title: Modelling and analysis of bacterial tracks suggest an active reorientation mechanism in Rhodobacter sphaeroides.
abstract: Most free-swimming bacteria move in approximately straight lines, interspersed with random reorientation phases. A key open question concerns varying mechanisms by which reorientation occurs. We combine mathematical modelling with analysis of a large tracking dataset to study the poorly understood reorientation mechanism in the monoflagellate species Rhodobacter sphaeroides. The flagellum on this species rotates counterclockwise to propel the bacterium, periodically ceasing rotation to enable reorientation. When rotation restarts the cell body usually points in a new direction. It has been assumed that the new direction is simply the result of Brownian rotation. We consider three variants of a self-propelled particle model of bacterial motility. The first considers rotational diffusion only, corresponding to a non-chemotactic mutant strain. Two further models incorporate stochastic reorientations, describing 'run-and-tumble' motility. We derive expressions for key summary statistics and simulate each model using a stochastic computational algorithm. We also discuss the effect of cell geometry on rotational diffusion. Working with a previously published tracking dataset, we compare predictions of the models with data on individual stopping events in R. sphaeroides. This provides strong evidence that this species undergoes some form of active reorientation rather than simple reorientation by Brownian rotation.
authors.affiliation: Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG, UK Department of Civil, Environmental and Geomatic Engineering, Faculty of Engineering Science, University College London, Chadwick Building, Gower Street, London WC1E 6BT, UK.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Rosser
authors.affiliation: Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG, UK.
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Baker
authors.affiliation: Oxford Centre for Integrative Systems Biology and Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Judith P
authors.initials: JP
authors.lastname: Armitage
authors.affiliation: Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Andrew Wiles Building, Radcliffe Observatory Quarter, Woodstock Road, Oxford OX2 6GG, UK alexander.fletcher@maths.ox.ac.uk.
authors.forename: Alexander G
authors.initials: AG
authors.lastname: Fletcher
mesh_terms: D016764:Cell Polarity / Q000502:physiology; D003198:Computer Simulation; D040542:Mechanotransduction, Cellular / Q000502:physiology*; D008954:Models, Biological; D009949:Orientation / Q000502:physiology*; D012212:Rheology / Q000379:methods; D012242:Rhodobacter sphaeroides / Q000166:cytology* / Q000502:physiology*; D012399:Rotation; D013314:Stress, Mechanical; D014783:Viscosity
keywords: Brownian motion; bacterial motility; rotational diffusion; self-propelled particle; tracking