Table_5_Bt GS57 Interaction With Gut Microbiota Accelerates Spodoptera exigua Mortality.XLS

The Beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae, Spodoptera) is an important global polyphagous pest. Pathogen infection could destroy the intestinal microbial homeostasis of insects, leading to the death of the host. However, the effect of the host intestinal microbial community on the insecticidal effect of Bacillus thuringiensis is rarely studied. In this study, the genome characteristics of Bt GS57 and the diversity and functions of the gut bacteria in S. exigua are investigated using crystal morphology, biological activity, and Illumina HiSeq high-throughput sequencing. The total size of the Bt GS57 genome is 6.17 Mbp with an average G + C content of 35.66%. Furthermore, the Bt GS57 genome contains six cry genes: cry1Ca, cry1Da, cry2Ab, cry9Ea, cry1Ia, and cry1Aa, and a vegetative insecticidal protein gene vip3Aa. The Bt GS57 strain can produce biconical crystals, mainly expressing 70 kDa and 130 kDa crystal proteins. The LC50 value of the Bt GS57 strain against the S. exigua larvae was 0.339 mg mL–1. Physiological and biochemical reactions showed that Bt GS57 belongs to B.t. var. thuringiensis. In addition, we found that B. thuringiensis can cause a dynamic change in the gut microbiota of S. exigua, with a significant reduction in bacterial diversity and a substantial increase in bacterial load. In turn, loss of gut microbiota significantly decreased the B. thuringiensis susceptibility of S. exigua larvae. Our findings reveal the vital contribution of the gut microbiota in B. thuringiensis-killing activity, providing new insights into the mechanisms of B. thuringiensis pathogenesis in insects.

甜菜夜蛾（Spodoptera exigua，鳞翅目：夜蛾科，灰翅夜蛾属）是一种全球性重要多食性害虫。病原菌侵染可破坏昆虫肠道微生物稳态，进而导致宿主死亡。然而，宿主肠道微生物群落对苏云金杆菌（Bacillus thuringiensis, Bt）杀虫活性的影响却鲜有研究。本研究通过晶体形态观察、生物活性测定及Illumina HiSeq高通量测序技术，解析了Bt GS57的基因组特征，以及甜菜夜蛾肠道细菌的多样性与功能。Bt GS57的基因组总大小为6.17 Mbp，G+C平均含量为35.66%。此外，该基因组包含6个杀虫晶体蛋白（cry）基因：cry1Ca、cry1Da、cry2Ab、cry9Ea、cry1Ia及cry1Aa，以及1个营养期杀虫蛋白基因vip3Aa。Bt GS57菌株可产生双锥形晶体，主要表达70 kDa与130 kDa的晶体蛋白。该菌株对甜菜夜蛾幼虫的半数致死浓度（LC50）为0.339 mg·mL–1。生理生化反应结果表明，Bt GS57属于苏云金杆菌苏云金变种（B.t. var. thuringiensis）。另外，研究发现苏云金杆菌可引发甜菜夜蛾肠道菌群的动态变化，具体表现为细菌多样性显著降低，而细菌载量大幅提升。反过来，肠道菌群的缺失会显著降低甜菜夜蛾幼虫对苏云金杆菌的易感性。本研究结果揭示了肠道菌群在苏云金杆菌杀虫活性中的关键作用，为阐明昆虫体内苏云金杆菌的致病机制提供了新视角。