Development of an Efficient Strategy to Improve Extracellular Polysaccharide Production of Ganoderma lucidum Using L-Phenylalanine as an Enhancer

The Performance and Evolutionary Mechanism of Ganoderma lucidum in Enhancing Selenite Tolerance and Bioaccumulation

BACKGROUND

Selenium (Se) pollution poses serious threats to terrestrial ecosystems. Mushrooms are important sources of Se with the potential for bioremediation. Pre-eminent Se resources must possess the ability to tolerate high levels of Se. To obtain Se-accumulating fungi, we isolated selenite-tolerance-enhanced Ganoderma lucidum JNUSE-200 through adaptive evolution.

METHODS

The molecular mechanism responsible for selenite tolerance and accumulation was explored in G. lucidum JNUSE-200 by comparing it with the original strain, G. lucidum CGMCC 5.26, using a combination of physiological and transcriptomic approaches.

RESULTS

G. lucidum JNUSE-200 demonstrated tolerance to 200 mg/kg selenite in liquid culture and exhibited normal growth, whereas G. lucidum CGMCC 5.26 experienced reduced growth, red coloration, and an unpleasant odor as a result of exposure to selenite at the same concentration. In this study, G. lucidum JNUSE-200 developed a triple defense mechanism against high-level selenite toxicity, and the key genes responsible for improved selenite tolerance were identified.

CONCLUSIONS

The present study offers novel insights into the molecular responses of fungi towards selenite, providing theoretical guidance for the breeding and cultivation of Se-accumulating varieties. Moreover, it significantly enhances the capacity of the bio-manufacturing industry and contributes to the development of beneficial applications in environmental biotechnology through fungal selenite transformation bioprocesses.

Optimization of chemical conditions for metabolites production by Ganoderma lucidum using response surface methodology and investigation of antimicrobial as well as anticancer activities

Ganoderma lucidum (G. lucidum) is a medicinal mushroom that is known for its ability to produce compounds with physiological effects on human health. This research was undertaken to amplify the production of bioactive components of G. lucidum under optimal cultivation conditions, obtained in a submerged state and utilized in solid state fermentation, with the purpose of enhancing antimicrobial and anticancer activities. The results indicated that titanium dioxide (TiO2 NPs), magnesium oxide nanoparticles (MgO2 NPs), and B6, along with glucose syrup and CLS syrups, were the most effective for producing GA, while wheat starch and whey protein, along with MgO2 NPs and B6 vitamin, stimulated polysaccharide production using the One Factor at a Time (OFAT) method. After screening, the response surface method (RSM) statistically indicated that the media containing 42.11 g/L wheat starch with 22 g/L whey protein and 50 g/L glucose syrup with 30 g/L CSL were found to be the best conditions for polysaccharide (21.47% of dry weight biomass) and GA (20.35 mg/g dry weight biomass) production, respectively. The moss of the fruit body of G. lucidum produced under optimal GA conditions had the highest diversity in flavonoids and phenolic acids and significant antimicrobial activity against Esherichia coli (E. coli) and Bacillus subtilis (B. subtilis). In addition, the IC50 levels of shell and stem of G. lucidum were 465.3 and 485.7 μg/mL, respectively, while the moss did not reach 50% inhibition. In the end, the statistical approaches utilized in this research to elevate the levels of bioactive components in the fruiting body of G. lucidum produced a promising natural source of antimicrobial and anticancer agents.

Improved laccase production by Trametes versicolor using Copper-Glycyl-L-Histidyl-L-Lysine as a novel and high-efficient inducer

A highly efficient strategy using Copper-Glycyl-L-Histidyl-L-Lysine (GHK-Cu) as a novel inducer was developed to enhance laccase production by Trametes versicolor. After medium optimization, laccase activity increased by 12.77-fold compared to that without GHK-Cu. The laccase production of 1113.8 U L-1 was obtained by scaling-up culture in 5-L stirring tank. The laccase production induced by CuSO4 was poorer than that of GHK-Cu at the same mole concentration. GHK-Cu could increase the permeability of cell membrane with less damage, and it facilitated the adsorption, accumulation, and utilization of copper by fungal cells, which was beneficial for laccase synthesis. GHK-Cu induced better expression of laccase related genes than that of CuSO4, resulting in higher laccase production. This study provided a useful method for induced production of laccase by applying GHK chelated metal ion as a non-toxic inducer, which reduced the safety risk of laccase broth and provided the potential application of crude laccase in food industry. In addition, GHK can be used as the carrier of different metal ions to enhance the production of other metalloenzymes.

