Effect of mycelial morphology on ergothioneine production during liquid fermentation of Lentinula edodes

Ergothioneine Production by Submerged Fermentation of a Medicinal Mushroom Panus conchatus

Ergothioneine is a natural and safe antioxidant that plays an important role in anti-aging and the prevention of various diseases. This study aimed to report on a kind of medicinal mushroom of Panus conchatus with great potential for the bioproduction of ergothioneine. The effect of different nutritional and environmental conditions on the growth of Panus conchatus and ergothioneine production were investigated. Molasses and soy peptone were found to promote cell growth of Panus conchatus and enhance ergothioneine accumulation. Adding precursors of histidine, methionine and cysteine could increase ergothioneine production and the highest ergothioneine concentration of 148.79 mg/L was obtained. Finally, the extraction and purification processes were also established to obtain the crude ergothioneine extract for further antioxidant property evaluation. The ergothioneine from Panus conchatus showed high antioxidant activity with good stability in a lower pH environment. This study provided a new strain and process for the bioproduction of ergothioneine.

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.

Recent Strategies for the Biosynthesis of Ergothioneine

Ergothioneine (EGT) is a unique naturally occurring amino acid that is usually biosynthesized by bacteria and fungi. As a food-derived antioxidant and cytoprotectant, it has several physiological benefits and has a wide range of applications in food, medicine, and cosmetics. Traditional production of EGT is mainly through biological extraction or chemical synthesis; however, these methods are inefficient, making large-scale production to meet the growing market demand difficult. Nowadays, the rapid development of synthetic biology has greatly accelerated the research on the EGT production by microbial fermentation. In this paper, the biological characteristics, applications, biosynthesis, separation, and detection methods of EGT were fully reviewed. Furthermore, the approaches and challenges for engineering microbial cells to efficiently synthesize EGT were also discussed. This work provides new ideas and future research potentials in EGT production.

Flexible Fungal Materials: Shaping the Future

Fungi are a revolutionary, smart, and sustainable manufacturing platform that can be used to upcycle byproducts and wastes into flexible fungal materials (FFMs) such as chitin- and β-glucan-based foams, paper, and textiles. With highly adaptable manufacturing pathways, the efficiency and properties of these materials depend on the biomass source and fermentation method. Liquid substrates provide fast, upscalable, and compact production processes but are susceptible to contamination and are limited to paper-like materials for printing, wound dressings, and membranes. Solid-state fermentation is cheaper but struggles to deliver homogeneous fungal growth and is used to produce fungal foams for packaging, insulation, textiles, and leather substitutes. The broad range of applications and uses of biological organisms in materials hallmarks fungi as forerunners in improving environmental sustainability globally.

The current status of biotechnological production and the application of a novel antioxidant ergothioneine

Ergothioneine is a sulfur-containing histidine derivative, that possessesexcellent antioxidant activity and has been used in the food and cosmetics industries. It plays a significant role in anti-aging and the prevention of various diseases. This review will briefly introduce the functions and applications of ergothioneine, elaborate the biosynthetic pathways of ergothioneine and describe several strategies to increase the production of ergothioneine. Then the efficient extraction and detection methods of ergothioneine will be presented. Finally, several proposals are put forward to increase the yield of ergothioneine, and the development prospects of ergothioneine will be discussed.

Construction of a genetic linkage map and detection of quantitative trait locus for the ergothioneine content in tamogitake mushroom (Pleurotus cornucopiae var. citrinopileatus)

Developing high-content strains of L-ergothioneine (EGT), an antioxidant amino acid, is an important breeding target for tamogitake mushroom, Pleurotus cornucopiae var. citrinopileatus. We constructed a genetic linkage map based on segregation analysis of markers in 105 F1 progenies. The loci of 245 markers, including 10 AFLP markers, 195 Rad markers, 2 mating type factors, and 38 gene markers, were mapped. The map contained 12 linkage groups with a total genetic distance of 906.8 cM, and an average marker interval of 4.0 cM. The population from crossing between tester monokaryon and F1 progenies was used to characterize quantitative trait loci (QTL) for EGT content. With composite interval mapping (CIM) method, QTL of EGT content were found to be located in linkage group 10, having a Logarithm of the odds (LOD) score of 2.53 with a 10.1% contribution rate. Moreover, a single nucleotide polymorphism (SNP), A/T, was identified in a gene region of the genome in the neighborhood where the QTL peak existed. This SNP genotype was in good agreement with the EGT phenotypes of each strain in the both QTL population and wild population. Thus, this SNP would have great potential value to use the marker-assisted selection (MAS) for this mushroom with high EGT content.

