Biology subjects

Schiessl, K.

Publications and source records attributed to Schiessl, K..

3 recordsLinked to original sources

bioRxiv2016

Benefits of siderophore release lie in mediating diffusion limitation at low iron solubility

Siderophores are chelators released by many bacteria to take up iron. In contrast to iron receptors located at the cell surface, released siderophores are at risk of being lost to environmental sinks. Here, we asked the question whether the release itself is essential for the function of siderophores, which could explain why such a risky strategy is widespread. We developed a reaction-diffusion model to determine the impact of siderophore release on overcoming iron limitation caused by poor solubility in aerobic, pH-neutral environments. We found that secretion of siderophores can efficiently accelerate iron uptake at low solubility, since secreted siderophores solubilize slowly diffusing large iron aggregates to small, quickly diffusing iron-siderophore complexes. At high iron solubility, however, when the iron-siderophore complex is no longer considerably smaller than the iron source itself, siderophore secretion can also slow down iron uptake. In addition, we found that cells can synergistically share their siderophores, depending on their distance and the level of iron aggregation. Overall, our study helps understand why siderophore secretion is so widespread: Even though a large fraction of secreted siderophores is lost, the solubilization of iron through secreted siderophores can efficiently increase iron uptake, especially if siderophores are produced cooperatively by several cells.

microbiology↗

bioRxiv2016

Individual- versus group-optimality in the production of secreted bacterial compounds

How unicellular organisms optimize the production of compounds is a fundamental biological question. While it is typically thought that production is optimized at the individual-cell level, secreted compounds could also allow for optimization at the group level, leading to a division of labor where a subset of cells produces and shares the compound with everyone. Using mathematical modelling, we show that the evolution of such division of labor depends on the cost function of compound production. Specifically, for any trait with saturating benefits, linear costs promote the evolution of uniform production levels across cells. Conversely, production costs that diminish with higher output levels favor the evolution of specialization - especially when compound shareability is high. When experimentally testing these predictions with pyoverdine, a secreted iron-scavenging compound produced by Pseudomonas aeruginosa, we found linear costs and, consistent with our model, detected uniform pyoverdine production levels across cells. We conclude that for shared compounds with saturating benefits, the evolution of division of labor is facilitated by a diminishing cost function. More generally, we note that shifts in the level of selection from individuals to groups do not solely require cooperation, but critically depend on mechanistic factors, including the distribution of compound synthesis costs.

evolutionary biology↗

bioRxiv2016

Magnitude and mechanism of siderophore-mediated competition in bacterial interactions

Whether microbial interactions are predominantly cooperative or competitive is a central question in microbial ecology, and determines the composition and stability of microbial communities. The secretion of iron chelators called siderophores is a model system for cooperative interactions, even though these chelators can also mediate competition by depriving competitors of iron. Using a genetically engineered experimental system based on the Pseudomonas aeruginosa siderophore pyochelin, we found that secreting siderophores to inhibit a competitor can lead to higher benefits than secreting siderophores to make iron available. Based on thermodynamic modeling, we propose that competitive inhibition by siderophores is efficient in kinetically controlled saturated systems, where dissolution of precipitated iron phases is slow. Under these conditions, met in many natural environments, secreted siderophores temporarily reduce the concentration of available iron and can thus induce growth inhibition in a competing strain, even at high iron concentrations. These findings give insight into the function of siderophores: In addition to its cooperative nature, siderophore secretion could also be a widespread mechanism for mediating competitive interactions. Our functional investigation reveals a complexity in microbial interaction networks that would remain hidden when focusing on genomic information alone.

microbiology↗