Culex pipiens and Culex restuans egg rafts harbor diverse bacterial communities compared to their midgut tissues

Elijah O Juma,Christopher Dunlap,Chris M Stone,Chang-Hyun Kim,Brian F Allan

doi:10.1186/s13071-020-04408-4

Abstract

BackgroundThe bacterial communities associated with mosquito eggs are an essential component of the mosquito microbiota, yet there are few studies characterizing and comparing the microbiota of mosquito eggs to other host tissues.MethodsWe sampled gravid female Culex pipiens L. and Culex restuans Theobald from the field, allowed them to oviposit in the laboratory, and characterized the bacterial communities associated with their egg rafts and midguts for comparison through MiSeq sequencing of the 16S rRNA gene.ResultsBacterial richness was higher in egg rafts than in midguts for both species, and higher in Cx pipiens than Cx. restuans. The midgut samples of Cx. pipiens and Cx. restuans were dominated by Providencia. Culex pipiens and Cx. restuans egg rafts samples were dominated by Ralstonia and Novosphingobium, respectively. NMDS ordination based on Bray-Curtis distance matrix revealed that egg-raft samples, or midgut tissues harbored similar bacterial communities regardless of the mosquito species. Within each mosquito species, there was a distinct clustering of bacterial communities between egg raft and midgut tissues.ConclusionThese findings expand the list of described bacterial communities associated with Cx. pipiens and Cx. restuans and the additional characterization of the egg raft bacterial communities facilitates comparative analysis of mosquito host tissues, providing a basis for future studies seeking to understand any functional role of the bacterial communities in mosquito biology.

Highlights

Studies applying high throughput, culture-independent sequencing of the bacterial 16S rRNA gene have advanced understanding of the association between mosquitoes and their bacterial communities [1,2,3,4]
Studies with Aedes aegypti and Ae. triseriatus have shown that bacterial density on the egg surface mediates egg hatch rates and timeto-hatch, while mosquito eggs subjected to heavy larval grazing in high larval density habitats can exhibit delayed time-to-hatch [16,17,18]
Culex pipiens egg-raft samples had significantly higher observed and expected (Chao1) bacterial operational taxonomic unit (OTU) richness compared to Cx. pipiens midgut samples, or Cx. restuans egg-raft and midgut samples

Summary

Introduction

Culture-independent sequencing of the bacterial 16S rRNA gene have advanced understanding of the association between mosquitoes and their bacterial communities [1,2,3,4]. The bulk of studies characterizing mosquito-associated bacterial communities have focused on the mosquito gut. Other mosquito organs or tissues, including the ovaries, the male reproductive system, the salivary glands, and eggs, are known to harbor bacterial communities that may play essential roles in mosquito biology [5,6,7,8,9,10,11]. Mosquito egg bacterial communities likely play important roles in mosquito ecology. To what extent the bacterial communities on the egg surface drive the hatching effect relative to the microbes in the water column remains unclear. The bacterial communities associated with mosquito eggs are an essential component of the mos‐ quito microbiota, yet there are few studies characterizing and comparing the microbiota of mosquito eggs to other host tissues

Methods

Results

Conclusion