title: Signal processing and flagellar motor switching during phototaxis of Halobacterium salinarum.
abstract: Prokaryotic taxis, the active search of motile cells for the best environmental conditions, is one of the paradigms for signal transduction. The search algorithm implemented by the cellular biochemistry modulates the probability of switching the rotational direction of the flagellar motor, a nanomachine that propels prokaryotic cells. On the basis of the well-known biochemical mechanisms of chemotaxis in Escherichia coli, kinetic modeling of the events leading from chemoreceptor activation by ligand binding to the motility response has been performed with great success. In contrast to Escherichia coli, Halobacterium salinarum, in addition, responds to visible light, which is sensed through specific photoreceptors of different wavelength sensitivity (phototaxis). Light stimuli of defined intensity and time course can be controlled precisely, which facilitates input-output measurements used for system analysis of the molecular network connecting the sensory receptors to the flagellar motor switch. Here, we analyze the response of halobacterial cells to single and double-pulse light stimuli and present the first kinetic model for prokaryotic cells that couples the signal-transduction pathway with the flagellar motor switch. Modeling based on experimental data supports the current biochemical model of halobacterial phototaxis. Moreover, the simulations demonstrate that motor switching occurs through subsequent rate-limiting steps, which are both under sensory control, suggesting that two signals may be involved in halobacterial phototaxis.
authors.affiliation: Max-Planck-Institute for Dynamics of Complex Technical Systems, 39106 Magdeburg, Germany. torsten@mpi-magdeburg.mpg.de
authors.forename: Torsten
authors.initials: T
authors.lastname: Nutsch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Marwan
authors.forename: Dieter
authors.initials: D
authors.lastname: Oesterhelt
authors.forename: Ernst Dieter
authors.initials: ED
authors.lastname: Gilles
mesh_terms: D019843:Archaeal Proteins / Q000502:physiology; D002633:Chemotaxis / Q000502:physiology*; D003198:Computer Simulation; D005407:Flagella / Q000502:physiology*; D019617:Halobacterium salinarum / Q000502:physiology*; D008027:Light; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology; D020283:Photoreceptors, Microbial / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D013816:Thermodynamics
chemical_list: D019843:Archaeal Proteins; D020409:Molecular Motor Proteins; D020283:Photoreceptors, Microbial