The distinct roles of Pseudomonas α-glucan and trehalose in desiccation and osmotic stress tolerances

Woodcock, Stuart (2019) The distinct roles of Pseudomonas α-glucan and trehalose in desiccation and osmotic stress tolerances. Doctoral thesis, University of East Anglia.

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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.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Katherine Whittaker
Date Deposited: 14 Feb 2020 09:52
Last Modified: 14 Feb 2020 09:52


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