Rational Optimization of 1,2,3-Triazole-Tailored Carbazoles As Prospective Antibacterial Alternatives with Significant In Vivo Control Efficiency and Unique Mode of Action

Abstract

Plant bacterial diseases can potentially damage agricultural products around the world, and few effective bactericides can manage these infections. Herein, to sequentially explore highly effective antibacterial alternatives, 1,2,3-triazole-tailored carbazoles were rationally fabricated. These compounds could suppress the growth of three main intractable pathogens including Xanthomonas oryzae pv oryzae (Xoo), X. axonopodis pv citri (Xac), and Pseudomonas syringae pv actinidiae (Psa) with lower EC₅₀ values of 3.36 (3p), 2.87 (3p), and 4.57 μg/mL (3r), respectively. Pot experiments revealed that compound 3p could control the rice bacterial blight with protective and curative efficiencies of 53.23% and 50.78% at 200 μg/mL, respectively. Interestingly, the addition of 0.1% auxiliaries such as organic silicon and orange oil could significantly enhance the surface wettability of compound 3p toward rice leaves, resulting in improved control effectiveness of 65.50% and 61.38%, respectively. Meanwhile, compound 3r could clearly reduce the white pyogenic exudates triggered by Psa infection and afforded excellent control efficiencies of 79.42% (protective activity) and 78.74% (curative activity) at 200 μg/mL, which were quite better than those of commercial pesticide thiodiazole copper. Additionally, a plausible apoptosis mechanism for the antibacterial behavior of target compounds was proposed by flow cytometry, reactive oxygen species detection, and defensive enzyme (e.g., catalase and superoxide dismutase) activity assays. The current work can promote the development of 1,2,3-triazole-tailored carbazoles as prospective antibacterial alternatives bearing an intriguing mode of action.

Keywords: 1,2,3-triazole; antibacterial activity; apoptosis mechanism; carbazoles; enzyme activity.