Bt GS57 Interaction With Gut Microbiota Accelerates Spodoptera exigua Mortality

Yazi Li; Dan Zhao; Han Wu; Yujie Ji; Zhaorui Liu; Xiaochang Guo; Wei Guo; Yang Bi

doi:10.3389/fmicb.2022.835227

Bt GS57 Interaction With Gut Microbiota Accelerates Spodoptera exigua Mortality

Front Microbiol. 2022 Mar 23:13:835227. doi: 10.3389/fmicb.2022.835227. eCollection 2022.

Authors

Yazi Li¹, Dan Zhao¹, Han Wu¹, Yujie Ji², Zhaorui Liu¹, Xiaochang Guo¹, Wei Guo^{1

2}, Yang Bi³

Affiliations

¹ College of Plant Protection, Hebei Agricultural University, Baoding, China.
² Graduate School of Chinese Academy of Agricultural Sciences, Beijing, China.
³ College of Bioscience and Resources Environment, Beijing University of Agriculture, Beijing, China.

Abstract

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.

Keywords: Bt GS57; Spodoptera exigua; diversity; dysbiosis; genomic feature; gut microbiota.