Control of Grifola frondosa Morphology by Agitation and Aeration for Improving Mycelia and Exo-Polymer Production

Grifola frondosa polysaccharides: A review on structure/activity, biosynthesis and engineering strategies

Polysaccharides are the main polymers in edible fungi Grifola frondosa, playing a crucial role in the physiology and representing the healthy benefits for humans. Recent efforts have well elucidated the fine structures and biological functions of G. frondosa polysaccharides. The recently-rapid developments and increasing availability in fungal genomes also accelerated the better understanding of key genes and pathways involved in biosynthesis of G. frondosa polysaccharides. Herein, we provide a brief overview of G. frondosa polysaccharides and their activities, and comprehensively outline the complex process, genes and proteins corresponding to G. frondosa polysaccharide biosynthesis. The regulation strategies including strain improvement, process optimization and genetic engineering were also summarized for maximum production of G. frondosa polysaccharides. Some remaining unanswered questions in describing the fine synthesis machinery were also pointed out to open up new avenues for answering the structure-activity relationship and improving polysaccharide biosynthesis in G. frondosa. The review hopefully presents a reasonable full picture of activities, biosynthesis, and production regulation of polysaccharide in G. frondosa.

Submerged Culture of Edible and Medicinal Mushroom Mycelia and Their Applications in Food Products: A Review

Edible mushrooms have rich nutrition (e.g., proteins, dietary fibers, polysaccharides) and they can be potential sources of important ingredients in food processing. However, the cultivation of mushroom fruiting bodies needs a relatively long time, and they can be easily polluted during the growth process. At the same time, a lot of labor and larger planting areas are also required. As we all know, submerged fermentation is a good way to produce edible mushroom mycelia with less environmental pollution and small footprint, which are also rich in nutrition and bioactive components that are used as dietary supplements or health care products in the food industry. Therefore, it can be considered that the replacement of edible mushroom fruiting bodies with edible mushroom mycelia produced through submerged fermentation has great application potential in food production. At present, most of the research about edible mushroom mycelia focuses on the production of bioactive metabolites in fermentation liquid, but there are few reports that concentrate on their applications in food. This paper reviews the research progress of submerged culture of edible mushroom mycelia and their applications in food products.

Enhancement of functional activity and biosynthesis of exopolysaccharides in Monascus purpureus by genistein treatments

The exopolysaccharides (EPS) produced by the edible medicinal fungus Monascus purpureus (EMP) become the center of growing interest due to their techno-functional properties and their numerous applications in the food industries; however, the low EPS yields limit its application. In this study, the effect of genistein supplementation on the production, rheological and antioxidant properties of EPS by M. purpureus and its biosynthesis mechanism were explored. The results indicated that the addition of genistein (3 g/L) generated a 110% and 59% increase in the maximum mycelial biomass and EPS yield, respectively. The genistein supplementation group (G-EMP) had higher molar percentages of Xyl and Man, and significantly decreased molecule weight and particle size of EPS, which resulted in stronger antioxidant effect and cell growth promotion. Rheological analysis showed that both EMP and G-EMP demonstrated pseudoplastic fluid behavior and G-EMP exhibited strong gel-like elastic behavior (G' > G"). Furthermore, genistein not only facilitated the production of EPS by regulating cell membrane permeability, enhancing cellular respiratory metabolism and monosaccharide precursor synthesis pathways, and enhancing antioxidant enzyme activity to reduce oxidative stress damage, but also affected the composition of the monosaccharides by increasing enzyme activity in the underlying synthesis pathways. These findings expand the application of M. purpureus resources and provide a paradigm for future study of the structural and functional characteristics of EPS.

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Genistein (3 g/L) significantly stimulate yield of biomass and exopolysaccharides (EPS) from M. purpureus.

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The physicochemical and rheological properties of EPS were significantly changed.

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Their antioxidant and cytoprotective effect were compared.

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A possible mechanism for the response of genistein to increase EPS yield is proposed.

Enhancement of polysaccharides production using microparticle enhanced technology by Paraisaria dubia

Background

Polysaccharides are important active ingredients in Ophiocordyceps gracilis with many physiological functions. It can be obtained from the submerged fermentation by the anamorph (Paraisaria dubia) of Ophiocordyceps gracilis. However, it was found that the mycelial pellets of Paraisaria dubia were dense and increased in volume in the process of fermentation, and the center of the pellets was autolysis due to the lack of nutrient delivery, which extremely reduced the yield of polysaccharides. Therefore, it is necessary to excavate a fermentation strategy based on morphological regulation for Paraisaria dubia to promote polysaccharides accumulation.

