Pleurotus ostreatus is one of the widely cultivated edible fungi across the world. Mycelial subculture is an indispensable part in the process of cultivation and production for all kinds of edible fungi. However, successive subcultures usually lead to strain degeneration. The degenerated strains usually have a decrease in stress resistance, yield, and an alteration in fruiting time, which will subsequently result in tremendous economic loss. Through proteomic analysis, we identified the differentially expressed proteins (DEPs) in the mycelium of Pleurotus ostreatus from different subcultured generations. We found that the DNA damage repair system, especially the double-strand breaks (DSBs), repairs via homologous recombination, was impaired in the subcultured mycelium, and gradual accumulation of the DSBs would lead to the strain degeneration after successive subculture. The TUNEL assay further confirmed our finding about the DNA breaks in the subcultured mycelium. Interestingly, the enzyme activity of laccase, carboxylic ester hydrolase, α-galactosidase, and catalase directly related to passage number could be used as the characteristic index for strain degeneration determination. Our results not only reveal for the first time at the molecular level that genomic instability is the cause of degeneration, but also provide an applicable approach for monitoring strain degeneration in process of edible fungi cultivation and production.
Trichoderma strain T-33 has been demonstrated to have inhibitory effect on the fungus species Cytospora chrysosperma. Here, an active antifungal compound was obtained from Trichoderma strain T-33 extract via combined separation technologies, including organic solvent extraction, liquid chromatography, and thin-layer chromatography. The purified compound was further characterized by advanced analytical technologies to elucidate its chemical structure. Results indicated that the active antifungal compound in Trichoderma strain T-33 extract is 2,5- cyclohexadiene-1,4-dione-2,6-bis (1,1-dimethylethyl).
Polyphenol oxidase (PPO) plays a key role in tea processing. It catalyzes the conversion of tea polyphenols into theaflavin and its derivatives. PPO was partially purified and characterized in both its soluble form (sPPO) and membrane-bound form (mPPO) from tea (Camellia sinensis) leaves. Both forms were purified by three-phase partitioning and membrane ultrafiltration. sPPO and mPPO showed high activity against diphenols as substrate and had the highest affinity for catechol and caffeic acid. The optimum temperatures and pH for enzyme activity were different. mPPO was more stable than sPPO in the acidic pH range. Among the chemical inhibitors studied, oxalic acid exerted the highest inhibitory effect on mPPO, whereas EDTA showed the highest inhibitory effect on sPPO. Both sPPO and mPPO showed similar enzymatic synthesis rates in the formation of theaflavin-3'-gallate and theaflavin-3,3'-gallate. At high concentrations of the substrate, the synthesis of theaflavins was inhibited due to the presence of high levels of ester catechins. However, mPPO showed stronger stability against inhibition by ester catechins than sPPO.
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