Isolation and identification of flavonoid-producing endophytic fungi from medicinal plant Conyza blinii H.Lev that exhibit higher antioxidant and antibacterial activities

Background. Conyza blinii H. Lev is a medicinal plant that has a variety of pharmacological activities, but its study is at a standstill due to the shortage of resources. Method. This study utilized the surface sterilization method to isolate endophytic fungi, and they were preliminarily identified by morphology. Flavonoid-producing strains were screened by NaNO2-Al(NO)(3) colorimetry and further identified by the ITS sequence. Additionally, we used five antioxidant assays (DPPH, Hydroxyl radical, ABTS, FRAP and T-AOC assays) to systematically evaluate the antioxidant capacity of total flavonoids, and we also determined their antibacterial activity. Results. In this study, 21 endophytic fungi were isolated from wild Conyza blinii H. Lev for the first time. There were six flavonoid-producing strains, especially CBL11, whose total flavonoid content reached 50.78 +/- 2.4 mg/L. CBL12, CBL12-2 and CBL1-1 all exhibited excellent antioxidant activity. The effect of CBL12 was similar to that of ascorbic acid at low concentrations, and its radical scavenging rates for DPPH and ABTS were 94.56 +/- 0.29 % and 99.88 +/- 0.27%, respectively, while its IC50 values were only 0.11 +/- 0.01 mg/mL and 0.2 +/- 0.01 mg/mL. Through LC-MS, we found that CBL12 could produce many high-value flavonoids, such as 3-methoxyflavone, nobiletin, formononetin, scopoletin, and daidzein. Additionally, CBL9 had good antibacterial activity against both gram-positive and gram-negative bacteria. Notably, we obtained the high-yield strains CBL12 and CBL9, which not only had high yields (10.64 +/- 1.01 mg/L and 10.17 +/- 0.11 mg/L, respectively) but also had excellent biological activity. Hence, the results of this study provide new ideas for endophytic fungi that can be exploited as a source of flavonoids and other medicinal components from Conyza blinii H. Lev. Moreover, this study can serve as a reference for the development of rare medicinal materials.