Biocatalytic Synthesis of Fungal β-Glucans

How do the carbon and nitrogen sources affect the synthesis of β-(1,3/1,6)-glucan, its structure and the susceptibility of Candida utilis yeast cells to immunolabelling with β-(1,3)-glucan monoclonal antibodies?

BACKGROUND

The need to limit antibiotic therapy due to the spreading resistance of pathogenic microorganisms to these medicinal substances stimulates research on new therapeutic agents, including the treatment and prevention of animal diseases. This is one of the goals of the European Green Deal and the Farm-To-Fork strategy. Yeast biomass with an appropriate composition and exposure of cell wall polysaccharides could constitute a functional feed additive in precision animal nutrition, naturally stimulating the immune system to fight infections.

RESULTS

The results of the research carried out in this study showed that the composition of Candida utilis ATCC 9950 yeast biomass differed depending on growth medium, considering especially the content of β-(1,3/1,6)-glucan, α-glucan, and trehalose. The highest β-(1,3/1,6)-glucan content was observed after cultivation in deproteinated potato juice water (DPJW) as a nitrogen source and glycerol as a carbon source. Isolation of the polysaccharide from yeast biomass confirmed the highest yield of β-(1,3/1,6)-glucan after cultivation in indicated medium. The differences in the susceptibility of β-(1,3)-glucan localized in cells to interaction with specific β-(1,3)-glucan antibody was noted depending on the culture conditions. The polymer in cells from the DPJW supplemented with glycerol and galactose were labelled with monoclonal antibodies with highest intensity, interestingly being less susceptible to such an interaction after cell multiplication in medium with glycerol as carbon source and yeast extract plus peptone as a nitrogen source.

CONCLUSIONS

Obtained results confirmed differences in the structure of the β-(1,3/1,6)-glucan polymers considering side-chain length and branching frequency, as well as in quantity of β-(1,3)- and β-(1,6)-chains, however, no visible relationship was observed between the structural characteristics of the isolated polymers and its susceptibility to immunolabeling in whole cells. Presumably, other outer surface components and molecules can mask, shield, protect, or hide epitopes from antibodies. β-(1,3)-Glucan was more intensely recognized by monoclonal antibody in cells with lower trehalose and glycogen content. This suggests the need to cultivate yeast biomass under appropriate conditions to fulfil possible therapeutic functions. However, our in vitro findings should be confirmed in further studies using tissue or animal models.

Vegan shrimp alternative made with pink oyster and lion's mane mushrooms: Nutritional profiles, presence of conjugated phenolic acids, and prototyping

The increasing demand for seafood is responsible for many environmental impacts, especially caused by aquaculture. Shrimp accounts for a substantial part of seafood production and therefore also for negative effects associated with it. This work aimed to develop a mushroom-based shrimp analogue with a texture similar to shrimp using the fruiting bodies of pink oyster mushroom (Pleurotus djamor) and lion's mane (Hericium erinaceus). Three flushes of pink oyster mushrooms and a first flush of lion's mane mushroom were analysed regarding their nutritional composition and whether they are suitable shrimp alternatives. The two mushrooms are rich in proteins (∼32% and ∼26% w/w for the first flush of pink oyster and lion's mane, respectively). The protein content of pink oyster mushroom decreased and the dietary fibre content increased across the different flushes. The antioxidants in the mushrooms were extracted using different methods, whereby aqueous extracts mostly excelled in terms of antioxidant activity. Hydrolysis confirmed the presence of conjugated p-coumaric acid in both mushrooms and possibly conjugated caffeic acid in pink oyster. Texture analysis results of the prototypes were close to the values of fried shrimp. However, although the sensory qualities of the final prototypes were perceived as similar to shrimp, further improvements in the recipe are necessary to make the prototypes indistinguishable from shrimp.

Sustainable production and pharmaceutical applications of β-glucan from microbial sources

β-glucans are a large class of complex polysaccharides found in abundant sources. Our dietary sources of β-glucans are cereals that include oats and barley, and non-cereal sources can consist of mushrooms, microalgae, bacteria, and seaweeds. There is substantial clinical interest in β-glucans; as they can be used for a variety of diseases including cancer and cardiovascular conditions. Suitable sources of β-glucans for biopharmaceutical applications include bacteria, microalgae, mycelium, and yeast. Environmental factors including culture medium can influence the biomass and ultimately β-glucan content. Therefore, cultivation conditions for the above organisms can be controlled for sustainable enhanced production of β-glucans. This review discusses the various sources of β-glucans and their cultivation conditions that may be optimised to exploit sustainable production. Finally, this article discusses the immune-modulatory potential of β-glucans from these sources.

