glucan receptors. The data also indicate the presence of at least two glucan-binding sites on U937 cells and that the binding sites on human monocyte/macrophages can discriminate between glucan polymers. The heptasaccharide and laminarin were receptor antagonists, but they were not receptor agonists with respect to activation of NFkappaB-dependent signaling pathways or protection against experimental sepsis.

Gellan gum

For decades microbial exopolysaccharides have been invaluable ingredients in the food industry, as well as having many attractive pharmaceutical and chemical applications. Gellan gum is a comparatively new gum elaborated by the Gram-negative bacterium Sphingomonas paucimobilis. Although its physico-chemical properties have been well characterized, the ecology and physiology of Sphingomonas, and the factors influencing the fermentation process for production of this gum have received much less attention. This review focuses on the metabolism and the enzymic activity of this bacterium, as well as the factors that influence gellan production, including process temperature, pH, stirring rate, oxygen transfer, and composition of the production medium. Potential strategies for improving the production process are discussed in the context of processes for the production of other microbial biopolymers, particularly exopolysaccharides. In addition, the importance and potential utility of gellan lyases in modification of gellan and in other applications is critically evaluated.