The biology of ergothioneine, an antioxidant nutraceutical

Ergothioneine (ERG) is an unusual thio-histidine betaine amino acid that has potent antioxidant activities. It is synthesised by a variety of microbes, especially fungi (including in mushroom fruiting bodies) and actinobacteria, but is not synthesised by plants and animals who acquire it via the soil and their diet, respectively. Animals have evolved a highly selective transporter for it, known as solute carrier family 22, member 4 (SLC22A4) in humans, signifying its importance, and ERG may even have the status of a vitamin. ERG accumulates differentially in various tissues, according to their expression of SLC22A4, favouring those such as erythrocytes that may be subject to oxidative stress. Mushroom or ERG consumption seems to provide significant prevention against oxidative stress in a large variety of systems. ERG seems to have strong cytoprotective status, and its concentration is lowered in a number of chronic inflammatory diseases. It has been passed as safe by regulatory agencies, and may have value as a nutraceutical and antioxidant more generally.

Molecular identification of Shiitake [Lentinula edodes Berk (Pegler)] and production of secondary metabolites with biotechnological potential

The Shitake mushroom (Lentinula edodes) is the second most-consumed mushroom in the world; in Colombia, it is cultivated and commercialized on a small scale in some supermarkets. Little is known about the precedence, nutritional and medicinal properties of Shiitake produced in Colombia. In this study, four shiitake isolates were grown in Colombia (LEUCO1, LEUCO2, LEUCO3, and LEUCO4) were sequenced in their ITS genes and evaluated for the production of three medicinal metabolites, eritadenine, ergotioneine and β-glucans (1,3-1, 6), using submerged culture. Genetic analysis revealed that all the isolates were close and related to the Japanese strain Cr62. LEUCO1 and LEUCO2 showed a distance of 0.000, as well as LEUCO3 and LEUCO4. All four isolates produced erythadenin in a range of 26.3-8.6 mg / L, with the best performance of LEUCO1 at 26.3 mg / L (p <0.05). Ergotioneine was produced with similar statistical yields in all the isolates with an average of 0.7 mg / g of dry weight biomass (DW). Β-glucans (1.3-1.6) were produced with yields of 5.6 - 3.8% of DW biomass, with the best values ​​for LEUCO2 and the lowest for LEUCO4 (p <0.05). In conclusion, we identified low genetic diversity in the four isolates, corresponding to two haplotypes with minimal genetic difference between them, related to the Japanese strain Cr62, indicating that Colombian farmers cultivate almost the same strains of shitake. Secondary metabolites, eritadenine, β-glucans and ergotioneine were found in promising yields useful for the pharmaceutical and food industries. More studies should be conducted to improve the yield of shitake metabolites through new growing conditions for industrial production and to find metabolic pathways and related genes.

Optimization of submerged culture conditions involving a developed fine powder solid seed for exopolysaccharide production by the medicinal mushroom Ganoderma lucidum

To facilitate Ganoderma lucidum submerged cultivation and achieve high productivity, four fine powder solid substrates incorporated with different nitrogen-rich supplements were utilized to grow the fungus and as solid seed for its submerged culture. Of the four solid seeds, the soybean meal solid seed gave the highest biomass (10.73 g/L) and exopolysaccharide (EPS) (1.22 g/L), higher than those (8.36 g/L biomass and 0.44 g/L EPS) obtained with mycelial liquid seed. The optimal level of soybean meal supplementation was 20% (w/w) for production of the solid seed. Following single factor experiments, levels of three selected process variables were optimized as: the moisture content of solid seed, 70%; inoculum size, 0.8 g/flask; and rotary speed, 160 rpm. These conditions were validated experimentally with improved EPS yield of 1.33 g/L. The developed solid seed can be conveniently used for G. lucidum submerged culture with improved EPS productivity.