The Mushroom Glucans: Molecules of High Biological and Medicinal Importance

Carbohydrates, including polysaccharide macromolecules, are the main constituents of the fungal cell wall. Among these, the homo- or heteropolymeric glucan molecules are decisive, as they not only protect fungal cells but also have broad, positive biological effects on the animal and human bodies. In addition to the beneficial nutritional properties of mushrooms (mineral elements, favorable proteins, low fat and energy content, pleasant aroma, and flavor), they have a high glucan content. Folk medicine (especially in the Far East) used medicinal mushrooms based on previous experience. At the end of the 19th century, but mainly since the middle of the 20th century, progressively more scientific information has been published. Glucans from mushrooms are polysaccharides that contain sugar chains, sometimes of only one kind (glucose), sometimes having several monosaccharide units, and they have two (α and β) anomeric forms (isomers). Their molecular weights range from 10⁴ to 10⁵ Da, and rarely 10⁶ Da. X-ray diffraction studies were the first to determine the triple helix configuration of some glucans. It seems that the existence and integrity of the triple helix structure are criteria for their biological effects. Different glucans can be isolated from different mushroom species, and several glucan fractions can be obtained. The biosynthesis of glucans takes place in the cytoplasm, the processes of initiation and then chain extension take place with the help of the glucan synthase enzyme complex (EC 2.4.1.34), and the sugar units are provided by sugar donor UDPG molecules. The two methods used today for glucan determination are the enzymatic and Congo red methods. True comparisons can only be made using the same method. Congo red dye reacts with the tertiary triple helix structure, and the resulting glucan content better reflects the biological value of glucan molecules. The biological effect of β-glucan molecules is proportional to the integrity of the tertiary structure. The glucan contents of the stipe exceed the values of the caps. The glucan levels of individual fungal taxa (including varieties) differ quantitatively and qualitatively. This review presents in more detail the glucans of lentinan (from Lentinula edodes), pleuran (from Pleurotus ostreatus), grifolan (from Grifola frondose), schizophyllan (from Schizophyllum commune), and krestin (from Trametes versicolor), along with their main biological effects.

Effects of fungal based bioactive compounds on human health: Review paper

Since the first years of history, microbial fermentation products such as bread, wine, yogurt and vinegar have always been noteworthy regarding their nutritional and health effects. Similarly, mushrooms have been a valuable food product in point of both nutrition and medicine due to their rich chemical components. Alternatively, filamentous fungi, which can be easier to produce, play an active role in the synthesis of some bioactive compounds, which are also important for health, as well as being rich in protein content. Therefore, this review presents some important bioactive compounds (bioactive peptides, chitin/chitosan, β-glucan, gamma-aminobutyric acid, L-carnitine, ergosterol and fructooligosaccharides) synthesized by fungal strains and their health benefits. In addition, potential probiotic- and prebiotic fungi were researched to determine their effects on gut microbiota. The current uses of fungal based bioactive compounds for cancer treatment were also discussed. The use of fungal strains in the food industry, especially to develop innovative food production, has been seen as promising microorganisms in obtaining healthy and nutritious food.

Evaluating comparative β-glucan production aptitude of Saccharomyces cerevisiae, Aspergillus oryzae, Xanthomonas campestris, and Bacillus natto

β-glucan is a natural polysaccharide derivative composed of a group of glucose monomers with β-glycoside bonds that can be synthesized intra- or extra-cellular by various microorganisms such as yeasts, bacteria, and moulds. The study aimed to discover the potential of various microorganisms such as Saccharomyces cerevisiae, Aspergillus oryzae, Xanthomonas campestris, and Bacillus natto in producing β-glucan. The experimental method used and the data were analyzed descriptively. The four microorganisms above were cultured under a submerged state in Yeast glucose (YG) broth for 120 h at 30 °C with 200 rpm agitation. During the growth, several parameters were examined including total population by optical density, the pH, and glucose contents of growth media. β-glucan was extracted using acid-alkaline methods from the growth media then the weight was measured. The results showed that S. cerevisiae, A. oryzae X. campestris, and B. natto were prospective for β-glucans production in submerged fermentation up to 120 h. The highest β-glucans yield was shown by B. natto (20.38%) with the β-glucans mass of 1.345 ± 0.08 mg and globular diameter of 600 μm. The highest β-glucan mass was achieved by A. oryzae of 82.5 ± 0.03 mg with the total population in optical density of 0.1246, a final glucose level of 769 ppm, the pH of 6.67, and yield of 13.97% with a globular diameter of 1400 μm.

