Activated entomopathogenic nematode infective juveniles release lethal venom proteins

Abstract

Entomopathogenic nematodes (EPNs) are unique parasites due to their symbiosis with entomopathogenic bacteria and their ability to kill insect hosts quickly after infection. It is widely believed that EPNs rely on their bacterial partners for killing hosts. Here we disproved this theory by demonstrating that the in vitro activated infective juveniles (IJs) of Steinernema carpocapsae (a well-studied EPN species) release venom proteins that are lethal to several insects including Drosophila melanogaster. We confirmed that the in vitro activation is a good approximation of the in vivo process by comparing the transcriptomes of individual in vitro and in vivo activated IJs. We further analyzed the transcriptomes of non-activated and activated IJs and revealed a dramatic shift in gene expression during IJ activation. We also analyzed the venom proteome using mass spectrometry. Among the 472 venom proteins, proteases and protease inhibitors are especially abundant, and toxin-related proteins such as Shk domain-containing proteins and fatty acid- and retinol-binding proteins are also detected, which are potential candidates for suppressing the host immune system. Many of the venom proteins have conserved orthologs in vertebrate-parasitic nematodes and are differentially expressed during IJ activation, suggesting conserved functions in nematode parasitism. In summary, our findings strongly support a new model that S. carpocapsae and likely other Steinernema EPNs have a more active role in contributing to the pathogenicity of the nematode-bacterium complex than simply relying on their symbiotic bacteria. Furthermore, we propose that EPNs are a good model system for investigating vertebrate- and human-parasitic nematodes, especially regarding the function of excretory/secretory products.

Control of the banded fruit weevil Phlyctinus callosus (Coleoptera: Curculionidae) using entomopathogenic nematodes

“…The nematodes, on their own, are able to kill the host insect but, together with their symbiotic bacteria, are highly virulent (Lu et al . ).…”

Partner-specific induction ofSpodoptera frugiperdaimmune genes in response to the entomopathogenic nematobacterial complexSteinernema carpocapsae-Xenorhabdus nematophila

“…The only characterized IMPI encodes two proteins of which one is probably involved in the regulation of extracellular matrix remodeling and the second specifically targets metalloproteinases from pathogens (113, 114). S. carpocasape and X. nematophila both express several secreted serine proteases as well as metalloproteinases during the infectious process (39, 115–120). The induction of such immune responses could interfere with some of these proteinases to impair the NBC’s virulence and/or survival.…”

Adapting the Smart-seq2 Protocol for Robust Single Worm RNA-seq

“…Paired-end S. carpocapsae RNA-seq data from Lu et al (2017) can be downloaded at GEO under accession GSE89961 .…”

“…, 2013 and 2014; Trombetta et al , 2014), for single nematode RNA-sequencing. We successfully utilized adapted versions of this protocol in the transcriptomic analysis of the insect-parasitic nematode, Steinernema carpocapsae (Lu et al ., 2017) as well as in the analysis of individual embryos and L1 larvae from two Steinernema and two Caenorhabditis species including C. elegans (Macchietto et al ., 2017), but this protocol can be adapted for any species of nematode. While this protocol will work on nematodes without already sequenced genomes or transcriptomes, we limit our computational analysis to organisms with published genome annotations, such as S. carpocapsae (Dillman et al ., 2015).…”