Rocking Aspergillus: morphology-controlled cultivation of Aspergillus niger in a wave-mixed bioreactor for the production of secondary metabolites

Background

Filamentous fungi including Aspergillus niger are cell factories for the production of organic acids, proteins and bioactive compounds. Traditionally, stirred-tank reactors (STRs) are used to cultivate them under highly reproducible conditions ensuring optimum oxygen uptake and high growth rates. However, agitation via mechanical stirring causes high shear forces, thus affecting fungal physiology and macromorphologies. Two-dimensional rocking-motion wave-mixed bioreactor cultivations could offer a viable alternative to fungal cultivations in STRs, as comparable gas mass transfer is generally achievable while deploying lower friction and shear forces. The aim of this study was thus to investigate for the first time the consequences of wave-mixed cultivations on the growth, macromorphology and product formation of A. niger.

Results

We investigated the impact of hydrodynamic conditions on A. niger cultivated at a 5 L scale in a disposable two-dimensional rocking motion bioreactor (CELL-tainer^®) and a BioFlo STR (New Brunswick^®), respectively. Two different A. niger strains were analysed, which produce heterologously the commercial drug enniatin B. Both strains expressed the esyn1 gene that encodes a non-ribosomal peptide synthetase ESYN under control of the inducible Tet-on system, but differed in their dependence on feeding with the precursors d-2-hydroxyvaleric acid and l-valine. Cultivations of A. niger in the CELL-tainer resulted in the formation of large pellets, which were heterogeneous in size (diameter 300–800 μm) and not observed during STR cultivations. When talcum microparticles were added, it was possible to obtain a reduced pellet size and to control pellet heterogeneity (diameter 50–150 μm). No foam formation was observed under wave-mixed cultivation conditions, which made the addition of antifoam agents needless. Overall, enniatin B titres of about 1.5–2.3 g L⁻¹ were achieved in the CELL-tainer^® system, which is about 30–50% of the titres achieved under STR conditions.

Conclusions

This is the first report studying the potential use of single-use wave-mixed reactor systems for the cultivation of A. niger. Although final enniatin yields are not competitive yet with titres achieved under STR conditions, wave-mixed cultivations open up new avenues for the cultivation of shear-sensitive mutant strains as well as high cell-density cultivations.

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.

Snapshots of C-S Cleavage in Egt2 Reveals Substrate Specificity and Reaction Mechanism

Sulfur incorporation in the biosynthesis of ergothioneine, a histidine thiol derivative, differs from other well-characterized transsulfurations. A combination of a mononuclear non-heme iron enzyme-catalyzed oxidative C-S bond formation and a subsequent pyridoxal 5'-phosphate (PLP)-mediated C-S lyase reaction leads to the net transfer of a sulfur atom from a cysteine to a histidine. In this study, we structurally and mechanistically characterized a PLP-dependent C-S lyase Egt2, which mediates the sulfoxide C-S bond cleavage in ergothioneine biosynthesis. A cation-π interaction between substrate and enzyme accounts for Egt2's preference of sulfoxide over thioether as a substrate. Using mutagenesis and structural biology, we captured three distinct states of the Egt2 C-S lyase reaction cycle, including a labile sulfenic intermediate captured in Egt2 crystals. Chemical trapping and high-resolution mass spectrometry were used to confirm the involvement of the sulfenic acid intermediate in Egt2 catalysis.

