Optimizing the degradation of aflatoxin B1 in corn by Trametes versicolor and improving the nutritional composition of corn.

BACKGROUND: Corn, being an important grain, is prone to contamination by aflatoxin B1 (AFB1 ), and AFB1 -contaminated corn severely endangers the health of humans and livestock. Trametes versicolor, a fungus that can grow in corn, possesses the ability to directly degrade AFB1 through its laccase. This study aimed to optimize the fermentation conditions for T. versicolor to degrade AFB1 in corn and investigate the effect of T. versicolor fermentation on the nutritional composition of corn. AFB1 -contaminated corn was used as the culture substrate for T. versicolor. A combination of single-factor experiments and response surface methodology was employed to identify the optimal conditions of AFB1 degradation. RESULTS: The optimal conditions of AFB1 degradation were as follows: 9 days of fermentation, a fermentation temperature of 26.7 °C, a moisture content of 70.5% and an inoculation amount of 4.9 mL (containing 51.99 mg of T. versicolor mycelia). With the optimal conditions, the degradation rate of AFB1 in corn could reach 93.01%, and the dry basis content of protein and dietary fiber in the fermented corn was significantly increased. More importantly, the lysine content in the fermented corn was also significantly increased. CONCLUSION: This is the first report that direct fermentation of AFB1 -contaminated corn by T. versicolor not only efficiently degrades AFB1 but also improves the nutritional composition of corn. These findings suggest that the fermentation of corn by T. versicolor is a promising, environmentally friendly and efficient approach to degrade AFB1 and improve the nutritional value of corn. © 2023 Society of Chemical Industry.

Edible fungi efficiently degrade aflatoxin B1 in cereals and improve their nutritional composition by solid-state fermentation.

Aflatoxin B1 (AFB1) is extremely harmful to human and livestock. Laccase, a green catalyst, has been shown to effectively degrade AFB1 and can be obtained from edible fungi. The objective of this study was to screen edible fungi with high laccase activity and determine their effects on the degradation of AFB1 in cereals and the nutritional composition of the cereals through solid-state fermentation. Results from plate assays confirmed that 51 of the 55 tested edible fungi could secrete laccase. Submerged fermentation results showed that 17 of the 51 edible fungi had maximum laccase activity exceeding 100 U/L. The growth of different edible fungi varied significantly in corn, rice and wheat. More importantly, 6 edible fungi with high laccase activity and good growth could efficiently degrade AFB1 in cereals. We found for the first time that Ganoderma sinense could not only secrete highly active laccase and efficiently degrade AFB1 in corn by 92.91%, but also improve the nutritional quality of corn. These findings reveal that solid-state fermentation of cereals with edible fungi is an environmentally friendly and efficient approach for degrading AFB1 in cereals and improving the nutritional composition of cereals.

Cmfhp Gene Mediates Fruiting Body Development and Carotenoid Production in Cordyceps militaris.

Cordyceps militaris fruiting bodies contain a variety of bioactive components that are beneficial to the human body. However, the low yield of fruiting bodies and the low carotenoid content in C. militaris have seriously hindered the development of the C. militaris industry. To elucidate the developmental mechanism of the fruiting bodies of C. militaris and the biosynthesis mechanism of carotenoids, the function of the flavohemoprotein-like Cmfhp gene of C. militaris was identified for the first time. The Cmfhp gene was knocked out by the split-marker method, and the targeted gene deletion mutant ΔCmfhp was obtained. An increased nitric oxide (NO) content, no fruiting body production, decreased carotenoid content, and reduced conidial production were found in the mutant ΔCmfhp. These characteristics were restored when the Cmfhp gene expression cassette was complemented into the ΔCmfhp strain by the Agrobacterium tumefaciens-mediated transformation method. Nonetheless, the Cmfhp gene had no significant effect on the mycelial growth rate of C. militaris. These results indicated that the Cmfhp gene regulated the biosynthesis of NO and carotenoids, the development of fruiting bodies, and the formation of conidia. These findings potentially pave the way to reveal the developmental mechanism of fruiting bodies and the biosynthesis mechanism of carotenoids in C. militaris.

Transcriptome Analysis of Cordyceps militaris Reveals Genes Associated With Carotenoid Synthesis and Identification of the Function of the Cmtns Gene.

Cordyceps militaris, a valuable edible and medicinal fungus, has attracted increasing attention because of its various bioactive ingredients. However, the biosynthetic pathway of C. militaris carotenoids is still unknown due to lack of transcriptome information. To uncover genes related to the biosynthesis of C. militaris carotenoids, the transcriptomes of mycelia CM10_D cultured under dark conditions and mycelia CM10_L cultured under light exposure conditions were sequenced. Compared with mycelia CM10_D, 866 up-regulated genes and 856 down-regulated genes were found in mycelia CM10_L. Gene ontology (GO) analysis of differentially expressed genes (DEGs) indicated that DEGs were mainly classified into the "metabolic process," "membrane," and "catalytic activity" terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of DEGs suggested that DEGs were mainly enriched in "metabolic pathways," "MAPK signaling pathway-yeast," and "biosynthesis of secondary metabolites." In addition, the carotenoid content of the Cmtns gene deletion mutant (ΔCmtns) was significantly lower than that of the wild-type C. militaris CM10, while the carotenoid content of the complementary strain (ΔCmtns-c) of the Cmtns gene was not significantly different from that of C. militaris CM10, suggesting that the Cmtns gene significantly affected the biosynthesis of carotenoids in C. militaris. These results potentially pave the way for revealing the biosynthetic pathway of carotenoids and improving carotenoids production in C. militaris.