A new strategy to improve Ganoderma polysaccharides production by symbiotic fungi elicitors through activating the biosynthetic pathway

Ganoderma lucidum polysaccharides (GLP) attract growing attention due to their remarkable bioactivities, but the low content in raw materials remains a bottleneck severely restricting their application. We previously found a higher polysaccharides accumulation in Ganoderma lucidum cultured in continuous cropping soil, and soil symbiotic fungi are presumed as the key among many factors. Herein, 33 symbiotic fungi were isolated from the soil, and fungal elicitors were prepared to investigate their biotic eliciting effect on GLP biosynthesis. Most elicitors were found to significantly improve GLP production, among which the NO.16 molecularly identified as Penicillium citrinum, exhibited the optimum eliciting effect with GLP yield increasing by 3.4 times. Differences in the biosynthetic pathway genes expressions and the monosaccharide components of GLP were further analyzed. The transcriptions of the main genes of GLP biosynthetic pathway were up-regulated under PCE treatments, suggesting it improves GLP production by activating transcriptions of the biosynthetic pathway genes. Moreover, PCE eliciting significantly altered the monosaccharide compositions of GLP with Gal, Man, GalA, GlcA, and Fuc increasing by 8.17 %, 5.68 %, 5.41 %, 2.66 %, and 1.51 % respectively, but Glc decreased by 23.43 %, which may result in the activity change. It can serve as a new strategy to improve GLP production.

Increasing the production of the bioactive compounds in medicinal mushrooms: an omics perspective

Macroscopic fungi, mainly higher basidiomycetes and some ascomycetes, are considered medicinal mushrooms and have long been used in different areas due to their pharmaceutically/nutritionally valuable bioactive compounds. However, the low production of these bioactive metabolites considerably limits the utilization of medicinal mushrooms both in commerce and clinical trials. As a result, many attempts, ranging from conventional methods to novel approaches, have been made to improve their production. The novel strategies include conducting omics investigations, constructing genome-scale metabolic models, and metabolic engineering. So far, genomics and the combined use of different omics studies are the most utilized omics analyses in medicinal mushroom research (both with 31% contribution), while metabolomics (with 4% contribution) is the least. This article is the first attempt for reviewing omics investigations in medicinal mushrooms with the ultimate aim of bioactive compound overproduction. In this regard, the role of these studies and systems biology in elucidating biosynthetic pathways of bioactive compounds and their contribution to metabolic engineering will be highlighted. Also, limitations of omics investigations and strategies for overcoming them will be provided in order to facilitate the overproduction of valuable bioactive metabolites in these valuable organisms.

Dragon fruit-kiwi fermented beverage: In vitro digestion, untargeted metabolome analysis and anti-aging activity in Caenorhabditis elegans

The research on the development of dragon fruit and kiwi fruit through LAB-yeast compound fermentation is very limited, and there are few related fermentation products on the market. The purpose of this study was to evaluate the stability of the antioxidant capacity of fermented beverages (FB) through in vitro simulated digestion, to evaluate the changes in metabolites of juice after fermentation through untargeted metabolomics, and used Caenorhabditis elegans as a model to evaluate its anti-aging activity. The results showed that FB not only has good in vitro antioxidant activity, but also the total phenol content (TPC), total flavonoid content (TFC), ABTS scavenging ability, and hydroxyl radical scavenging ability of FB were significantly increased during gastric digestion and intestinal digestion. Metabolomics showed that the contents of phenols and flavonoids related to antioxidant increased after fermentation, and fermentation had a significant effect on organic acids and amino acids in FB. Finally, compared with the control group, although the original concentration of FB has a side-toxic effect on nematodes, the mean lifespan of C. elegans fed with 1.56% FB increased by 18.01%, SOD activity significantly increased by 96.16% and MDA content significantly decreased by 40.62%. FB has good antioxidant activity in vitro and in vivo, and the antioxidant activity is stable during the simulated digestion process.

