Nematode-Bacterium Symbioses—Cooperation and Conflict Revealed in the “Omics” Age

Nematodes are ubiquitous organisms that have a significant global impact on ecosystems, economies, agriculture, and human health. The applied importance of nematodes and the experimental tractability of many species have promoted their use as models in various research areas, including developmental biology, evolutionary biology, ecology, and animal-bacterium interactions. Nematodes are particularly well suited for the investigation of host associations with bacteria because all nematodes have interacted with bacteria during their evolutionary history and engage in a variety of association types. Interactions between nematodes and bacteria can be positive (mutualistic) or negative (pathogenic/parasitic) and may be transient or stably maintained (symbiotic). Furthermore, since many mechanistic aspects of nematode-bacterium interactions are conserved, their study can provide broader insights into other types of associations, including those relevant to human diseases. Recently, genome-scale studies have been applied to diverse nematode-bacterial interactions and have helped reveal mechanisms of communication and exchange between the associated partners. In addition to providing specific information about the system under investigation, these studies also have helped inform our understanding of genome evolution, mutualism, and innate immunity. In this review we discuss the importance and diversity of nematodes, “omics”' studies in nematode-bacterial systems, and the wider implications of the findings

Burkholderia as bacterial symbionts of Lagriinae beetles: symbiont transmission, prevalence and ecological significance in Lagria villosa and Lagria hirta (Coleoptera: Tenebrionidae)

Dissertation: Burkholderia as bacterial symbionts of Lagriinae beetles Laura Victoria Flórez Friedrich-Schiller-Universität Jena, Nov. 2016 Symbiosis is ubiquitous in nature and can play a crucial role in shaping the biology of both eukaryotes and prokaryotes. Importantly, the interaction of microorganisms with eukaryotes can range from pathogenicity to mutualism, also shifting along this continuum. The ecological settings facilitating such lifestyle transitions are, however, poorly understood. This dissertation focuses on the symbiosis between Lagriinae beetles and Burkholderia gladioli, a bacterium mostly known for its plant pathogenic traits. In Lagria hirta and Lagria villosa beetles, I localized these bacteria on adults, larvae and eggs of both species confirming a vertical transmission route. The presence of B. gladioli in these and four other Lagriinae species suggested that the association is relatively ancient and evolved within this phytopathogenic bacterial group. Additionally, B. gladioli from L. villosa can successfully infect soybean plants, a food source for this beetle species, and negatively affect the plant’s reproductive output, implying that the insect symbiont conserves the ability to intimately interact with a plant. Presumably, the potential of plant pathogenic B. gladioli bacteria to produce potent bioactive substances was also essential for establishing a mutualism with the insect. In L. villosa beetles, I could show that B. gladioli on the surface of eggs inhibit the growth of antagonistic fungi. I thereby demonstrate a symbiont-mediated defense, which could be highly advantageous at the nutrient-rich and immobile egg stage. Furthermore, we elucidated four compounds (toxoflavin, caryoynencin, lagriene and lagriamide) that could be responsible for the protective effect by the symbionts. Finally, multiple symbiotic B. gladioli strains were found coexisting in individual beetles, bringing about interesting questions regarding the potential advantages of strain diversity in defensive symbiosis and the evolutionary dynamics supporting their long-term maintenance

Bacterial ectosymbionts in cuticular organs chemically protect a beetle during molting stages

In invertebrates, the cuticle is the first and major protective barrier against predators and pathogen infections. While immune responses and behavioral defenses are also known to be important for insect protection, the potential of cuticle-associated microbial symbionts to aid in preventing pathogen entry during molting and throughout larval development remains unexplored. Here, we show that bacterial symbionts of the beetle Lagria villosa inhabit unusual dorsal invaginations of the insect cuticle, which remain open to the outer surface and persist throughout larval development. This specialized location enables the release of several symbiont cells and the associated protective compounds during molting. This facilitates ectosymbiont maintenance and extended defense during larval development against antagonistic fungi. One Burkholderia strain, which produces the antifungal compound lagriamide, dominates the community across all life stages, and removal of the community significantly impairs the survival probability of young larvae when exposed to different pathogenic fungi. We localize both the dominant bacterial strain and lagriamide on the surface of eggs, larvae, pupae, and on the inner surface of the molted cuticle (exuvia), supporting extended protection. These results highlight adaptations for effective defense of immature insects by cuticle-associated ectosymbionts, a potentially key advantage for a ground-dwelling insect when confronting pathogenic microbes. [Image: see text

Molekulare Charakterisierung und Lokalisationsmuster zweier putativer Bakterien-permeabilisierender Proteine (BPI) eines marinen symbiotischen Nematoden

