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Title: The distinct roles of Pseudomonas α-glucan and trehalose in desiccation and osmotic stress tolerances
Author: Woodcock, Stuart
ISNI:       0000 0004 8509 6514
Awarding Body: University of East Anglia
Current Institution: University of East Anglia
Date of Award: 2019
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Pseudomonas aeruginosa and Pseudomonas syringae are significant pathogens of humans and plants, respectively. 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 trehalose. 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 treS or treY/treZ operons, deletion of which reduces pathogenicity in planta, illustrating the importance of trehalose metabolism during plant infection. We used a combination of genetics and biochemistry to dissect trehalose metabolism. 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 responsible for the degradation of trehalose in Pseudomonas spp. forming the polysaccharide α-glucan. As expected, we found that trehalose was a key molecule during survival in osmotic conditions. An absence of intracellular trehalose yielded osmotically-sensitive strains, whereas those with increased levels of trehalose were osmotically-resistant. Surprisingly α-glucan conferred no discernable effect on osmotic sensitivity but was 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. Other groups have observed the upregulation of genes responsible for the production of the exopolysaccahride alginate during desiccation stress, in Pseudomonas spp. We showed that alginate is also involved in the protection against desiccation stress. Using Arabidopsis thaliana as an infection model, we observe attenuation when trehalose, α-glucan, and alginate biosynthetic pathways are absent, demonstrating importance of water stress during various stages of the Pseudomonas life cycle.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available