AUTHOR=Li Yazi , Zhao Dan , Wu Han , Ji Yujie , Liu Zhaorui , Guo Xiaochang , Guo Wei , Bi Yang 

TITLE=Bt GS57 Interaction With Gut Microbiota Accelerates Spodoptera exigua Mortality

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.835227

DOI=10.3389/fmicb.2022.835227

ISSN=1664-302X

ABSTRACT=<p>The Beet armyworm <italic>Spodoptera exigua</italic> (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 <italic>Bacillus thuringiensis</italic> is rarely studied. In this study, the genome characteristics of Bt GS57 and the diversity and functions of the gut bacteria in <italic>S. exigua</italic> 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 <italic>cry</italic> genes: <italic>cry1Ca</italic>, <italic>cry1Da</italic>, <italic>cry2Ab</italic>, <italic>cry9Ea</italic>, <italic>cry1Ia</italic>, and <italic>cry1Aa</italic>, and a vegetative insecticidal protein gene <italic>vip3Aa</italic>. The Bt GS57 strain can produce biconical crystals, mainly expressing 70 kDa and 130 kDa crystal proteins. The LC<sub>50</sub> value of the Bt GS57 strain against the <italic>S. exigua</italic> larvae was 0.339 mg mL<sup>–1</sup>. Physiological and biochemical reactions showed that Bt GS57 belongs to <italic>B.t.</italic> var. <italic>thuringiensis</italic>. In addition, we found that <italic>B. thuringiensis</italic> can cause a dynamic change in the gut microbiota of <italic>S. exigua</italic>, with a significant reduction in bacterial diversity and a substantial increase in bacterial load. In turn, loss of gut microbiota significantly decreased the <italic>B. thuringiensis</italic> susceptibility of <italic>S. exigua</italic> larvae. Our findings reveal the vital contribution of the gut microbiota in <italic>B. thuringiensis</italic>-killing activity, providing new insights into the mechanisms of <italic>B. thuringiensis</italic> pathogenesis in insects.</p>