Der stilbonematide Nematode Laxus oneistus ist bedeckt mit Sulfid-oxidierenden Gammaproteobakterien. Diese gehören einem einzigen 16S rRNA-Gen Phylotyp an. Die Besiedlung der Kutikula des Nematoden durch diese Bakterien beschränkt sich auf die posteriore Region, während die anteriore Region nicht kolonisiert wird. Wir haben zwei L. oneistus Gene charakterisiert, welche für Mitglieder der Genfamilie Bakterien-permeabilisierender (BPI)/Lipopolysaccharid-bindender Proteine (LBP) kodieren. Basierend auf transkriptomalen Daten haben wir Primer designed um die vollständigen cDNA Sequenzen zu amplifizieren und zu klonieren, welche bestätigten dass sie für sekretierte Proteine kodieren. Lo-BPI1 und Lo-BPI2 zeigen 42.5-51.1% Sequenzähnlichkeit mit anderen Invertebraten-BPI Proteinen und 40.5% Ähnlichkeit mit humanem BPI. Außerdem weisen alle Proteine ähnliche strukturelle Eigenschaften auf. Phylogenetisch gruppieren sich die Lo-BPI Proteine mit Protostomia-Orthologen, nämlich mit anderen LBP/BPI Proteinen mariner Invertebraten und einer hypothetischen Proteinsequenz eines parasitischen Nematoden. Basierend auf Western Blot Analysen werden Lo-BPI1 and 2 von adulten L. oneistus Individuen exprimiert. Die Analyse des Lokalisationsmusters hat ergeben, dass die hypodermalen Drüsen BPI1 und 2 in beiden Regionen des Nematoden absondern und dass die Proteine und der Ektosymbiont kolokalisieren. Dies lässt vermuten, dass durch die erwartete antimikrobielle Wirkung von BPI1 and 2 eine Besiedlung der Kutikula durch nicht-symbiotische und potentiell schädliche Gram-negative Bakterien verhindert wird, während der Ektosymbiont unbeeinträcht bleibt. Die Spezifität der Symbiose könnte durch das Zusammenspiel eines zuvor identifizierten Symbionten-bindenden Lektins und den Lo-BPI Proteinen gewährleistet werden.The stilbonematid nematode Laxus oneistus is coated with sulphur-oxidizing Gammaproteobacteria. These belong to a single 16S rRNA-gene phylotype and are restricted to the posterior region of the nematode cuticle. The anterior part, instead, is left uncolonized. We characterized two L. oneistus genes encoding for members of the bactericidal/permeability increasing (BPI)/lipopolysaccharide-binding (LBP) protein superfamily. Based on transcriptomic data, we designed primers to amplify and clone the full-length cDNA sequences, which confirmed that they both encode for secreted proteins. Lo-BPI1 and Lo-BPI2 show 42.5-51.1% sequence similarity to other invertebrate BPIs and 40.5% similarity to human BPI, as well as structural similarities. The Lo-BPI proteins phylogenetically cluster with protostomian orthologs, represented by other LBP/BPI proteins from marine invertebrates and one hypothetical protein sequence from a parasitic nematode. Based on western blot analysis, Lo-BPI1 and 2 are expressed by adult L. oneistus individuals. Localization pattern analysis via immunostaining revealed that the hypodermal glands secrete BPI1 and 2 throughout the nematode, and that the proteins colocalize with the ectosymbiont. This suggests that, instead of affecting the ectosymbiont, the predicted antimicrobial action of BPI1 and 2 may prevent cuticle colonization by non-symbiotic and potentially deleterious Gram-negative bacteria. Together with a previously identified symbiont-binding lectin, the Lo-BPI proteins could mediate the specificity of the symbiosis

Characterization of bacterial endo- and ectosymbionts of oligochaete worms from marine sediments: Phylogeny and metabolic potential

Two obligate bacterial endosymbioses and a facultative ectosymbiosis of gutless (1, 2) and gut-bearing (3) marine oligochaetes from coastal sediments were characterized. (1, 2) The gutless oligochaetes Olavius algarvensis and O. ilvae live in coastal sediments with very low sulfide concentrations. Similar bacterial consortia were found in both hosts with two sulfide-oxidizing Gammaproteobacteria and two sulfate-reducing Deltaproteobacteria. The presence of sulfate-reducers providing the sulfide-oxidiziers with an internal source of sulfide could explain how the worms could colonize a sulfide-poor environment. (3) Tubificoides benedii lives in Wadden Sea sediments and is adapted to extreme fluctuations of oxygen and sulfide. Its posterior end is facultatively colonized by filamentous bacteria. This community was dominated by two morphologically distinct phylotypes: A thicker Gammaproteobacterium attached to the exterior of the cuticle and a thinner Epsilonproteobacterium penetrated it. Both ectosymbionts belonged to clades that consisted nearly exclusively of bacteria associated with deep-sea hydrothermal vent invertebrates

Aphrophoridae role in Xylella fastidiosa subsp. Pauca ST53 invasion in southern Italy

The Philaenus spumarius L. (Hemiptera Aphrophoridae) is a xylem-sap feeder vector that acquires Xylella fastidiosa subsp. pauca ST53 during feeding on infected plants. The bacterium is the plant pathogen responsible for olive quick decline syndrome that has decimated olive trees in Southern Italy. Damage originates mainly from the insect vector attitude that multiplies the pathogen potentialities propagating Xf in time and space. The principal action to manage insect-borne pathogens and to contain the disease spread consists in vector and transmission control. The analysis of an innovative and sustainable integrated pest management quantitative strategy that targets the vector and the infection by combining chemical and physical control means demonstrates that it is possible to stop the Xylella invasion. This review updates the available topics addressing vectors’ identification, bionomics, infection management, and induced disease by Xylella invasion to discuss major available tools to mitigate the damage consequent to the disease