243 research outputs found
Dynamics and molecular mechanisms aiding symbiont establishment in Lagria villosa beetles
No full textMany animals live in a symbiotic relationship with microbial partners. Among them, beneficial host-associated microorganisms may provide nutritional benefits, protect the host from antagonists, or help in detoxifying harmful compounds. To maintain a stable association, animal hosts vertically transmit symbionts to the offspring, acquire them horizontally from an external source, or carry out both transmission modes. In horizontal and mixed transmission modes, host molecular factors are necessary to screen for the right microbial partners from the environment, and microbial machineries help the symbionts gain entry and establish in the host. However, we know little about molecular factors that mediate symbiont establishment in invertebrates harbouring ectosymbionts. To expand our knowledge, I studied the defensive symbiotic association between Lagria villosa beetles and Burkholderia bacteria. Here, the female Lagria beetles smear symbionts on the egg surface during oviposition. The symbionts colonize three specialized cuticular invaginations on the dorsal surface of the larvae. On eggs and in the larvae, the symbionts produce antifungal compounds and protect the beetle from antagonists. Furthermore, the larvae can occasionally acquire symbionts from the external environment; therefore, they maintain a mixed transmission mode. Among the multiple strains of Burkholderia usually found in an individual, Burkholderia Lv-StB is the most dominant strain, but is uncultivable in the lab. However, Burkholderia gladioli Lv-StA that is occasionally found in the beetles, is cultivable. The ability to rear the beetles in the lab and cultivate one of the symbionts in vitro gives us the opportunity to study host and symbiont molecular factors involved in symbiont establishment. In this dissertation, first, I provide details on the dynamics and mechanisms of symbiont colonization. Symbionts colonize the dorsal structures of the larvae during hatching and a colonization time-window may restrict microbial entry into the host. Further, a transposon-insertion directed sequencing (Tn-seq) method was established in the lab using which 271 potential colonization factors in Lv-StA were identified, including motility, biofilm formation, cell wall structures, lipopeptides, oxidative stress response factors and iron scavenging molecules. Additionally, targeted mutagenesis and colonization assays with Lv-StA reveal that non-motile strains can still colonize the host, and this likely explains the loss of flagellar motility genes in Lv-StB, which has a more reduced genome than Lv-StA. Finally, by performing gene expression analysis across multiple developmental time points in symbiotic and aposymbiotic beetles, the host molecular responses in the presence of Lv-StB was investigated. It reveals that the host may not recognise symbiont presence, likely due to compartmentalization, or may have a constitutive response to the symbionts. Thus, combining our understanding of both host and symbiont molecular factors involved in establishment, interesting questions regarding how partner specificity is achieved in ectosymbioses, are revealed. This study gives us the opportunity to understand the mechanistic details of host – symbiont interactions and further to compare emerging patterns across other model and non-model systems.xii, 181 Seiten ; Illustrationen, Diagramm
Blanking on blanks: few insect microbiota studies control for contaminants.
Get PDFResearch on insect-microbe relationships is booming, with DNA sequencing being the most commonly used method to describe insect microbiota. However, sequencing is vulnerable to contamination, especially when the sample has low microbial biomass. Such low-biomass samples are common across insect taxa, developmental stages, and tissue types. Identifying putative contaminants is essential to distinguish between true microbiota and introduced contaminant DNA. It is therefore important that studies control for contamination, but how often this is done is unknown. To investigate the status quo of contamination control, we undertook a systematic literature review to quantify the prevalence of negative control usage and contamination control across the literature on insect microbiota (specifically bacterial communities) over a 10 year period. Two-thirds of the 243 insect microbiota studies evaluated had not included blanks (negative controls), and only 13.6% of the studies sequenced these blanks and controlled for contamination in their samples. Our findings highlight a major lack of contamination control in the field of insect microbiota research. This result suggests that a number of microbes reported in the literature may be contaminants as opposed to insect-associated microbiota and that more rigorous contamination control is needed to improve research reliability, validity, and reproducibility. Based on our findings, we recommend the previously developed guidelines outlined in the RIDE checklist, with the addition of one more guideline. We refer to this as the RIDES checklist, which stands for Report methodology, Include negative controls, Determine the level of contamination, Explore contamination downstream, and State the amount of off-target amplification.IMPORTANCEOur systematic review reveals a major lack of methodological rigor within the field of research on insect-associated microbiota. The small percentage of studies that control for contamination suggests that an unknown but potentially considerable number of bacteria reported in the literature could be contaminants. The implication of this finding is that true microbiota may be masked or misrepresented, especially in insects with low microbial biomass
Host adaptation protects a defensive symbiont during vertical transmission in beewolf wasps (Hymenoptera: Crabronidae)
Get PDFMicrobial symbioses are ubiquitous in insects, and present key drivers of evolutionary innovation. To
stabilize a symbiosis over long evolutionary timescales, the symbiont must be reliably transmitted to
the next host generation. Vertically transmitted extracellular symbionts commonly face prolonged
periods outside of the stable host environment during transmission, entailing exposure to diverse
biotic and abiotic threats. These threats should be exacerbated in insect symbionts of evolutionary
ancient associations, which generally possess eroded genomes with reduced genetic inventories.
