Dissertation
The roles of nutrient stress in promoting surface colonization by Vibrio parahaemolyticus
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2019
DOI: 10.17077/etd.005184
Abstract
For bacteria versatile enough to thrive in the environment and in a host, the ability to deal with change is essential for survival. Vibrio parahaemolyticus, a marine and estuarine bacterium, pathogen of marine animals, and the leading cause of seafood associated gastroenteritis, is an example of a bacterium that has taken up the challenge with vigor. In liquid, V. parahaemolyticus is propelled at high speed by a single polar flagellum. On surfaces, transcription in Vibrio parahaemolyticus is drastically reprogrammed leading to a gene expression profile primed for colonization, including the hyperproduction of peritrichous lateral flagella that allow for robust swarming motility on surfaces or highly viscous media. Swarmer cell differentiation is an energetically costly endeavor and multiple layers of regulation exist to prevent unnecessary induction of surface colonization program.
Signals implicated in the environmental regulation of swarmer cell differentiation include iron limitation and inhibition of the polar flagellum. In this work, I showed that bacteria experience iron starvation more dramatically on surfaces than in liquid. I demonstrated that limitation of the essential but biologically unavailable nutrient iron affects swarmer cell differentiation via the conserved ferric uptake regulator protein, Fur. I described a new Fur-controlled regulator, FcrX, that diminishes the ability of Fur to repress its regulon. I determined that FcrX directly interacts with Fur.
A fur fla strain does not constitutively express laf genes, despite being insensitive to available iron and polar flagellar signaling. Growing this strain in increasingly dilute media induced lateral flagellar gene expression at incrementally earlier times. The accelerated induction of laf transcription was not a result of changes in cyclic-di-GMP, a second messenger known to affect laf expression. Manipulating the levels of the stringent response alarmone, ppGpp, I showed that accumulation of ppGpp induced laf expression. I further demonstrated that reducing the levels of ppGpp by deleting the gene encoding the major ppGpp synthetase RelA delayed laf expression. This indicated that the stringent response plays a role in tying regulation of the swarmer cell program with nutritional stress.
Iron and amino acid starvation are two resource limitations that a bacterium might face as environments change. The ability to escape depleted circumstances via upregulation of a surface motility program may provide a distinct survival advantage for these organisms.
Details
- Title: Subtitle
- The roles of nutrient stress in promoting surface colonization by Vibrio parahaemolyticus
- Creators
- Maria Liana Laserna Morabe
- Contributors
- Linda McCarter (Advisor)Craig Ellermeier (Committee Member)Bradley Jones (Committee Member)David Weiss (Committee Member)Jeffrey Banas (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Microbiology
- Date degree season
- Autumn 2019
- DOI
- 10.17077/etd.005184
- Publisher
- University of Iowa
- Number of pages
- xiii, 105 pages
- Copyright
- Copyright 2019 Maria Liana Laserna Morabe
- Language
- English
- Description illustrations
- illustrations
- Description bibliographic
- Includes bibliographical references (pages 93-102).
- Public Abstract (ETD)
A vast and microscopic biomass exists on the surfaces of the world around us. Many human interactions with bacteria are with surface-attached organisms. While the predominance of surface-associated bacteria has been known for a long time, our understanding of many aspects of surface colonization is still in progress. My work has focused on one facet of the complex phenomenon of surface-associated bacteria: signals for engaging the surface colonization program of bacteria, specifically surface motility.
Vibrio parahaemolyticus, the leading cause of seafood-associated gastroenteritis, is a marine and estuarine bacterium with a highly adaptable lifestyle. V. parahaemolyticus is incredibly motile. In its free-swimming state, motility is driven by a powerful polar flagellum, which can propel the bacterium at speeds of ~100 μm/s. Even with this strong propeller, the polar flagellum is unsuitable for translocation on surfaces. On surfaces, the lateral flagellar system of V. parahaemolyticus is induced resulting in production of multitudes of peritrichous lateral flagella. Differentiated swarmer cells are primed for surface motility and colonization. My thesis focuses on understanding how environmental signals, particularly iron and nutritional stress, affect this regulatory switch.
In this work, I show that the iron homeostasis regulator, Fur, represses the swarming program. I also discovered a new protein, FcrX, that modulates Fur repression by interacting directly with Fur. I show that swarmer cell differentiation is regulated by nutritional stress via the stringent response alarmones (p)ppGpp. My work adds to our understanding of how nutritional signals are integrated with environmental circumstances to affect surface colonization and survival.
- Academic Unit
- Microbiology and Immunology
- Record Identifier
- 9983779398102771
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