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.

Effect of surfactants on the production of polysaccharides from Schizophyllum commune through submerged fermentation

Schizophyllum commune (S. commune) polysaccharides are biomacromolecules with multiple biological activities and wide applications. In this study, polysaccharide production through submerged fermentation of S. commune using different surfactants was investigated. The addition of 1 g/L of polyoxyethylene sorbitan monooleate (Tween 80) at the beginning of the fermentation showed the best promotional effects on collective exopolysaccharide (EPS) production (which increased by 37.17%) while shortening the production cycle by 2 days. The monosaccharide composition of the EPS produced when the added Tween 80 was similar to that of the control; however, the molecular weight (Mw) was lower. Notably, the addition of Tween 80 significantly increased the ATP levels and the transcription levels of phosphoglucomutase and β-glucan synthase genes in the polysaccharide synthesis pathway. The addition of Tween 80 reduced the pellet size of the mycelium compared to that of the control, but did not significantly change the microstructure of the mycelial cells. This study proposes an efficient strategy for the production of polysaccharides through submerged fermentation of S. commune, and elucidates the detailed mechanism of using Tween 80 as a fermentation stimulatory reagent.

Roles of Small Subunits of Laccase (ssPOXA3a/b) in Laccase Production by Pleurotus eryngii var. ferulae

The small subunit, ssPOXA3a/b, and the large subunit, POXA3, are indispensable components of typical heterodimeric laccase (Lacc2) in white rot fungi. However, the enzymatic and biological functions of ssPOXA3a/b remain unclear. The present study revealed that neither ssPOXA3a nor ssPOXA3b per se has a catalytic ability, whereas their combination with POXA3 (and especially ssPOXA3b) enhances the activity, thermostability, and pH stability of POXA3. In Pleurotus eryngii var. ferulae, there was no regulatory relationship between ssPOXA3a/b and POXA3 at the transcriptional level. However, sspoxa3a/b overexpression had a negative feedback effect on lacc6 transcription. By contrast, poxa3 transcripts had no effect on any other laccase isoenzyme. Overexpression of sspoxa3a/b resulted in small fungal pellets, thin mycelial walls, and facilitated laccase secretion. However, poxa3 overexpression had no influence on pellet morphology. Collectively, this work elucidated the functions of ssPOXA3a/b and laid an empirical foundation for the development of high-yield laccase.

Influence of Selenium Biofortification on the Growth and Bioactive Metabolites of Ganoderma lucidum

Selenium biofortification of edible and medicinal mushrooms is an effective way to produce selenium-enriched food supplements. Ganoderma lucidum is the typical one with excellent biological activity. This study investigated G. lucidum growth and bioactive metabolites alterations during liquid culture with different concentrations of selenite. Low selenium levels did not affect growth and mycelia morphology, whereas high selenium levels negatively influenced growth, dramatically decreased biomass, caused nucleic acid and protein leakage, damaged cell walls and membranes, and resulted in indicators such as degraded cells, a red color, and an unpleasant odor. Through headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) analysis, ten volatile Se compounds were identified in G. lucidum with 200 ppm selenite, which led to an odor change, whereas only three with 50 ppm selenite. SeMet was the major selenoamino acid in the 50 ppm selenite group by high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), but more MeSeCys was produced with 200 ppm selenite. Polysaccharide yields were promoted and inhibited with 50 and 200 ppm selenite, respectively. These results provide comprehensive insights into the effects of selenite on G. lucidum in liquid culture and are beneficial for functional selenium-enriched mushroom production and improving nutritive values.