Results

In this study, we developed a method for enhancing polysaccharides production by Paraisaria dubia using microparticle enhanced technology, talc microparticle as morphological inducer, and investigated the enhancement mechanisms by transcriptomics. The optimal size and dose of talc were found to be 2000 mesh and 15 g/L, which resulted in a high polysaccharides yield. It was found that the efficient synthesis of polysaccharides requires an appropriate mycelial morphology through morphological analysis of mycelial pellets. And, the polysaccharides synthesis was found to mainly rely on the ABC transporter-dependent pathway revealed by transcriptomics. This method was also showed excellent robustness in 5-L bioreactor, the maximum yields of intracellular polysaccharide and exopolysaccharides were 83.23 ± 1.4 and 518.50 ± 4.1 mg/L, respectively. And, the fermented polysaccharides were stable and showed excellent biological activity.

Conclusions

This study provides a feasible strategy for the efficient preparation of cordyceps polysaccharides via submerged fermentation with talc microparticles, which may also be applicable to similar macrofungi.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01733-w.

Stimulating mechanism of corn oil on biomass and polysaccharide production of Pleurotus tuber-regium mycelium

Hyperbranched polysaccharides (HBPSs) are the main components in cell wall and exopolysaccharide (EPS) of Pleurotus tuber-regium. To enhance the yield of these macromolecules, corn oil at 4% addition exhibited the best effect for production of mycelial biomass at 20.49 g/L and EPS at 0.59 g/L, which was 2.56 folds and 1.90 folds of the control, respectively. The treated hyphae were much thicker with smooth surface, while its cell wall content (43.81 ± 0.02%) was 1.96 times of the control (22.34 ± 0.01%). Moreover, a large number of lipid droplets could be visualized under the view of confocal laser scanning microscopy (CLSM). RNA-seq analysis revealed that corn oil could enter the cells and result in the up-regulation of genes on cell morphology and membrane permeability, as well as the down-regulation on expression level of polysaccharide hydrolase and genes involved in the MAPK pathway, all of which probably contribute to the increase of polysaccharides production.

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.

A critical review on submerged production of mushroom and their bioactive metabolites

Mushrooms are ubiquitous in nature. Even though humankind has been consuming mushrooms for ages, their medicinal and nutraceutical properties are not used to its fullest potential in the present market. Edible mushrooms are not only a cheap and nutritious option to mitigate malnutrition, but they also produce effective biomass. Submerged fermentation (SmF) is not only a cost-effective method to produce biomass along with exquisite bioactive metabolites but it also reduces the chances of contamination and the time of production. Therefore, this study unveils the bioactive metabolites being produced by mushrooms. Moreover, it also showcases the recent advances in the areas of bio-active compounds and their judicious implementations in daily life and pharmaceutical industries. Moreover, there is a distinct lack in utilizing the potential benefits of bioactive compounds from mushroom unless in vivo and in vitro studies are demonstrated.

UDP-glucose pyrophosphorylase gene affects mycelia growth and polysaccharide synthesis of Grifola frondosa

To elucidate potential roles of UDP-glucose pyrophosphorylase (UGP) in mycelial growth and polysaccharide synthesis of Grifola frondosa, a putative 2036-bp UDP-glucose pyrophosphorylase gene gfugp encoding a 53.17-kDa protein was cloned and re-annotated. Two dual promoter RNA silencing vectors of pAN7-iUGP-P-dual and pAN7-iUGP-C-dual were constructed to down-regulate gfugp expression by targeting its promoter or conserved functional sequences, respectively. Results showed that silence of gfugp promoter sequence had a higher down-regulating efficiency with slower mycelial growth and polysaccharide production than those of conserved sequence. The monosaccharide compositions/percentages of mycelial and exo-polysaccharides significantly changed with the increase of galactose and arabinose contents possibly due to block of UDP-glucose supply by gfugp silence and alteration of sugar metabolism via up-regulation of UDP-glucose-4-epimerase (gfuge) and UDP-xylose-4-epimerase (gfuxe) transcription. Our findings would provide a reference to know the biosynthesis pathway of mushroom polysaccharides and improve their production by metabolic regulation.

Functions of a Glucan Synthase Gene GFGLS in Mycelial Growth and Polysaccharide Production of Grifola frondosa

Glucan synthase (GLS) gene is known to be involved in the fungal biosynthesis of cell wall, differentiation, and growth. In the present study, a glucan synthase gene (GFGLS) in the edible mushroom Grifola frondosa with a full sequence of 5927 bp encoding a total of 1781 amino acids was cloned and characterized for the first time. GFGLSp is a membrane protein containing two large transmembrane domains connected with a hydrophilic cytoplasmic domain. With a constructed dual promoter RNA silencing vector pAN7-gfgls-dual, a GFGLS-silencing transformant iGFGLS-3 had the lowest GFGLS transcriptional expression level (26.1%) with a shorter length and thinner appearance of the mycelia, as well as decreased mycelial biomass and exo-polysaccharide production of 5.02 and 0.38 g/L, respectively. Further analysis indicated that GFGLS silence influenced slightly the monosaccharide compositions and ratios of mycelial and exo-polysaccharide. These findings suggest that GFGLS could affect mycelial growth and polysaccharide production by downregulating the glucan synthesis.