Purification and structural characterization of a novel natural pigment: cordycepene from edible and medicinal mushroom Cordyceps militaris.

In the present work, a novel cordycepic pigment was successfully isolated and identified from Cordyceps militaris, as well as named as cordycepene (C14H17N1O4), according to the long unsaturated conjugated polyene structural characteristic. Cordycepene is sensitive to light, high temperature (≥ 60 °C), and acidic condition (pH ≤ 3), but possesses high stability against metal ions, and under alkaline and neutral conditions. Cordycepene shows a comparable DPPH (1,1-diphenyl-2-picrylhydrazyl) radical-scavenging activity at higher concentration (≥ 2 mg/mL) to vitamin C. Cordycepene promotes the growth of HSF (human skin fibroblast cell) after incubation for 72 h, and has an ability to repair the UV light-treated HSF cells. In addition, cordycepene increases the antioxidant activity (SOD, superoxide dismutase; GSH-Px, glutathione peroxidase; CAT, catalase) and decreases MDA (malondialdehyde) level, indicating that cordycepene inhibits the photochemical senescence of HSF by enhancing the antioxidant defense system. The discovery of cordycepene can provide a basis for research on light incubation and the accumulation of yellow pigment (carotenoids) from C. militaris.

Advances in research on Cordyceps militaris degeneration.

As a highly valued fungus, Cordyceps militaris has been widely used all over the world. Although the wild resources of C. militaris are limited, the fruiting bodies of C. militaris have been successfully cultivated on a large-scale. However, the high-frequency degeneration of C. militaris during subculture and preservation seriously limits the development of the C. militaris industry. How to solve the degeneration of C. militaris has become an unsolved bottleneck problem throughout the whole Cordyceps industry. The aim of this review is to illustrate the phenotypic changes after the degeneration of C. militaris, focusing on the causes (including environmental factors and genetic variation) of C. militaris degeneration. Moreover, genetic variation is the root cause of the degeneration of C. militaris strains. Measures to prevent the degeneration of C. militaris are also discussed in this review. This paper will increase understanding of the degeneration mechanism of C. militaris, provide a reference for solving the degeneration problem of C. militaris, and lay a foundation for promoting the sustainable development of C. militaris.

Optimization of Cultivation Conditions of Lingzhi or Reishi Medicinal Mushroom, Ganoderma lucidum (Agaricomycetes) for the Highest Antioxidant Activity and Antioxidant Content.

Ganoderma lucidum is a famous medicinal mushroom that is rich in antioxidants. The content of antioxidant components of grains can be effectively improved by G. lucidum as the fermenting strain. Optimization of the solid-state fermentation medium and optimization of the fermentation conditions were studied. The optimal fermentation substrate combination of G. lucidum TS (GL-TS) was 46.79% buckwheat, 53.21% rice; the optimal fermentation substrate combination of G. lucidum Am (GL-Am) was 4.17% soybean, 95.83% rice. The optimal fermentation conditions of GL-TS and GL-Am were as follows: inoculum amounts of 4.5% and 7.5%, temperatures of 30°C and 32°C, medium moisture content of 70% for both media, material granularities of 0.212-0.355 mm and 0.500-0.710 mm, and optimal fermentation time of 12.0 d and 10.5 d, respectively. Results of the analysis of antioxidant components in the fermentation substrates indicated that the antioxidant components were rich in antioxidant varieties and high in content. The contents of the antioxidant components (triterpenoids, total polyphenols, reducing sugars, anthocyanins, superoxide dismutase, glutathione, vitamin C, and vitamin E) in the full-fermentation substrates were greater than those in the nonfennentation substrates (except for flavonoids in the full-fermentation substrates, which were less than in the nonfennentation substrates). Glutathione was the major antioxidant component in the fermentation substrates, and the glutathione content was the highest. Therefore, the fermentation substrates of G. lucidum can be used to make antioxidant foods. This research contributes to the foundation for developing antioxidant foods based on G. lucidum.

Targeted Gene Deletion in Cordyceps militaris Using the Split-Marker Approach.

The macrofungus Cordyceps militaris contains many kinds of bioactive ingredients that are regulated by functional genes, but the functions of many genes in C. militaris are still unknown. In this study, to improve the frequency of homologous integration, a genetic transformation system based on a split-marker approach was developed for the first time in C. militaris to knock out a gene encoding a terpenoid synthase (Tns). The linear and split-marker deletion cassettes were constructed and introduced into C. militaris protoplasts by PEG-mediated transformation. The transformation of split-marker fragments resulted in a higher efficiency of targeted gene disruption than the transformation of linear deletion cassettes did. The color phenotype of the Tns gene deletion mutants was different from that of wild-type C. militaris. Moreover, a PEG-mediated protoplast transformation system was established, and stable genetic transformants were obtained. This method of targeted gene deletion represents an important tool for investigating the role of C. militaris genes.