While external transmission is widespread among the Hemiptera, Hymenoptera, Coleoptera and
Diptera, the mechanism protecting the symbionts from environmental threats during transmission
remain poorly studied.
In this dissertation, I employ the defensive symbiosis of the European beewolf Philanthus triangulum
(Hymneoptera: Crabronidae) and the Actinobacterium ‘Candidatus Streptomyces philanthi’
(henceforth S. philanthi) to investigate how a symbiont with an eroded genome copes with a host-derived exogenous challenge during vertical transmission in an evolutionary ancient symbiosis. Female
beewolves provide their brood cells with a symbiont-containing secretion, from which S. philanthi is
later transferred to the cocoon to protect the offspring from microbial opportunists by producing
antibiotics. In the brood cell, this secretion is exposed to extremely high concentrations of toxic nitric
oxide (NO) emitted by the beewolf egg, which effectively kills antagonistic microbes. How S. philanthi
withstands the lethal burst of NO remained unknown.
I show that the symbiont’s global stress response to NO is not sufficient to survive NO concentrations
mimicking brood cell-level concentrations in vitro. Instead, I demonstrate that the symbiont-
containing secretion consisting of long-chain hydrocarbons (HCs) forms an effective NO diffusion
barrier around S. philanthi, and additionally contains host-derived protective enzymes. While different
functions of an insect’s HC profile can exert conflicting selection pressures on its composition, in vitro
assays with beewolf-derived and synthetic HCs reveal that the NO diffusion barrier function of HCs in
P. triangulum does not constrain the insect’s multifunctional HC profile. My comparisons of HC profiles
across different beewolf hosts suggest their suitability for NO protection, and in vitro assays with their
respective symbionts indicate a widespread NO sensitivity. Given the shared ecology among
beewolves, as well as additional reports on NO defense in P. gibbosus and P. basilaris, NO fumigation
and the concomitant HC-mediated protection of the symbiont from NO is likely crucial across
beewolves.
My findings add a novel dimension to the plethora of functions of insect HCs, and constitute one of
the few examples of a host adaptation protecting a symbiont from a lethal threat during external
vertical transmission. I therefore illustrate a mechanism by which a symbiotic association can be
stabilized over long evolutionary timescales, an aspect essential to our general understanding of
microbial symbiosis.Mikrobielle Symbiosen sind allgegenwärtig in Insekten und stellen eine treibende Kraft für
evolutionäre Innovationen dar. Um eine Symbiose über lange evolutionäre Zeiträume zu stabilisieren
ist es erforderlich, dass der Symbiont zuverlässig auf die nächste Wirtsgeneration übertragen wird.
Vertikal übertragene extrazelluläre Symbionten verbringen während der Transmission oftmals längere
Zeiträume außerhalb des stabilen Wirtsmilieus, wobei sie mit diversen biotischen und abiotischen
Bedrohungen konfrontiert sind. Insektensymbionten in evolutionär alten Assoziationen sind aufgrund
ihrer erodierten Genome besonders anfällig gegenüber diesen Bedrohungen. Die externe
Symbiontentransmission ist zwar innerhalb der Ordnungen Hemiptera, Hymenoptera, Coleoptera und
Diptera weit verbreitet, dennoch sind die Mechanismen, die die Symbionten während dieser
Transmission vor Bedrohungen schützen, weitgehend unerforscht.
In dieser Dissertation untersuche ich anhand der evolutionär alten Verteidigungssymbiose des
Europäischen Bienenwolfes Philanthus triangulum (Hymenoptera: Crabronidae) mit dem
Actinobakterium ‘Candidatus Streptomyces philanthi’ (nachfolgend S. philanthi), wie ein Symbiont mit
einem erodierten Genom mit einer vom Wirt ausgehenden externen Bedrohung während der
vertikalen Transmission umgeht. Weibchen versehen ihre Brutzellen mit einem Sekret, das die
Symbionten beinhaltet. Die Symbionten werden zu einem späteren Zeitpunkt in den Kokon integriert,
wo sie Antibiotika zum Schutz der Brut vor opportunistischen Mikroben produzieren. Das Sekret ist in
der Brutzelle sehr hohen Konzentrationen toxischen Stickstoffmonoxids (NO) ausgesetzt, welches vom
Bienenwolf-Ei freigesetzt wird und antagonistische Mikroorganismen effektiv abtötet. Bisher war
unbekannt, wie die Symbionten den lethalen NO-Konzentrationen in der Brutzelle standhalten.
