Cotton waste, a growth medium for Volvariella volvacea, has significant commercial and nutritional value. Under controlled environmental conditions, substrate nutrient composition and microorganisms affect the growth of V. volvacea. In this study, the changes in the nutrient content of the substrate at different stages of fruiting body development were compared based on an 86% waste cotton substrate, and microbial diversity was studied via 16S rRNA analysis. The results indicated that there were significant differences in nutrient content in the substrate at different stages of fruiting body development. The total contents of carbon, nitrogen, and phosphorus initially increased but then decreased due to nutrient absorption and utilization by V. volvacea. It was also found that large amounts of organic nitrogen decomposed into more readily utilizable inorganic nitrogen. The nutritional content and microbial community structure of the substrate during the egg stage significantly differed from those during the other four stages, making the egg stage the most critical period in cultivation. Through correlation analysis between nutrient content and microbial differences, it was found that differential microbial taxa (Beijerinckiaceae, Burkholderiales, Chitinophaga jiangningensis, etc.) with nitrogen fixation, denitrification, and cellulose decomposition functions were significantly related to carbon- and nitrogen-related indicators such as nitrate nitrogen, microbial biomass carbon, and alkali-hydrolyzed nitrogen. These microorganisms play important roles in determining the variation in the nutritional profile of the substrate. This study provides a theoretical basis for promoting the absorption and utilization of nutrients by V. volvacea by altering the structure of the microbial community of the growth substrate.

A novel protease was isolated from the fruiting bodies of the straw mushroom Volvariella volvacea. The protease was purified 13.48-fold using a series of techniques, including ammonium sulfate precipitation, ultrafiltration, diethylaminoethyl fast-flow (DEAE FF) ion-exchange chromatography, and Superdex 75 gel filtration chromatography, resulting in a specific enzyme activity of 286.82 U/mg toward casein as a substrate. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed that the purified protease had a molecular weight of 24 kDa. The enzyme exhibited optimal activity at pH 7 and 50 °C, showing sensitivity to alkaline conditions and instability at elevated temperatures. The presence of Ca²⁺ significantly enhanced enzyme activity, whereas Ni²⁺ and Cu²⁺ exerted strong inhibitory effects, with other metal ions showing weak inhibition. β-mercaptoethanol, Tween-80, and Triton X-100 had more pronounced inhibitory effects, whereas PMSF, EDTA, and CTAB had weaker inhibitory effects. The Michaelis constant (Km) and maximum velocity (Vm) of the protease were determined to be 1.34 g/L and 3.45 μg/(mL·min), respectively. The protease exhibited a greater degree of enzymatic degradation of soybean-isolate protein (7.58%) compared to trypsin (5.24%), with the enzyme product containing a high percentage of medicinal amino acids (73.54%), particularly phenylalanine (Phe) and arginine (Arg), suggesting their presence at the enzyme’s active site. These findings suggest that the protease from V. volvacea holds promising potential for applications in the food industry, particularly in protein hydrolysate production and flavor enhancement.

Agaricus subrufescens Peck is a nutrient-rich edible fungi with a distinctive flavor, but most varieties are sensitive to cadmium (Cd), making cadmium contamination common during cultivation. Currently, excessive fertilizer uses and increased solid waste are exacerbating cadmium contamination in soils. Since A. subrufescens utilize agricultural residues like straw and livestock manure as cultivation substrates, Cd can be adsorbed readily, leading to secondary accumulation. In this study, the toxic effects of and response mechanisms to different Cd concentrations with respect to mycelial growth, heavy metal accumulation, and antioxidant systems of A. subrufescens were systematically investigated. The results indicated that the mycelia exhibited Cd accumulation capacity, with accumulation levels positively correlated with stress concentration. At a Cd concentration of 5 mg/L, the intracellular Cd concentration in the mycelia reached approximately 800 mg/kg. As the Cd concentration increased, the efficiency of Cd uptake by mycelia correspondingly decreased. Cadmium stress (≥0.5 mg/L) significantly inhibited mycelial growth and induced morphological abnormalities, with the mycelia exhibiting yellowing. Furthermore, Cd induced dose-dependent oxidative stress. Hydrogen peroxide and MDA levels peaked at a Cd concentration of 2 mg/L, reaching 2.26 μmol/g and 8.98 nmol/g, respectively, indicating heightened lipid peroxidation. Low concentrations of Cd (≤2 mg/L) promoted increases in ASA and GSH activity. SOD, POD, GR, and APX activities significantly increased, with the ASA-GSH cycle synergistically scavenging ROS. CAT activity remained persistently inhibited, APX/GR activity was suppressed, and total sugar metabolism was disrupted, leading to the collapse of antioxidant defenses. In summary, depending on the Cd concentration, A. subrufescens mycelia exhibit markedly different responses at low versus high concentrations. This study provides a foundation for further research into the application of edible fungi in heavy metal-resistant cultivation.

