Abstract：
The present study investigated the antibacterial mechanism, control efficiency, and nontarget toxicity of actinomycin X2 (Act-X2) against Xanthomonas citri subsp. citri (Xcc) for the first time. Act-X2 almost completely inhibited the proliferation of Xcc in the growth curve assay at a concentration of 0.25 MIC (minimum inhibitory concentration, MIC = 31.25 μg/mL). This inhibitory effect was achieved by increasing the production of reactive oxygen species (ROS), blocking the formation of biofilms, obstructing the synthesis of intracellular proteins, and decreasing the enzymatic activities of malate dehydrogenase (MDH) and succinate dehydrogenase (SDH) of Xcc. Molecular docking and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) analysis results indicated that Act-X2 steadily bonded to the RNA polymerase, ribosome, malate dehydrogenase, and succinate dehydrogenase to inhibit their activities, thus drastically reducing the expression levels of related genes. Act-X2 showed far more effectiveness than the commercially available pesticide Cu2(OH)3Cl in the prevention and therapy of citrus canker disease. Furthermore, the nontarget toxicity evaluation demonstrated that Act-X2 was not phytotoxic to citrus trees and exhibited minimal toxicity to earthworms in both contact and soil toxic assays. This study suggests that Act-X2 has the potential as an effective and environmentally friendly antibacterial agent.
摘要：
本研究探讨了抗菌机制，控制效率,放线菌素X2（Act-X2）对柑橘黄单胞菌亚种的非目标毒性。citri(Xcc)第一次。在0.25MIC的浓度下，Act-X2几乎完全抑制了Xcc在生长曲线测定中的增殖（最小抑制浓度，MIC=31.25μg/mL)。这种抑制作用是通过增加活性氧（ROS）的产生来实现的，阻止生物膜的形成，阻碍细胞内蛋白质的合成，并降低Xcc的苹果酸脱氢酶（MDH）和琥珀酸脱氢酶（SDH）的酶活性。分子对接和定量逆转录酶聚合酶链反应(qRT-PCR)分析结果表明,Act-X2与RNA聚合酶稳定结合,核糖体,苹果酸脱氢酶，和琥珀酸脱氢酶来抑制它们的活性，从而大大降低了相关基因的表达水平。在预防和治疗柑橘溃疡病方面，Act-X2比市售农药Cu2（OH）3Cl表现出更高的效力。此外，非目标毒性评估表明，Act-X2对柑橘树没有植物毒性，并且在接触和土壤毒性测定中对蚯蚓的毒性最小。这项研究表明，Act-X2具有作为一种有效和环保的抗菌剂的潜力。
