Midgut microbiota and host immunocompetence underlie Bacillus thuringiensis killing mechanism
Midgut microbiota and host immunocompetence underlie Bacillus thuringiensis killing mechanism
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DOI：
10.1073/pnas.1521741113
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发表时间：
2016-08-23
影响因子：
11.1
通讯作者：
Pennacchio, Francesco
中科院分区：
文献类型：
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作者：
Caccia, Silvia;Di Lelio, Ilaria;Pennacchio, Francesco
苏云金芽孢杆菌是一种广泛使用的昆虫病原细菌，产生杀虫毒素，其中一些毒素在抗虫转基因作物中表达。令人惊讶的是，苏云金杆菌的杀灭机制仍然存在争议。特别是，宿主中肠微生物区系引起的败血症的重要性仍然存在争议，因为缺乏实验证据，而没有对中肠及其内容物进行剧烈的操作。在这里，这个关键问题是通过RNAi介导的对鳞翅目寄主斜纹夜蛾免疫基因的沉默来解决的，而中肠微生物区系保持不变。由此产生的细胞免疫抑制的特征是结瘤反应减少，这与苏云金杆菌和Cry毒素引起的寄主幼虫死亡率显著增加有关。这是由中肠细菌通过毒素诱导的上皮损伤进入体腔后不受控制的增殖所决定的。因此，经Cry1Ca毒素处理后，血淋巴微生物区系发生了显著变化，表现出明显的沙雷氏菌和梭状芽孢杆菌的优势，从无症状的肠道共生菌转变为血腔性病原菌。这些实验结果证明了寄主肠道菌群在苏云金芽孢杆菌杀灭活性中的重要贡献，并为开发新的害虫控制策略提供了良好的基础，旨在通过降低寄主的免疫活性来增强生防剂的影响。
Bacillus thuringiensis is a widely used bacterial entomopathogen producing insecticidal toxins, some of which are expressed in insect-resistant transgenic crops. Surprisingly, the killing mechanism of B. thuringiensis remains controversial. In particular, the importance of the septicemia induced by the host midgut microbiota is still debated as a result of the lack of experimental evidence obtained without drastic manipulation of the midgut and its content. Here this key issue is addressed by RNAi-mediated silencing of an immune gene in a lepidopteran host Spodoptera littoralis, leaving the midgut microbiota unaltered. The resulting cellular immunosuppression was characterized by a reduced nodulation response, which was associated with a significant enhancement of host larvae mortality triggered by B. thuringiensis and a Cry toxin. This was determined by an uncontrolled proliferation of midgut bacteria, after entering the body cavity through toxin-induced epithelial lesions. Consequently, the hemolymphatic microbiota dramatically changed upon treatment with Cry1Ca toxin, showing a remarkable predominance of Serratia and Clostridium species, which switched from asymptomatic gut symbionts to hemocoelic pathogens. These experimental results demonstrate the important contribution of host enteric flora in B. thuringiensis-killing activity and provide a sound foundation for developing new insect control strategies aimed at enhancing the impact of biocontrol agents by reducing the immunocompetence of the host.