Universidad de Malaga, Malaga, Spain.
Mol Plant Microbe Interact. 2011 Dec;24(12):1540-52. doi: 10.1094/MPMI-06-11-0162.
The antibacterial potential of four strains of Bacillus subtilis, UMAF6614, UMAF6619, UMAF6639, and UMAF8561, previously selected on the basis of their antifungal activity and efficacy against cucurbit powdery mildew, was examined. Among these strains, UMAF6614 and UMAF6639 showed the highest antibacterial activity in vitro, especially against Xanthomonas campestris pv. cucurbitae and Pectobacterium carotovorum subsp. carotovorum. These strains produced the three families of lipopeptide antibiotics known in Bacillus spp.: surfactins, iturins, and fengycins. Using thin-layer chromatography analysis and direct bioautography, the antibacterial activity could be associated with iturin lipopeptides. This result was confirmed by mutagenesis analysis using lipopeptide-defective mutants. The antibacterial activity was practically abolished in iturin-deficient mutants, whereas the fengycin mutants retained certain inhibitory capabilities. Analyses by fluorescence and transmission electron microscopy revealed the cytotoxic effect of these compounds at the bacterial plasma membrane level. Finally, biological control assays on detached melon leaves demonstrated the ability of UMAF6614 and UMAF6639 to suppress bacterial leaf spot and soft rot; accordingly, the biocontrol activity was practically abolished in mutants deficient in iturin biosynthesis. Taken together, our results highlight the potential of these B. subtilis strains as biocontrol agents against fungal and bacterial diseases of cucurbits and the versatility of iturins as antifungal and antibacterial compounds.
先前基于抗真菌活性和防治瓜类白粉病的功效而筛选出的 4 株枯草芽孢杆菌（Bacillus subtilis）菌株 UMAF6614、UMAF6619、UMAF6639 和 UMAF8561 的抗菌潜力得到了检验。在这些菌株中，UMAF6614 和 UMAF6639 表现出最高的体外抗菌活性，尤其对瓜类疫病病菌（Xanthomonas campestris pv. cucurbitae）和胡萝卜软腐欧文氏菌（Pectobacterium carotovorum subsp. carotovorum）具有较强的抑制作用。这些菌株产生了芽孢杆菌属已知的三种脂肽类抗生素：表面活性剂、伊枯草菌素和丰原素。通过薄层层析分析和直接生物自显影技术，可将抗菌活性与伊枯草菌素脂肽相关联。这一结果通过脂肽缺陷突变体的诱变分析得到了证实。在伊枯草菌素缺陷突变体中，抗菌活性几乎完全丧失，而丰原素突变体保留了一定的抑制能力。荧光和透射电子显微镜分析揭示了这些化合物在细菌质膜水平上的细胞毒性作用。最后，在离体瓜叶上进行的生物防治试验表明，UMAF6614 和 UMAF6639 能够抑制细菌性叶斑病和软腐病；因此，在缺乏伊枯草菌素生物合成的突变体中，生物防治活性几乎完全丧失。总之，我们的研究结果突出了这些枯草芽孢杆菌菌株作为防治瓜类真菌和细菌病害的生物防治剂的潜力，以及伊枯草菌素作为抗真菌和抗菌化合物的多功能性。
