Potential Mechanisms of Direct Competition Among Horizontally Transmitted Insect Symbionts Público

Abstract

Effective transmission is essential to the persistence of microbial symbioses that confer critical fitness advantages to their hosts. Contrasting to the direct methods of passage used by some partnerships, many symbioses depend on environmental transmission which hypothetically increases the potential for disruptions. Although the host organism has been demonstrated to impose mechanisms that filter out nonsymbiotic, environmental microbes, this is not fully sufficient to ensure the high-fidelity transmission dynamics that are observed. We hypothesize that horizontal symbiont transmission further depends on competitive dynamics between symbiont candidates. This was examined using the horizontally transmitted symbiosis between the squash bug Anasa tristis and its primary symbiont from the genus Caballeronia. The external culturability of Caballeronia enabled an extensive in vitro investigation into competitive dynamics between Caballeronia isolates. We first provide strong evidence of contact-dependent inhibition between a cohort of phylogenetically representative Caballeronia strains. This inhibition is strongly environmentally dependent. However, the Caballeronia strains do not demonstrate in vitro contact-dependent inhibition, which may be attributed to the highly regulated expression of the associated mechanisms that may require host conditions . We attempt to address this point by starting to create an in vivo model for competition by creating a Caballeronia mutant that is unable to compete through a known contact-dependent mechanism. Overall, this work provides a foundation for understanding how microbial symbionts ensure their passage and the evolutionary development of horizontal transmission. 

Table of Contents

Background.……………………………………………………………………………………...........1

Chapter 1: Contact Independent Caballeronia Strain Inhibition.……………………………6

Introduction……………………………………………………………………………………6

Methods…………………………………………………………………………………………7

Results…………………………………………………………………………………………10

Discussion…………………………………………………………………………………….13

Supplemental Figures……………………………………………………………………...17

Chapter 2: Contact-Dependent Caballeronia Strain Inhibition……………………………..19

Introduction………………………………………………………………………………....19

Methods……………………………………………………………………………………….20

Results…………………………………………………………………………………………23

Discussion…………………………………………………………………………………….26

Supplemental Figures………………………………………………………………………31

Chapter 3: Constructing Caballeronia T6SS KOs for in vivo Competition Assays……….34

Introduction………………………………………………………………………………….34

Methods……………………………………………………………………………………….35

Results…………………………………………………………………………………………40

Discussion…………………………………………………………………………………….45

Conclusions……………………………………………………………………………………...........50

References………………………………………………………………………………………..........53

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Biology, Microbiology Biology, Ecology Biology, General
Palabra Clave	Symbiosis Caballeronia Microbial Competition
Committee Chair / Thesis Advisor	Nic Vega, Emory University
Committee Members	Kathleen Campbell, Emory University Tim Read, Emory University Nicole Gerardo, Emory University

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