Enhancement of exopolysaccharide production from Ganoderma lucidum using a novel submerged volatile co-culture system

Based on the impact of volatile organic compounds (VOCs) on secondary metabolite pathways, a novel submerged volatile co-culture system was constructed, and the effects of thirteen fungal and bacterial VOCs were investigated on Ganoderma lucidum exopolysaccharides production. The results demonstrated at least a 2.2-fold increase in exopolysaccharide (EPS) specific production yield in 6 days submerged volatile co-culture of G. lucidum with Pleurotus ostreatus. Therefore, P. ostreatus was selected as a variable culture, and the effects of agitation speed, inoculum size, initial pH, and co-culture volume on EPSs production were investigated using a Taguchi L₉ orthogonal array. Finally, the highest concentration of EPSs (3.35 ± 0.22 g L^-1) was obtained under optimized conditions; initial pH 5.0, inoculum size 10%, 150 rpm, and 3:1 volume ratio of variable culture to main culture.

Transcriptome dynamics and metabolite analysis revealed the candidate genes and regulatory mechanism of ganoderic acid biosynthesis during liquid superficial-static culture of Ganoderma lucidum

Ganoderic acid (GA), an important secondary metabolite of Ganoderma lucidum, exhibited many significant pharmacological activities. In this study, the biosynthetic mechanism of GAs was investigated by comparing metabolites and transcriptome dynamics during liquid superficial‐static culture (LSSC) and submerged culture (SC). LSSC was a better method to produce GA because thirteen GAs were identified from mycelia by UPLC‐QTOF‐MS, and the content of all GAs was higher in LSSC than in SC. Ergosterol was accumulated during the SC process in G. lucidum. Transcriptome dynamics analysis revealed CYP5150L8 was the key gene regulating lanosterol flux into GA biosynthesis. Other sixteen CYP450 genes were significantly higher expressed during the culture time in LSSC and could be potential candidate genes associated with the biosynthesis of different GAs. In addition, six of the ten expressed genes in ergosterol biosynthetic pathway shown upregulated at some time points in SC. These results not only provide a fundamental information of the key genes in ergosterol and GA biosynthetic pathway, but also provide directions for future elucidating the regulatory mechanisms of GAs in G. lucidum and enabling us to promote the development and utilization of LSSC at the industrial level.

Immunomodulatory activities of polysaccharides from Ganoderma on immune effector cells

Polysaccharides are the most abundant bioactive compounds in Ganoderma and have been widely used as dietary supplements in traditional Chinese medicine for thousands of years. Polysaccharides from Ganoderma exhibit unique biological properties, including anti-tumor, anti-inflammatory, and immunomodulatory activities. Herein, the sources and structures of polysaccharides from Ganoderma were presented. This work also reviews the immunomodulatory activities and possible mechanisms of polysaccharides from Ganoderma on different immune effector cells, including lymphocytes and myeloid cells. As an available adjunctive remedy, polysaccharides from Ganoderma can potentially be applied for the modulation of the host immune system, namely the innate immunity, the cellular immunity, and the humoral immunity.

Enhanced exopolysaccharide production in submerged fermentation of Ganoderma lucidum by Tween 80 supplementation

Bioactive polysaccharides extracted from Ganoderma lucidum (G. lucidum) have been widely applied in food and medicine for their multiple functions. In this study, G. lucidum exopolysaccharide (EPS) production in submerged fermentation was stimulated by Tween 80. The addition of 0.25% Tween 80 on day 3 gave a maximum production of mycelial biomass and EPS, with an increase of 19.76 and 137.50%, respectively. Analysis of fermentation kinetics showed that glucose was consumed faster after adding Tween 80, while the expression of EPS biosynthesis-related genes and ATP generation were greatly improved. Moreover, Tween 80 resulted in the significant accumulation of reactive oxygen species and increased cell membrane and cell wall permeability. The EPS from Tween 80-containing medium had higher contents of carbohydrate and uronic acid, lower molecular weight, and higher antioxidant activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals than those of EPS produced in the absence of Tween 80. This study provides further evidence to clarify the stimulatory effects of Tween 80 in fermentation and provides a guide for the production of bioactive G. lucidum EPS.