Comparative Phenotypic and Genomics Approaches Provide Insight into the Tripartite Symbiosis of Xenorhabdus bovienii with Steinernema Nematode and Lepidopteran Insect Hosts

Persistent Link:
http://hdl.handle.net/10150/596124
Title:
Comparative Phenotypic and Genomics Approaches Provide Insight into the Tripartite Symbiosis of Xenorhabdus bovienii with Steinernema Nematode and Lepidopteran Insect Hosts
Author:
McMullen, John George II
Issue Date:
2015
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Embargo:
Release 12-Jan-2017
Abstract:
Nematodes are highly diverse animals capable of interacting with almost every other form of life on Earth from general trophic interactions to intimate and persistent symbiotic associations. Much of their recognition originates from their various parasitic lifestyles. From an agricultural standpoint, plant parasitic nematodes are widely known for the destruction they can cause to crop plants, such as the case of the root-knot nematode Meloidogyne incognita, or livestock animals, like the Trichinella spiralis, which infects pigs and other animals. From a human health perspective, nematodes can cause many debilitating diseases, for example Wuchereria bancrofti, which is a causative agent of lymphatic filariasis or elephantiasis. However, not all parasitic nematodes have bad implications for human health. For instance, the diverse interactions of insect parasitic nematodes can be used to our benefit. Many of these species have been considered as biological control alternatives to different insect pests that wreak havoc on human, animal, and plant health. There still remain many questions surrounding their evolution, ecology, and physiological capabilities. Many of these taxa are hard to cultivate in the lab due to their complex and intimate lifestyles. Entomopathogenic nematodes (EPNs) are of great interest in agriculture because they vector insect pathogenic bacteria, which are capable of causing death to an insect host within 48 hours post-infection. Much of the molecular underpinnings in this system still remain to be discovered, from understanding the basic ability of these two organisms to associate with one another to genetically engineering more robust and host specific pathogens for application in the field. The focus of the research presented herein is on Steinernematidae nematodes and their bacterial symbionts. Specifically, it focused on the relationship between Xenorhabdus bovienii and its Steinernema hosts. Bioassays were designed to investigate insect virulence of X. bovienii alone in two Lepidoptera insect species with known differential susceptibility to Steinernema-Xenorhabdus pairs. A comparative genomic analysis was performed to compare different Xenorhabdus bovienii strains with observed variation in insect virulence. Results from this analysis demonstrated that virulent strains possess a type VI secretion system (T6SS) locus that is completely absent in strains with attenuated virulence. Bacterial competition assays between T6SS+ and T6SS- strains suggest this locus is involved in bacterial competition. Additionally, symbiont preference assays were carried out to investigate whether Steinernema hosts are able to discern between virulent and attenuated X. bovienii strains. Results from these assays revealed that Steinernema nematodes are able to distinguish between cognate and non-cognate X. bovienii symbionts, giving preference to virulent strains over those with attenuated virulence. Altogether these results provide further evidence that supports the notion that symbiont-switching events have occurred over the Steinernema-Xenorhabdus co-evolutionary history. Specifically, the competitive virulence of certain X. bovienii strains may have conferred them the ability to be selected by different Steinernema hosts, therefore contributing to the success of the nematode-bacterium partnership in being pathogenic to diverse insect hosts.
Type:
text; Electronic Thesis
Keywords:
insect virulence; Steinernema; type VI secretion system; Microbiology; host-symbiont switching
Degree Name:
M.S.
Degree Level:
masters
Degree Program:
Graduate College; Microbiology
Degree Grantor:
University of Arizona
Advisor:
Stock, S. Patricia

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titleComparative Phenotypic and Genomics Approaches Provide Insight into the Tripartite Symbiosis of Xenorhabdus bovienii with Steinernema Nematode and Lepidopteran Insect Hostsen_US
dc.creatorMcMullen, John George IIen
dc.contributor.authorMcMullen, John George IIen
dc.date.issued2015en
dc.publisherThe University of Arizona.en
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en
dc.description.releaseRelease 12-Jan-2017en
dc.description.abstractNematodes are highly diverse animals capable of interacting with almost every other form of life on Earth from general trophic interactions to intimate and persistent symbiotic associations. Much of their recognition originates from their various parasitic lifestyles. From an agricultural standpoint, plant parasitic nematodes are widely known for the destruction they can cause to crop plants, such as the case of the root-knot nematode Meloidogyne incognita, or livestock animals, like the Trichinella spiralis, which infects pigs and other animals. From a human health perspective, nematodes can cause many debilitating diseases, for example Wuchereria bancrofti, which is a causative agent of lymphatic filariasis or elephantiasis. However, not all parasitic nematodes have bad implications for human health. For instance, the diverse interactions of insect parasitic nematodes can be used to our benefit. Many of these species have been considered as biological control alternatives to different insect pests that wreak havoc on human, animal, and plant health. There still remain many questions surrounding their evolution, ecology, and physiological capabilities. Many of these taxa are hard to cultivate in the lab due to their complex and intimate lifestyles. Entomopathogenic nematodes (EPNs) are of great interest in agriculture because they vector insect pathogenic bacteria, which are capable of causing death to an insect host within 48 hours post-infection. Much of the molecular underpinnings in this system still remain to be discovered, from understanding the basic ability of these two organisms to associate with one another to genetically engineering more robust and host specific pathogens for application in the field. The focus of the research presented herein is on Steinernematidae nematodes and their bacterial symbionts. Specifically, it focused on the relationship between Xenorhabdus bovienii and its Steinernema hosts. Bioassays were designed to investigate insect virulence of X. bovienii alone in two Lepidoptera insect species with known differential susceptibility to Steinernema-Xenorhabdus pairs. A comparative genomic analysis was performed to compare different Xenorhabdus bovienii strains with observed variation in insect virulence. Results from this analysis demonstrated that virulent strains possess a type VI secretion system (T6SS) locus that is completely absent in strains with attenuated virulence. Bacterial competition assays between T6SS+ and T6SS- strains suggest this locus is involved in bacterial competition. Additionally, symbiont preference assays were carried out to investigate whether Steinernema hosts are able to discern between virulent and attenuated X. bovienii strains. Results from these assays revealed that Steinernema nematodes are able to distinguish between cognate and non-cognate X. bovienii symbionts, giving preference to virulent strains over those with attenuated virulence. Altogether these results provide further evidence that supports the notion that symbiont-switching events have occurred over the Steinernema-Xenorhabdus co-evolutionary history. Specifically, the competitive virulence of certain X. bovienii strains may have conferred them the ability to be selected by different Steinernema hosts, therefore contributing to the success of the nematode-bacterium partnership in being pathogenic to diverse insect hosts.en
dc.typetexten
dc.typeElectronic Thesisen
dc.subjectinsect virulenceen
dc.subjectSteinernemaen
dc.subjecttype VI secretion systemen
dc.subjectMicrobiologyen
dc.subjecthost-symbiont switchingen
thesis.degree.nameM.S.en
thesis.degree.levelmastersen
thesis.degree.disciplineGraduate Collegeen
thesis.degree.disciplineMicrobiologyen
thesis.degree.grantorUniversity of Arizonaen
dc.contributor.advisorStock, S. Patriciaen
dc.contributor.committeememberStock, S. Patriciaen
dc.contributor.committeememberMcCarthy, Fionaen
dc.contributor.committeememberVedantam, Gayatrien
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