Successive mycelial subculturing decreased lignocellulase activity and increased ROS accumulation in Volvariella volvacea

Abstract

Strain degradation is a common problem in many artificially-cultivated edible mushrooms. As a fungus with poor tolerance to low-temperature, Volvariella volvacea cannot delay its degradation by long-term low temperature storage like other fungi, so its degradation is particularly severe, which hinders industrial applications. Periodic mycelial subculture is a common storage method for V. volvacea, but excessive subculturing can also lead to strain degeneration. After 20 months of continuous subculturing every 3 days, V. volvacea strains S1–S20 were obtained, and their characteristics throughout the subculture process were analyzed. With increasing number of subculture, the growth rate, mycelial biomass, the number of fruiting bodies and biological efficiency gradually decreased while the production cycle and the time to primordium formation was lengthened. Strains S13–S20, obtained after 13–20 months of mycelial subculturing, also lacked the ability to produce fruiting bodies during cultivation experiments. Determination of reactive oxygen species (ROS) content as well as enzyme activity showed that decreased lignocellulase activity, along with excessive accumulation of ROS, was concomitant with the subculture-associated degeneration of V. volvacea. Reverse transcription polymerase chain reaction (RT-PCR) was eventually used to analyze the gene expression for lignocellulase and antioxidant enzymes in subcultured V. volvacea strains, with the results found to be consistent with prior observations regarding enzyme activities. These findings could form the basis of further studies on the degeneration mechanism of V. volvacea and other fungi.

A Review Delving into the Factors Influencing Mycelium-Based Green Composites (MBCs) Production and Their Properties for Long-Term Sustainability Targets

“…Fungal strain degeneration: Frequent strain degradation is a significant concern in fungal product production, particularly affecting economically important varieties like edible and medicinal mushrooms, resulting in substantial production losses. Although tip mycelium subculture is commonly used for vitality maintenance, successive subculturing can lead to strain degradation, affecting mycelium growth efficiency over time [ 174 ]. Continuous subculturing without reintroducing genetic diversity can cause a decline in vitality [ 175 , 176 ].…”

“…hough tip mycelium subculture is commonly used for vitality maintenance, successive subculturing can lead to strain degradation, affecting mycelium growth efficiency over time [174]. Continuous subculturing without reintroducing genetic diversity can cause a decline in vitality [175,176].…”

The phenomenon of strain degeneration in biotechnologically relevant fungi

“…Some of these phenomena are shortly introduced in the following section in order to differentiate the term for the rest of the review. Certain basidiomycetes are reported to lose their ability to produce fruiting bodies during cultivation (Magae et al 2005;Piscitelli et al 2005;Lee et al 2014;Chen et al 2019;Zhu et al 2020;Pérez et al 2021;Zhao et al 2022). Cordyceps militaris, for example, is commercially cultivated as a pharmaceutical and food resource and frequently degenerates through subculture and storage.…”

Effects of MAT1-2 Spore Ratios on Fruiting Body Formation and Degeneration in the Heterothallic Fungus Cordyceps militaris

“…Successive subculturing of mycelia or spores for several generations in filamentous fungi and mushrooms causes degeneration [12][13][14][15][16][17][18]. Strain degeneration in C. militaris is characterized by the reduction in fruiting body formation, mycelial growth rate, pigmentation, and production of bioactive metabolites [19,20].…”