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Iron Homeostasis in Bacterial Plant Colonization and Disease

Project Description

Background: Iron is an essential nutrient in all orders of life. Since uptake is hampered by insolubility, plants and bacteria have evolved mechanisms for active sequestration, through the secretion of chelators called siderophores, and uptake via transport mechanisms. As iron is a reactive metal, high concentrations within the cell can result in toxicity through the generation of reactive oxygen species (ROS) by the Fenton reaction. Owing to this, iron homeostasis needs to be tightly controlled.
In E. coli, the iron dependent transcriptional regulator fur regulates genes involved in iron metabolism, as well as tolerance to acid and oxidative stresses (McHugh et al 2003). E. coli K-12 has nine iron transport systems but pathogenic E. coli isolates have as many as 14 (Fig.1, adapted from Yep et al 2014). It has been hypothesised that this functional redundancy is required for pathogenicity and niche specificity.
Plants are dependent upon iron for many important functions such as photosynthesis, cell wall maintenance and stress responses, including defense against pathogens (ROS response).
The increase in incidence of foodborne outbreaks in association with fresh produce requires investigation into the fundamental interactions between these pathogens and their plant hosts. Preliminary data show that verotoxigenic E. coli O157:H7 Sakai (VTEC) differentially regulate iron transport and iron storage upon exposure to plant apoplastic washings in vitro. Upon exposure to spinach apoplast, nearly all iron transport and siderophore genes are significantly downregulated while ferritin is upregulated indicating high iron availability. In contrast, an iron transport system present only in pathogenic E. coli was significantly upregulated in response to apoplast from Nicotiana benthamiana. Understanding how VTEC adapts to the plant host environment can inform on food safety risk assessments and the plant defence response to bacterial colonisation.
Aims/Objectives: The aim of this project is to investigate the role of iron homeostasis in E. coli O157:H7 colonisation of plant hosts. The objectives of this project are to:
1. Determine which VTEC iron dependent systems respond to iron availability in the plant host, e.g. for metabolism and survival. Do the transcriptional responses measured in vitro correlate to responses from bacteria colonising the plant apoplast?
2. Determine the role of VTEC iron regulation in relation to the plant innate immune response.

Funding Notes

The studentship is funded under the James Hutton Institute/University Joint PhD programme, in this case with the University of Reading. Applicants should have a first-class honours degree in a relevant subject or a 2.1 honours degree plus Masters (or equivalent).Shortlisted candidates will be interviewed in Jan/Feb 2020. A more detailed plan of the studentship is available to candidates upon application. Funding is available for European applications.

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