Transient dynamic phenotypes as criteria for model discrimination: Fold-change detection in Rhodobacter sphaeroides chemotaxis

Abstract

The chemotaxis pathway of the bacterium Rhodobacter sphaeroides shares many similaritieswith that of Escherichia coli. It exhibits robust adaptation and has several homologues of the latter's chemotaxis proteins. Recent theoretical results have correctly predicted that the E. coli output behaviour is unchanged under scaling of its ligand input signal; this property is knownas fold-change detection (FCD). In the light of recent experimental results suggesting that R. sphaeroides may also show FCD, we present theoretical assumptions on the R. sphaeroides chemosensory dynamics that can be shown to yield FCD behaviour. Furthermore, it is shown that these assumptions make FCD a property of this system that is robust to structural and parametric variations in the chemotaxis pathway, in agreementwith experimental results.We construct and examinemodels of the full chemotaxis pathway that satisfy these assumptions and reproduce experimental time-series data from earlier studies. We then propose experiments in whichmodels satisfying our theoretical assumptions predict robust FCD behaviour where earliermodels do not. In thisway,we illustrate howtransient dynamic phenotypes such as FCD can be used for the purposes of discriminating between models that reproduce the same experimental time-series data. © 2013 The Authors.