Ultrasonic-assisted extraction and light-dependent antimicrobial activities of thiophenes from Tagetes erecta

Marigold ( Tagetes species) is rich in thiophenes and efficient extraction of thiophenes is vital for their activity evaluation and utilization. In this study, ultrasonic-assisted extraction (UAE) was used to extract thiophenes from Tagetes erecta and the extraction conditions were further optimized by orthogonal experiment. The results revealed the optimal extraction condition was solid-liquid ratio (g/mL) 1:20, ultrasonic duration 50 min, and ultrasonic temperature 55 °C. Thiophenes were biosynthesized in the root tissues of three marigolds 'Juwang', 'Taishan' and 'Discovery', and the root extract of 'Juwang' at stage V (J-O-V) had the highest a-terthienyl (α-T) content of 1.809 mg/g DW. Furthermore, the inhibitory effects of root extract J‑O‑V and synthetic α-T on P. expansum , Gram‑positive bacteria ( S. epidermidis , L. monocytogenes , B. subtilis ), and Gram‑negative bacteria ( E. coli , P. syringae pv. tomato , P. syringae pv. actinidiae ) were evaluated using disk diffusion, microbroth dilution or agar dilution assays. The results demonstrated the UVA-dependent antimicrobial activity against fungi and Gram-positive bacteria, whereas weaker phototoxicity for Gram-negative bacteria. Notably, marigold root extract exhibited superior inhibitory effects over synthetic α-T at equivalent concentrations, which can be attributed to the additional thiophene derivatives (BBT, BBTOH, BBTOAc) identified by HPLC-Q-TOF/MS analysis. Additionally, all the extracts from roots of 'Juwang', 'Taishan' and 'Discovery' at stage V confirmed their marked inhibition of P. expansum on wounding inoculated tomatoes, which exhibited a dose-dependent suppression in terms of α-T, indicating the potential application of naturally obtained thiophenes in postharvest preservation. Taken together, UAE-based marigold ( Tagetes erecta ) root extraction yields plant-derived photosensitive thiophenes with high antibacterial activity to unlock promising utilizations across diverse industrial scenarios.