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.