Isolation and identification of flavonoid-producing endophytic fungi from medicinal plant Conyza blinii H.Lév 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.