High-Resolution Infection Kinetics of Entomopathogenic Nematodes Entering Drosophila melanogaster

Alexis Dziedziech,Ulrich Theopold,Sai Shivankar

doi:10.3390/insects11010060

Abstract

Entomopathogenic nematodes (EPNs) have been a useful model for studying wound healing in insects due to their natural mechanism of entering an insect host either through the cuticle or an orifice. While many experiments have shed light on nematode and host behavior, as well as the host immune response, details regarding early nematode entry and proliferative events have been limited. Using high-resolution microscopy, we provide data on the early infection kinetics of Heterorhabditis bacteriophora and its symbiotic bacteria, Photorhabdus luminescens. EPNs appendage themselves to the host and enter through the host cuticle with a drill-like mechanism while leaving their outer sheath behind. EPNs immediately release their symbiotic bacteria in the host which leads to changes in host behavior and septicemia within 6 h while EPNs travel through the host in a predictable manner, congregating in the anterior end of the host. This paper sheds light on the entry and proliferative events of EPN infection, which will further aid in our understanding of wound healing and host immune activation at a high spatiotemporal resolution.

Highlights

Nematodes are a diverse clade of organisms that infect many species, including vertebrates and invertebrates
In order to follow the Entomopathogenic nematodes (EPNs) H. bacteriophora in its effort to gain entry into the hemocoel of Drosophila larvae, we used a combination of H. bacteriophora and its symbiotic counterpart, Photorhabdus luminescens, which contained a GFP-expressing plasmid [1]
We exposed w1118 larvae to high titers of EPNs, 500 Infective juveniles (IJs)/10 μL/larva, for 30 to 45 min until larvae were swarmed with many EPNs; EPNs preferred some individual larvae compared to other nearby larvae

Summary

Introduction

Nematodes are a diverse clade of organisms that infect many species, including vertebrates and invertebrates. EPNs parasitize Lepidopteran species as well as Drosophila larvae, which in turn serve as a model for understanding the host immune response against nematode infections in general, like in the case of Elephantiasis or Onchocerciasis. They enter the host through either the mouth or anus or use their hook-like tooth to burrow into the cuticle, past the epithelial layer to reach the hemocoel. Steinernema have been reported to be more pathogenic to the Drosophila host [4] Perhaps one reason these EPNs have different infection strategies and pathogenicity is that they are not closely related and underwent divergent evolution, including their parasitization strategy [5,6]

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