Although the aroma profile of Lentinula edodes has been extensively studied in fruiting bodies, the mycelial stage provides a distinct context for elucidating the fundamental metabolic pathways, free from the complexities of organismal development. To elucidate the mechanism underlying aroma differences between L. edodes strain 808 (the control strain) and its mutant strain ww808 (with almost no shiitake aroma), this study employed GC-IMS combined with PCA and OPLS-DA to identify key aroma biomarkers during the mycelial stage. All analyses were performed with three biological replicates. Furthermore, fatty acids composition, key enzyme activities of the LOX pathway, and their gene expression levels were systematically compared. The results indicated significant differences in the content of volatile aroma compounds in the mycelia of the two strains, primarily stemming from fundamental restructuring of gene expression and enzyme activity in the LOX pathway. The LOX gene expression and LOX activity of 808 mycelium were relatively high, facilitating the accumulation of key aroma compounds such as phenylethanal, benzaldehyde, and ethyl acetate, which constitute its distinctive aromatic profile. However, although the mycelium of ww808 possessed richer fatty acid precursor (C18:2), its lower LOX gene expression restricted the flux of this pathway. The significantly increased expression of ADH2, ADH3, and ADH5 genes and higher ADH activity enhanced the conversion capacity of aldehydes to alcohols and ketones. Given the generally higher odor thresholds of alcohols and ketones compared to aldehydes, distinct aroma profiles emerged between the two strains. Pearson correlation analysis further confirmed the significant correlations between the aroma biomarkers, fatty acids, key genes, and enzyme activities. This study revealed the formation mechanism of aroma differences in the mycelia of the two strains from the perspective of metabolic pathways, providing a theoretical foundation and candidate targets for the directed genetic improvement of L. edodes aroma quality.

The addition of nutritional additives to the cultivation substrate is an effective way to increase edible fungus yields; however, the mechanisms by which these additives regulate the structure and function of the substrate microbial community to promote nutrient transformation remain unclear. In this study, a patented composite additive composed of soybean meal, corn protein, and wheat bran was added to a Volvariella volvacea cultivation system based on spent Pleurotus eryngii substrate after secondary fermentation, and the additive-treated (T) and control (ck) groups were compared across different cultivation stages. The additive increased V. volvacea yield by 26.4% (4.02 vs. 3.18 kg/m²) and increased fruiting body amino acid content by 16.43%, in addition to shifting carbon and nitrogen metabolism toward amino acid accumulation and biomass. Throughout cultivation, the additive sustained higher cellulase (CL) and alkaline protease (AKP) activities, increased cellulose degradation and organic nitrogen mineralization, and enlarged the pool of available carbon and nitrogen in the substrate. Co-abundance group (CAG) network analysis of 626 ASVs (577 bacterial and 49 fungal ASVs) revealed that the additive was associated with three potential bacterial–fungal functional modules in a stage-specific manner: a cellulose-degrading and nitrogen-accumulating module, a carbon-assimilating module, and a nitrogen-mineralizing module. The core taxa potentially associated with carbon and nitrogen transformation included the bacteria Pseudoxanthomonas and Thermopolyspora and the fungus Mycothermus, together with the additive-enriched genera Schlegelella, Niabella, and Chelatococcus. ASV-level resolution further revealed an intragenus functional division of Mycothermus, in which two ASV clusters were associated with cellulose degradation and nitrogen mineralization. These findings elucidate the mechanism whereby additives enrich functional microbial guilds, accelerate coupled carbon–nitrogen turnover, and ultimately increase the yield and quality of V. volvacea, providing a theoretical basis for the precise management of spent-substrate-based edible fungus cultivation.