An eco-systems biology approach for modeling tritrophic networks reveals the influence of dietary amino acids on symbiont dynamics of Bemisia tabaci

International audienceMetabolic conversions allow organisms to produce essential metabolites from the available nutrients in an environment, frequently requiring metabolic exchanges among co-inhabiting organisms. Here, we applied genomic-based simulations for exploring tri-trophic interactions among the sap-feeding insect whitefly (Bemisia tabaci), its host-plants, and symbiotic bacteria. The simplicity of this ecosystem allows capturing the interacting organisms (based on genomic data) and the environmental content (based on metabolomics data). Simulations explored the metabolic capacities of insect-symbiont combinations under environments representing natural phloem. Predictions were correlated with experimental data on the dynamics of symbionts under different diets. Simulation outcomes depict a puzzle of three-layer origins (plant-insect-symbionts) for the source of essential metabolites across habitats and stratify interactions enabling the whitefly to feed on diverse hosts. In parallel to simulations, natural and artificial feeding experiments provide supporting evidence for an environment-based effect on symbiont dynamics. Based on simulations, a decrease in the relative abundance of a symbiont can be associated with a loss of fitness advantage due to an environmental excess in amino-acids whose production in a deprived environment used to depend on the symbiont. The study demonstrates that genomic-based predictions can bridge environment and community dynamics and guide the design of symbiont manipulation strategies

Rickettsia ‘In’ and ‘Out’: Two Different Localization Patterns of a Bacterial Symbiont in the Same Insect Species

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<i>Bemisia tabaci</i> lines studied.

a<p>Data from Chiel et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0021096#pone.0021096-Chiel1" target="_blank">[18]</a>, Gottlieb et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0021096#pone.0021096-Gottlieb1" target="_blank">[20]</a>.</p

FISH of <i>Bemisia tabaci</i> nymphs parasitized by <i>Eretmocerus mundus</i>.

<p>The procedure was performed using <i>Portiera</i>-specific probe (red) and <i>Rickettsia-</i>specific probe (blue). (<b>A</b>) Scattered (S) localization pattern. White arrows indicate bacteriocytes. Blue-speckled area is the whitefly hemocoel, and the dark, clear area corresponds to the outline of the roughly spherical <i>Eretmocerus</i> larva. Bright blue area (black arrow) shows the wasp larval gut. (<b>B</b>) Confined (C) localization pattern. (<b>B1</b>) Red area (white arrows) shows <i>Portiera</i> in the bacteriocytes (<b>B2</b>) Blue area (white arrows) shows <i>Rickettsia</i> in the bacteriocytes. The pictures of <i>Rickettsia</i> and <i>Portiera</i> are presented separately because of the faint signal seen by the former. Other blue and red areas in the pictures are due to autofluorescence of the whitefly nymph and the shell of the wasp's hatched egg (white dashed arrow).</p

PCR primer sets used in this study.

a<p>Internal primers.</p

The Transmission Efficiency of Tomato Yellow Leaf Curl Virus by the Whitefly Bemisia tabaci Is Correlated with the Presence of a Specific Symbiotic Bacterium Species▿

Tomato yellow leaf curl virus (TYLCV) (Geminiviridae: Begomovirus) is exclusively vectored by the whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae). TYLCV transmission depends upon a 63-kDa GroEL protein produced by the vector's endosymbiotic bacteria. B. tabaci is a species complex comprising several genetically distinct biotypes that show different secondary-symbiont fauna. In Israel, the B biotype harbors Hamiltonella, and the Q biotype harbors Wolbachia and Arsenophonus. Both biotypes harbor Rickettsia and Portiera (the obligatory primary symbionts). The aim of this study was to determine which B. tabaci symbionts are involved in TYLCV transmission using B. tabaci populations collected in Israel. Virus transmission assays by B. tabaci showed that the B biotype efficiently transmits the virus, while the Q biotype scarcely transmits it. Yeast two-hybrid and protein pulldown assays showed that while the GroEL protein produced by Hamiltonella interacts with TYLCV coat protein, GroEL produced by Rickettsia and Portiera does not. To assess the role of Wolbachia and Arsenophonus GroEL proteins (GroELs), we used an immune capture PCR (IC-PCR) assay, employing in vivo- and in vitro-synthesized GroEL proteins from all symbionts and whitefly artificial feeding through membranes. Interaction between GroEL and TYLCV was found to occur in the B biotype, but not in the Q biotype. This assay further showed that release of virions protected by GroEL occurs adjacent to the primary salivary glands. Taken together, the GroEL protein produced by Hamiltonella (present in the B biotype, but absent in the Q biotype) facilitates TYLCV transmission. The other symbionts from both biotypes do not seem to be involved in transmission of this virus

Genomic characterization of viruses associated with the parasitoid Anagyrus vladimiri (Hymenoptera: Encyrtidae)

International audienceKnowledge on symbiotic microorganisms of insects has increased dramatically in recent years, yet relatively little data are available regarding non-pathogenic viruses. Here we studied the virome of the parasitoid wasp Anagyrus vladimiri Triapitsyn (Hymenoptera: Encyrtidae), a biocontrol agent of mealybugs. By high-throughput sequencing of viral nucleic acids, we revealed three novel viruses, belonging to the families Reoviridae [provisionally termed AnvRV (Anagyrus vladimiri reovirus)], Iflaviridae (AnvIFV) and Dicistroviridae (AnvDV). Phylogenetic analysis further classified AnvRV in the genus Idnoreovirus , and AnvDV in the genus Triatovirus . The genome of AnvRV comprises 10 distinct genomic segments ranging in length from 1.5 to 4.2 kb, but only two out of the 10 ORFs have a known function. AnvIFV and AnvDV each have one polypeptide ORF, which is typical of iflaviruses but very un-common among dicistroviruses. Five conserved domains were found along both the ORFs of those two viruses. AnvRV was found to be fixed in an A. vladimiri population that was obtained from a mass rearing facility, whereas its prevalence in field-collected A. vladimiri was ~15 %. Similarly, the prevalence of AnvIFV and AnvDV was much higher in the mass rearing population than in the field population. The presence of AnvDV was positively correlated with the presence of Wolbachia in the same individuals. Transmission electron micrographs of females’ ovaries revealed clusters and viroplasms of reovirus-like particles in follicle cells, suggesting that AnvRV is vertically transmitted from mother to offspring. AnvRV was not detected in the mealybugs, supporting the assumption that this virus is truly associated with the wasps. The possible effects of these viruses on A. vladimiri ’s biology, and on biocontrol agents in general, are discussed. Our findings identify RNA viruses as potentially involved in the multitrophic system of mealybugs, their parasitoids and other members of the holobiont