Hyperproduction of exopolysaccharides by submerged mycelial culture of Ganoderma lucidum using a solid seed grown in fine-powder of wheat bran and in vitro evaluation of the antioxidant activity of the exopolysaccharides produced

To facilitate Ganoderma lucidum submerged culture and obtain high productivity, a fine powder of wheat bran was used to grow the fungus for solid-state fermentation and as solid seed for its submerged cultures. The results indicated that the optimal inoculum size was low, being 0.75 g in 250 mL-sized flasks containing 80 mL medium. The maximal exopolysaccharide concentration and biomass produced was 0.74 and 14.71 g/L, respectively, which is considerably higher than that obtained with the commonly used mycelial pellet liquid seed (0.47 and 8.56 g/L, respectively). The EPS and biomass productivity of the solid seed cultures decreased only slightly, even after a 6-month storage period. EPS produced showed higher antioxidant activity compared with that produced in the liquid seed cultures. The developed solid seed can serve as a ready-to-use inoculum for long-term use in G. lucidum submerged culture for the hyperproduction of highly bioactive EPS and biomass.

The Taming of the Shrew--Controlling the Morphology of Filamentous Eukaryotic and Prokaryotic Microorganisms

One of the most sensitive process characteristics in the cultivation of filamentous biological systems is their complex morphology. In submerged cultures, the observed macroscopic morphology of filamentous microorganisms varies from freely dispersed mycelium to dense spherical pellets consisting of a more or less dense, branched and partially intertwined network of hyphae. Recently, the freely dispersed mycelium form has been in high demand for submerged cultivation because this morphology enhances the growth and production of several valuable products. A distinct filamentous morphology and productivity are influenced by the environment and can be controlled by inoculum concentration, spore viability, pH value, cultivation temperature, dissolved oxygen concentration, medium composition, mechanical stress or process mode as well as through the addition of inorganic salts or microparticles, which provides the opportunity to tailor a filamentous morphology. The suitable morphology for a given bioprocess varies depending on the desired product. Therefore, the advantages and disadvantages of each morphological type should be carefully evaluated for every biological system. Because of the high industrial relevance of filamentous microorganisms, research in previous years has aimed at the development of tools and techniques to characterise their growth and obtain quantitative estimates of their morphological properties. The focus of this review is on current advances in the characterisation and control of filamentous morphology with a separation of eukaryotic and prokaryotic systems. Furthermore, recent strategies to tailor the morphology through classical biochemical process parameters, morphology and genetic engineering to optimise the productivity of these filamentous systems are discussed.

Hydrodynamics, Fungal Physiology, and Morphology

Filamentous cultures, such as fungi and actinomycetes, contribute substantially to the pharmaceutical industry and to enzyme production, with an annual market of about 6 billion dollars. In mechanically stirred reactors, most frequently used in fermentation industry, microbial growth and metabolite productivity depend on complex interactions between hydrodynamics, oxygen transfer, and mycelial morphology. The dissipation of energy through mechanically stirring devices, either flasks or tanks, impacts both microbial growth through shearing forces on the cells and the transfer of mass and energy, improving the contact between phases (i.e., air bubbles and microorganisms) but also causing damage to the cells at high energy dissipation rates. Mechanical-induced signaling in the cells triggers the molecular responses to shear stress; however, the complete mechanism is not known. Volumetric power input and, more importantly, the energy dissipation/circulation function are the main parameters determining mycelial size, a phenomenon that can be explained by the interaction of mycelial aggregates and Kolmogorov eddies. The use of microparticles in fungal cultures is also a strategy to increase process productivity and reproducibility by controlling fungal morphology. In order to rigorously study the effects of hydrodynamics on the physiology of fungal microorganisms, it is necessary to rule out the possible associated effects of dissolved oxygen, something which has been reported scarcely. At the other hand, the processes of phase dispersion (including the suspended solid that is the filamentous biomass) are crucial in order to get an integral knowledge about biological and physicochemical interactions within the bioreactor. Digital image analysis is a powerful tool for getting relevant information in order to establish the mechanisms of mass transfer as well as to evaluate the viability of the mycelia. This review focuses on (a) the main characteristics of the two most common morphologies exhibited by filamentous microorganisms; (b) how hydrodynamic conditions affect morphology and physiology in filamentous cultures; and (c) techniques using digital image analysis to characterize the viability of filamentous microorganisms and mass transfer in multiphase dispersions. Representative case studies of fungi (Trichoderma harzianum and Pleurotus ostreatus) exhibiting different typical morphologies (disperse mycelia and pellets) are discussed.