Recent advances in enzymatic synthesis of β-glucan and cellulose

Bottom-up synthesis of β-glucans such as callose, fungal β-(1,3)(1,6)-glucan and cellulose, can create the defined compounds that are needed to perform fundamental studies on glucan properties and develop applications. With the importance of β-glucans and cellulose in high-profile fields such as nutrition, renewables-based biotechnology and materials science, the enzymatic synthesis of such relevant carbohydrates and their derivatives has attracted much attention. Here we review recent developments in enzymatic synthesis of β-glucans and cellulose, with a focus on progress made over the last five years. We cover the different types of biocatalysts employed, their incorporation in cascades, the exploitation of enzyme promiscuity and their engineering, and reaction conditions affecting the production as well as in situ self-assembly of (non)functionalised glucans. The recent achievements in the application of glycosyl transferases and β-1,4- and β-1,3-glucan phosphorylases demonstrate the high potential and versatility of these biocatalysts in glucan synthesis in both industrial and academic contexts.

Improved production of β-glucan by a T-DNA-based mutant of Aureobasidium pullulans

To improve β-1,3-1,6-D-glucan (β-glucan) production by Aureobasidium pullulans, an Agrobacterium tumefaciens-mediated transformation method was developed to screen a mutant A. pullulans CGMCC 19650. Based on thermal asymmetric-interlaced PCR detection, DNA sequencing, BLAST analysis, and quantitative real-time PCR assay, the T-DNA was identified to be inserted in the coding region of mal31 gene, which encodes a sugar transporter involved in pullulan biosynthesis in the mutant. The maximal biomass and β-glucan production under batch fermentation were significantly increased by 47.6% and 78.6%, respectively, while pullulan production was decreased by 41.7% in the mutant, as compared to the parental strain A. pullulans CCTCC M 2012259. Analysis of the physiological mechanism of these changes revealed that mal31 gene disruption increased the transcriptional levels of pgm2, ugp, fks1, and kre6 genes; increased the amounts of key enzymes associated with UDPG and β-glucan biosynthesis; and improved intracellular UDPG contents and energy supply, all of which favored β-glucan production. However, the T-DNA insertion decreased the transcriptional levels of ags2 genes, and reduced the biosynthetic capability to form pullulan, resulting in the decrease in pullulan production. This study not only provides an effective approach for improved β-glucan production by A. pullulans, but also presents an accurate and useful gene for metabolic engineering of the producer for efficient polysaccharide production. KEY POINTS: • A mutant A. pullulans CGMCC 19650 was screened by using the ATMT method. • The mal31 gene encoding a sugar transporter was disrupted in the mutant. • β-Glucan produced by the mutant was significantly improved.

3D Bioprinting of Lignocellulosic Biomaterials

The interest in bioprinting of sustainable biomaterials is rapidly growing, and lignocellulosic biomaterials have a unique role in this development. Lignocellulosic materials are biocompatible and possess tunable mechanical properties, and therefore promising for use in the field of 3D-printed biomaterials. This review aims to spotlight the recent progress on the application of different lignocellulosic materials (cellulose, hemicellulose, and lignin) from various sources (wood, bacteria, and fungi) in different forms (including nanocrystals and nanofibers in 3D bioprinting). Their crystallinity, leading to water insolubility and the presence of suspended nanostructures, makes these polymers stand out among hydrogel-forming biomaterials. These unique structures give rise to favorable properties such as high ink viscosity and strength and toughness of the final hydrogel, even when used at low concentrations. In this review, the application of lignocellulosic polymers with other components in inks is reported for 3D bioprinting and identified supercritical CO₂ as a potential sterilization method for 3D-printed cellulosic materials. This review also focuses on the areas of potential development by highlighting the opportunities and unmet challenges such as the need for standardization of the production, biocompatibility, and biodegradability of the cellulosic materials that underscore the direction of future research into the 3D biofabrication of cellulose-based biomaterials.

Triton X-100 improves co-production of β-1,3-D-glucan and pullulan by Aureobasidium pullulans

The effects of several surfactants on the biosynthesis of β-1,3-D-glucan (β-glucan) and pullulan by Aureobasidium pullulans CCTCC M 2012259 were investigated, and Triton X-100 was found to decrease biomass formation but increase β-glucan and pullulan production. The addition of 5 g/L Triton X-100 to the fermentation medium and bioconversion broth significantly increased β-glucan production by 76.6% and 69.9%, respectively, when compared to the control without surfactant addition. To reveal the physiological mechanism underlying the effect of Triton X-100 on polysaccharides production, the cell morphology and viability, membrane permeability, key enzyme activities, and intracellular levels of UDPG, NADH, and ATP were determined. The results indicated that Triton X-100 increased the activities of key enzymes involved in β-glucan and pullulan biosynthesis, improved intracellular UDPG and energy supply, and accelerated the transportation rate of precursors across the cell membrane, all of which contributed to the enhanced production of β-glucan and pullulan. Moreover, a two-stage culture strategy with combined processes of batch fermentation and bioconversion was applied, and co-production of β-glucan and pullulan in the presence of 5 g/L Triton X-100 additions was further improved. The present study not only provides insights into the effect of surfactant on β-glucan and pullulan production but also presents a feasible approach for efficient production of analogue exopolysaccharides. KEY POINTS: • Triton X-100 increased β-glucan and pullulan production under either batch fermentation or bioconversion. • Triton X-100 increased the permeability of cell membrane and accelerated the transportation rate of precursors across cell membrane. • Activities of key enzymes involved in β-glucan and pullulan biosynthesis were increased in the presence of Triton X-100. • Intracellular UDPG levels and energy supply were improved by Triton X-100 addition.

