A ribosome-inactivating protein in a Drosophila defensive symbiont

Abstract

Vertically transmitted symbionts that protect their hosts against parasites and pathogens are well known from insects, yet the underlying mechanisms of symbiont-mediated defense are largely unclear. A striking example of an ecologically important defensive symbiosis involves the woodland fly Drosophila neotestacea, which is protected by the bacterial endosymbiont Spiroplasma when parasitized by the nematode Howardula aoronymphium. The benefit of this defense strategy has led to the rapid spread of Spiroplasma throughout the range of D. neotestacea, although the molecular basis for this protection has been unresolved. Here, we show that Spiroplasma encodes a ribosome-inactivating protein (RIP) related to Shiga-like toxins from enterohemorrhagic Escherichia coli and that Howardula ribosomal RNA (rRNA) is depurinated during Spiroplasma-mediated protection of D. neotestacea. First, we show that recombinant Spiroplasma RIP catalyzes depurination of 28S rRNAs in a cell-free assay, as well as Howardula rRNA in vitro at the canonical RIP target site within the α-sarcin/ricin loop (SRL) of 28S rRNA. We then show that Howardula parasites in Spiroplasma-infected flies show a strong signal of rRNA depurination consistent with RIP-dependent modification and large decreases in the proportion of 28S rRNA intact at the α-sarcin/ricin loop. Notably, host 28S rRNA is largely unaffected, suggesting targeted specificity. Collectively, our study identifies a novel RIP in an insect defensive symbiont and suggests an underlying RIP-dependent mechanism in Spiroplasma-mediated defense.symbiosis | male-killing | Spiroplasma | Shiga toxin | nematode

Generality of toxins in defensive symbiosis: Ribosome-inactivating proteins and defense against parasitic wasps in Drosophila

“…neotestacea , and that depurinates at the α-sarcin/ricin loop of eukaryotic 28S rRNA [32,40]. Interestingly, the Spiroplasma from D .…”

“…Furthermore, infection experiments revealed that nematodes that infect flies harbouring Spiroplasma exhibit the hallmarks of attack by RIP toxins, including massive increases in levels of depurinated ribosomes [40]. Intriguingly, the genome of the Spiroplasma symbiont of D .…”

Functional variation in the gut microbiome of wild Drosophila populations

“…The great majority of animals harbour gut microorganisms of variable composition (Brooks, Kohl, Brucker, van Opstal & Bordenstein, ; McFall‐Ngai et al., ), and there is increasing evidence that this microbial variation can influence the phenotype of the host (Hamilton, Peng, Boulanger & Perlman, ; Kohl, Weiss, Cox, Dale & Dearing, ; Sampson et al., ; Surana & Kasper, ). However, most of the studies investigating the relationship between the gut microbiome and host traits have two important limitations.…”

Cultivable Bacterial Diversity in the Gut of the Chagas Disease Vector Triatoma dimidiata: Identification of Possible Bacterial Candidates for a Paratransgenesis Approach

“…For example, protection against a virulent nematode (Howardula aoronymphium) by Spiroplasma through the production of a toxin has been observed in Drosophila neotestacea, illustrating the positive effect these interactions can have in the defense system of the hosts (Douglas, 2011;Hamilton et al, 2015). Another example is the bacteria in the digestive tract of insects that appear to be necessary for detoxification of plant material (Bugg et al, 2011).…”