Stress-relieving sugars and bacterial pathogenesis

Lead Research Organisation: University of East Anglia
Department Name: Graduate Office

Abstract

This project will define the role of a-glucan in the pathogenic species Pseudomonas aeruginosa and Pseudomonas syringae. We have recently identified the GlgE metabolic pathway that contributes to the biosynthesis of capsular a-glucan, a novel exopolysaccharide that coats the surface of mycobacteria and plays an important role in human immune evasion. The glgE pathway genes are widespread, occurring in 14% of all sequenced bacterial genomes including the important plant and human pathogens P. syringae and P. aeruginosa. However the role of a-glucans in organisms other than mycobacteria is currently unknown. Based on our research to date, we propose that GlgE a-glucan contributes to the tolerance of Pseudomonas species to specific environmental stresses. In this way, the Pseudomonas glgE pathway potentially impacts both bacterial survival, infection and pathogenicity. The student will use a combination of bacterial genetics, biochemistry and plant pathogenesis to study the role that a-glucan plays in stress tolerance, particularly in the context of biofilm formation and plant infection. This is a joint proposal between researchers at two world-renowned research institutes; the John Innes Centre and the Sainsbury Laboratory in Norwich, UK. The results of this project will be relevant both in the context of plant pathogenicity, and also to our understanding of opportunistic human infection.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
BB/M011216/1 01/10/2015 30/09/2023
1654200 Studentship BB/M011216/1 01/10/2015 30/09/2019 Stuart Woodcock
 
Description Pseudomonas aeruginosa and Pseudomonas syringae are significant pathogens of humans and plants, respectively, and infections are difficult to treat. An important prelude to infection is the ability of the pathogen to survive independently of the host and to withstand environmental stresses. This is achieved through several mechanisms, including the biosynthesis of the disaccharide trehalose. The production of trehalose has previously been implicated in the tolerance of a wide range of abiotic stresses, particularly osmotic shock. Trehalose biosynthetic enzymes in Pseudomonas spp. were thought to be encoded by the TreY/TreZ and TreS operons. Deletion of these operons reduces pathogenicity in planta, illustrating the importance of trehalose metabolism during plant infection.

We used a combination of genetics and biochemistry to dissect the biosynthesis and degradation of trehalose. This work has allowed us to examine the relationship between the biosynthesis of this molecule, and its roles in stress protection. Contrary to previous understanding, we show that the TreS operon is in fact responsible for the degradation of trehalose in Pseudomonas spp. forming the polysaccharide a-glucan. As expected we found that trehalose was a key molecule during survival in osmotic conditions. Absence of intracellular trehalose yielded osmotically sensitive strains, whereas those which accumulated increased levels of trehalose showed increased resistance to osmotic stress. Surprisingly a-glucan conferred no discernable effect on osmotic sensitivity but was shown to be highly important for survival under desiccating conditions. This phenotype was independent of the level of trehalose, marking a clear distinction between the roles of these two molecules in plant interactions and infection.

During desiccation stress, other groups have observed the up-regulation of genes responsible for the production of the exo-polysaccahride alginate in Pseudomonas spp. We disrupted alginate biosynthesis in both P. aerguinosa and P. syringae and show that alginate is also involved in the protection against desiccation stress. Using Arabidopsis thaliana as an infection model for P. syringae infection we do not observe any difference in the course of infection when bacteria lack biosynthetic genes for glucan, trehalose or alginate. However, when all three biosynthesis pathways are absent, pathogenicity is attenuated. This shows the importance of water stress during various stages of the bacterial life cycle.
Exploitation Route Bacteria in the environment present a potential reservoir of infectious innocula, this work increases our understanding of how bacteria survive, and potentially how to prevent infection from these sources. This work may also have applications in protecting crop plants from drought stress.
Sectors Agriculture, Food and Drink,Environment,Healthcare,Pharmaceuticals and Medical Biotechnology

 
Description Biochemical Society General Travel Grant
Amount £400 (GBP)
Organisation Biochemical Society 
Sector Learned Society
Country United Kingdom
Start 09/2017 
End 09/2017
 
Description JIC 50 Open Day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact JIC open day to celebrate 50th anniversary in Norwich.
Year(s) Of Engagement Activity 2017