Effect of Strain, Wood Substrate and Cold Treatment on the Yield and β-Glucan Content of Ganoderma lucidum Fruiting Bodies

Wood residues from forestry industries can be potential raw materials for specialty and edible mushroom production. The aim of this study was to evaluate the suitability of wood residues for the cultivation of Ganoderma lucidum originating from boreal forests. The substrates tested included sawdust and wood chips of Betula spp., Populus tremula, Picea abies, Pinus sylvestris and Larix sp. The suitability of the substrates and the ability of the strains to develop fruiting bodies and produce β-glucan were evaluated. Fruiting body formation was supported by applying two different cold shock treatments to substrate bags. The highest yields were observed with MUS192 strain and Betula spp. and P. tremula wood-based substrates. β-Glucan content in the fruiting bodies was highest with the MUS75 and P. tremula wood-based substrate. Based on these findings, the combination of P. tremula wood residues and the MUS192 strain is proposed to enhance the yield and β-glucan content of the fruiting bodies. A cold treatment of 5 °C is suggested to induce primordia formation and to increase fruiting probability. This is the first time that strains of G. lucidum originating from boreal forests have been compared and successfully cultivated simulating commercial indoor cultivation.

Polysaccharides from Cordyceps miltaris cultured at different pH: Sugar composition and antioxidant activity

In the study, the β-glucan content, the primary structure and the antioxidant capacity of polysaccharides in Cordyceps militaris cultivated with different initial growth pH were evaluated. Meanwhile, the mechanism of β-glucan biosynthesis was investigated by RNA-Seq. Based on the results, C. militaris growing at an initial growth pH of 5-7 (CMsA) was distinguished from C. militaris growing at an initial growth pH of 8-9 (CMsB) and their unigenes showed the comparable expression. The mean of β-glucan content of CMsB group was 32.7% (w/w), 10% higher than that of CMsA. The results of RNA-seq showed 1088 differentially expressed genes between CMsA and CMsB groups. Furthermore, oxidative phosphorylation-related Gene ontology terms were up-regulated in CMsB groups. In addition, the results of structural analysis (FTIR spectrum, monosaccharide composition, periodate oxidation) and bioactivity evaluation speculated that C. militaris polysaccharides possessed higher β-(1 → 6)-glucan content and antioxidant activities in CMsB groups.

The scale-up cultivation of Candida utilis in waste potato juice water with glycerol affects biomass and β(1,3)/(1,6)-glucan characteristic and yield

New ideas on production of yeast origin β-glucan preparations for industrial application are attracting interest considering market development of that high-value functional polysaccharide. Sellecting an efficient yeast producer and designing culture conditions are a prerequisite for obtaining high yield of β-glucan. The aim of this study was to describe at the first time the influence of the mode of cultivation (shake-flasks and batch fermentation) and time of culture on characteristic and yield of biomass and β(1,3)/(1,6)-glucan preparations of Candida utilis ATCC 9950 after cultivation in medium based on waste potato juice water supplemented with 10% of glycerol. After shake-flask culture, the biomass was characterized by higher protein content (app. 26.5%) compared to 19% after batch fermentation while the cultivation on a biofermentor scale promoted polysaccharides biosynthesis. The highest output of purified β(1,3)/(1,6)-glucan preparation (5.3 g_d.w./L), containing app. 85% of that polysaccharide, was found after 48 h cultivation in biofermentor. Batch fermentation promoted biosynthesis of alkali-insoluble β(1,3)/(1,6)-glucan fraction, decreasing the content of β(1,6)-glucan. The yield of β(1,3)/(1,6)-glucan synthesis was 0.063 (g/g glycerol), while the productivity of that polysaccharide reached 0.094 (g/L/h). Longer batch fermentation (72 h) resulted in reduction of production efficiency of β-glucan preparation under studied conditions. The results of the study provide a new efficient biotechnological solution to produce high-value β-glucan preparations of C. utilis origin based on valorization of agro-waste potato juice water with glycerol.