Characterization of a Bacterial Symbiont Asaia sp. in the White-Backed Planthopper, Sogatella furcifera, and Its Effects on Host Fitness.

Fei Li,Hongxia Hua,Maolin Hou,Asad Ali

doi:10.3389/fmicb.2019.02179

Abstract

The white-backed planthopper (WBPH), Sogatella furcifera Horváth (Hemiptera: Delphacidae), is an economically significant rice insect pest that harbors a primary fungal yeast-like symbiont (YLS), and some secondary bacterial symbionts like Wolbachia and Cardinium. In the present study, an additional bacterial symbiont in WBPH was characterized. Phylogenetic analysis employing the 16S rRNA gene showed a bacterium closely related to Asaia of Nilaparvata lugens and Nysius expressus, and Asaia krungthepensis. TEM observation of the bacterium showed the typical morphology of Asaia sp. with signature filamentous structures in the nucleoid region. These results indicate that the bacterium belongs to Asaia. The Asaia bacterium was detected in all the tested individual adults and tissues of the laboratory WBPH population but showed varying infection rates (ca 45%) in the field collected WBPH populations. Quantitative PCR analysis revealed that Asaia sp. were significantly more abundant in WBPH females than males, and mainly distributed in the guts, fatty bodies, and salivary glands. Asaia-infected WBPH were of shorter nymphal duration and heavier adult weight than Asaia-free WBPH, while Asaia-free WBPH comparatively fed more, indicating that Asaia plays a role in improving WBPH fitness through involvement in host’s nutrient supply.

Highlights

Insects are colonized by a complex microbial population in a symbiotic relationship (Dillon and Dillon, 2004; Moran et al, 2008)
The present study further confirmed the presence of Asaia in white-backed planthopper (WBPH) via diagnostic PCR using the 16S rRNA gene (Table 3) and transmission electron microscopy (TEM) observation (Figure 1)
The reason may be that the Asaia in A. gambiae is vertically transmitted at 100% (Damiani et al, 2010), while the Asaia in WBPH is vertically transmitted at 30% (Table 3)

Summary

Introduction

Insects are colonized by a complex microbial population in a symbiotic relationship (Dillon and Dillon, 2004; Moran et al, 2008) These associations have been formed between symbionts and host insects during long evolutionary processes that are generally categorized as: mutualism, commensalism, and parasitism (Werren et al, 2008; Frago et al, 2012). Asaia co-existing with plasmodium parasites in the guts and salivary glands of A. stephensi play an immunity regulatory role through activating the expression of host antimicrobial peptides without inhibiting itself, leading to the possibility of introducing Asaia as a strong contender for malaria vector control via paratransgenesis technology (Favia et al, 2007; Damiani et al, 2010; Capone et al, 2013; Rami et al, 2018). Asaia were detected in the small brown planthopper (SBPH, Laodelphax striatellus) and the brown planthopper (BPH, Nilaparvata lugens) through 16S rDNA high-throughput sequencing technology (Li et al, 2017; Zhang et al, 2019)

Methods

Results

Conclusion