Laccase production and pellet morphology of Coprinopsis cinerea transformants in liquid shake flask cultures

Laccase production and pellet formation of transformants of Coprinopsis cinerea strain FA2222 of C. cinerea laccase gene lcc1 subcloned behind the gpdII-promoter from Agaricus bisporus were compared with a control transformant carrying no extra laccase gene. At the optimum growth temperature of 37 °C, maximal laccase yields of 2.9 U/ml were obtained by the best lcc1 transformant pYSK7-26 in liquid shake flask cultures. Reduction in temperature to 25 °C increased laccase yields up to 9.2 U/ml. The control transformant had no laccase activities at 37 °C but native activity at 25 °C (3.5 U/ml). Changing the temperature had severe effects on the morphology of the mycelial pellets formed during cultivation, but links of distinct pellet morphologies to native or recombinant laccase production could not be established. Automated image analysis was used to characterise pellet formation and morphological parameters (pellet area, diameter, convexity and mycelial structure). Cross sections of selected pellets showed that they differentiated in an outer rind and an inner medulla of loosened hyphae. Pellets at 25 °C had a small and dense outer zone and adopted with time a smooth surface. Pellets at 37 °C had a broader outer zone and a fringy surface due to generation of more and larger protuberances in the rind that when released can serve for production of further pellets.

Genetic characterization, evaluation of growth and production of biomass of strains from wild edible mushrooms of Lyophyllum of Central Mexico

The present study conducted a genetic characterization and determined growth rate and biomass production in solid and liquid media, using strains obtained from wild edible sporomes of Lyophyllum that grow in high mountains. Vegetative isolation was used to obtain a total of four strains, which were divided into two clades within the section Difformia: Lyophyllum sp. and Lyophyllum aff. shimeji. Growth rate and biomass production were influenced by both the culture media and the strains. In a potato dextrose agar medium, the strains presented a higher growth rate, while in a malt extract-peptone and yeast agar medium, the growth rate was lower, but with a higher biomass production that was equal to that in the malt extract-peptone and yeast liquid medium.

Improved mycelia and polysaccharide production of Grifola frondosa by controlling morphology with microparticle Talc

Background

Mushroom showed pellet, clump and/or filamentous mycelial morphologies during submerged fermentation. Addition of microparticles including Talc (magnesium silicate), aluminum oxide and titanium oxide could control mycelial morphologies to improve mycelia growth and secondary metabolites production. Here, effect of microparticle Talc (45 μm) addition on the mycelial morphology, fermentation performance, monosaccharide compositions of polysaccharides and enzymes activities associated with polysaccharide synthesis in G. frondosa was well investigated to find a clue of the relationship between polysaccharide biosynthesis and morphological changes.

Results

Addition of Talc decreased the diameter of the pellets and increased the percentage of S-fraction mycelia. Talc gave the maximum mycelial biomass of 19.25 g/L and exo-polysaccharide of 3.12 g/L at 6.0 g/L of Talc, and mycelial polysaccharide of 0.24 g/g at 3.0 g/L of Talc. Talc altered the monosaccharide compositions/percentages in G. frondosa mycelial polysaccharide with highest mannose percentage of 62.76 % and lowest glucose percentage of 15.22 % followed with the corresponding changes of polysaccharide-synthesis associated enzymes including lowest UDP-glucose pyrophosphorylase (UGP) activity of 91.18 mU/mg and highest UDP-glucose dehydrogenase (UGDG) and GDP-mannose pyrophosphorylase (GMPPB) activities of 81.45 mU/mg and 93.15 mU/mg.

Conclusion

Our findings revealed that the presence of Talc significantly changed the polysaccharide production and sugar compositions/percentages in mycelial and exo-polysaccharides by affecting mycelial morphology and polysaccharide-biosynthesis related enzymes activities of G. frondosa.

The Online Morphology Control and Dynamic Studies on Improving Vitamin B12 Production by Pseudomonas denitrificans with Online Capacitance and Specific Oxygen Consumption Rate

The relationship between the morphological character of Pseudomonas denitrificans and vitamin B12 synthesis based on real-time capacitance measurement and online specific oxygen consumption rate (Q O2) control was established for enhancing vitamin B12 production. Results demonstrated that the threshold Q O2 value lower than 2.0 mmol/gDCW/l would greatly stimulate the state transfer from the cell number growth phase to the cell elongation phase and promote rapid vitamin B12 biosynthesis, while the vitamin B12 biosynthesis rate could also be inhibited when the rate of cell's length-to-width ratio (ratio-LW) was higher than 10:1. Furthermore, the optimal morphology controlling strategy was achieved based on online Q O2 control, which increases the appropriate active cell numbers at the former phase, and then control the elongation of ratio-LW no more than 10:1 at the vitamin B12 biosynthesis phase. The maximal vitamin B12 production reached 239.7 mg/l at 168 h, which was improved by 14.7 % compared with the control (208 mg/l). This online controlling strategy would be effectively applied for improving industrial vitamin B12 fermentation.