Biology subjects

Bornemann, S.

Publications and source records attributed to Bornemann, S..

2 recordsLinked to original sources

bioRxiv2020

Trehalose and α-glucan mediate distinct abiotic stress responses in Pseudomonas aeruginosa

An important prelude to bacterial infection is the ability of a pathogen to survive independently of the host and to withstand environmental stress. The compatible solute trehalose has previously been connected with diverse abiotic stress tolerances, particularly osmotic shock. In this study, we combine molecular biology and biochemistry to dissect the trehalose metabolic network in the opportunistic human pathogen Pseudomonas aeruginosa PA01 and define its role in abiotic stress protection. We show that trehalose metabolism in PA01 is integrated with the biosynthesis of branched -glucan (glycogen), with mutants in either biosynthetic pathway significantly compromised for survival on abiotic surfaces. While both trehalose and -glucan are important for abiotic stress tolerance, we show they counter distinct stresses. Trehalose is vital to the PA01 osmotic stress response, with trehalose synthesis mutants displaying severely compromised growth in elevated salt conditions. However, trehalose does not contribute directly to the PA01 desiccation response. Rather, desiccation tolerance is mediated directly by GlgE-derived -glucan, with deletion of the glgE synthase gene compromising PA01 survival in low humidity but having little effect on osmotic sensitivity. Desiccation tolerance is independent of trehalose concentration, marking a clear distinction between the roles of these two molecules in mediating responses to abiotic stress.

microbiology↗

bioRxiv2020

The molecular basis for a temperature-sensitive Mycobacterium smegmatis glgE mutant

BackgroundThe bacterial GlgE pathway is the third known route to glycogen and is the only one present in mycobacteria. It contributes to the virulence of Mycobacterium tuberculosis. The involvement of GlgE in glycogen biosynthesis was discovered twenty years ago when the phenotype of a temperature-sensitive Mycobacterium smegmatis mutation was rescued by the glgE gene. The evidence at the time suggested glgE coded for a glucanase responsible for the hydrolysis of glycogen, in stark contrast with recent evidence showing GlgE to be a polymerase responsible for its biosynthesis. MethodsWe reconstructed and examined the temperature-sensitive mutant and characterised the mutated GlgE enzyme. ResultsThe mutant strain accumulated the substrate for GlgE, -maltose-1-phosphate, at the non-permissive temperature. The glycogen assay used in the original study was shown to give a false positive result with -maltose-1-phosphate. The accumulation of -maltose-1-phosphate was due to the lowering of the kcat of GlgE as well as a loss of stability 42 {o}C. The reported rescue of the phenotype by GarA could potentially involve an interaction with GlgE, but none was detected. ConclusionsWe have been able to reconcile apparently contradictory observations and shed light on the basis for the phenotype of the temperature-sensitive mutation. General SignificanceThis study highlights how the lowering of flux through the GlgE pathway can slow the growth mycobacteria.

biochemistry↗