Ich zeige, dass die eigene Stressreaktion des Symbionten auf NO nicht ausreicht, um die in vitro
simulierten NO-Konzentrationen der Brutzelle zu überleben. Jedoch bildet das aus langkettigen
Kohlenwasserstoffen (KWs) bestehende Sekret, das die Symbionten umgibt, eine effektive NO-
Diffusionsbarriere um S. philanthi. Weiterhin enthält das Sekret vom Wirt produzierte Schutzenzyme.
Verschiedene Funktionen eines KW-Profils können gegensätzliche Selektionsdrücke auf seine
Komposition ausüben; allerdings zeigten in vitro-Experimente mit Bienenwolf- und synthetischen
KWs, dass die Fähigkeit, eine NO-Diffusionbarriere zu bilden, die Komposition des multifunktionalen
KW-Profils des Bienenwolfes nicht einschränkt. Vergleiche von KW-Profilen verschiedener
Bienenwolf-Wirte legen deren Eignung für eine NO-Barrierefunktion nahe, und in vitro-Experimente
mit den zugehörigen Symbionten weisen auf eine weit verbreitete NO-Sensitivität hin. Angesichts der
vergleichbaren Ökologie aller Bienenwölfe, sowie zusätzlicher Berichte über die Freisetzung von NO
in P. gibbosus und P. basilaris, ist der Einsatz von NO zu Verteidigungszwecken und der damit
einhergehende KW-vermittelte Symbiontenschutz wahrscheinlich von großer Bedeutung für alle
Bienenwölfe.
Meine Ergebnisse erweitern die Fülle an Funktionen von KWs in Insekten um eine neue Dimension,
und beschreiben eine der wenigen bekannten Wirtsadaptationen zum Schutz eines Symbionten vor
einer lethalen Bedrohung während der externen vertikalen Transmission. Sie illustrieren damit einen
Mechanismus, mithilfe dessen eine symbiotische Beziehung über lange evolutionäre Zeiträume
stabilisiert werden kann. Dieser Aspekt ist wesentlich für unser Verständnis von mikrobiellen
Symbiosen.VI, 126 Seiten; Illustrationen, Diagramme, Tabelle
Laudatio für Herrn Dr. Martin Kaltenpoth : anlässlich der Verleihung des Förderpreises der Ingrid Weiss / Horst Wiehe Stiftung durch der Deutschen Gesellschaft für allgemeine und angewandte Entomologie am 27. Februar 2007 in Innsbruck
No full textJeder der Anwesenden kennt die Faszination, die von den Leistungen und der Vielgestaltigkeit von Insekten ausgeht. Insekten bieten eine Fülle von Beispielen für die Evolution völlig neuartiger Strukturen, Verhaltensweisen, Verteidigungsmechanismen usw. Man denke z.B. an die Evolution der Flügel, die Tanzsprache der Bienen, die Evolution hochkomplexen Sozialverhaltens oder das chemische Fachwissen der Bombardierkäfer. Besonders faszinierend wird es dort, wo Insekten mit anderen Organismen interagieren. Berühmt geworden sind die z. B. die symbiotischen Beziehungen zwischen verschiedenen Taxa von Ameisen und Pflanzen oder zwischen höheren Termiten und ihren Pilzgärten. Während Mikroorganismen meist als Krankheitserreger oder Konkurrenten für Insekten auftreten, gibt es auch einige Fälle in denen sich aus diesen negativen Beziehungen positive, ja sogar obligate mutualistische Beziehungen entwickelt haben. Dazu gehören die Darmsymbionten die von vielen Herbivoren „adoptiert“ wurden, um ihre nährstoffarme pflanzliche Nahrung besser ausnutzen zu können. Wir haben es einem der diesjährigen Preisträger, Herrn Dr. Martin Kaltenpoth, zu verdanken, dass wir seit kurzem ein weiteres aufregendes und völlig überraschendes Beispiel für eine Symbiose zwischen einem Insekt und einem Bakterium kennen
Actinobacteria as mutualists: general healthcare for insects?
No full textMutualistic microorganisms are well known to play a key role in providing nutrients for successful growth and reproduction in many insects. Several recent studies indicate that they can be equally important for the protection of the host and its nutritional resources against pathogen attack. In particular, different actinobacteria have been found to defend ants, beetles and wasps against detrimental microorganisms by producing antibiotics. The extraordinary abilities of actinobacteria to exploit a wide variety of carbon and nitrogen sources and their extensive repertoire of secondary metabolites probably predispose this group to engage in protective symbioses. Defensive mutualisms with actinobacteria might constitute a general and widespread theme in the ecology and evolution of arthropods, and the study of the secondary metabolites involved promises to uncover novel drug candidates for human medicine
Actinobacteria and the vitamin metabolism of firebugs: Characterizing a mutualism's specificity and functional importance
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