title: Dual biochemical oscillators may control cellular reversals in Myxococcus xanthus.
abstract: Myxococcus xanthus is a Gram-negative, soil-dwelling bacterium that glides on surfaces, reversing direction approximately once every 6 min. Motility in M. xanthus is governed by the Che-like Frz pathway and the Ras-like Mgl pathway, which together cause the cell to oscillate back and forth. Previously, Igoshin et al. (2004) suggested that the cellular oscillations are caused by cyclic changes in concentration of active Frz proteins that govern motility. In this study, we present a computational model that integrates both the Frz and Mgl pathways, and whose downstream components can be read as motor activity governing cellular reversals. This model faithfully reproduces wildtype and mutant behaviors by simulating individual protein knockouts. In addition, the model can be used to examine the impact of contact stimuli on cellular reversals. The basic model construction relies on the presence of two nested feedback circuits, which prompted us to reexamine the behavior of M. xanthus cells. We performed experiments to test the model, and this cell analysis challenges previous assumptions of 30 to 60 min reversal periods in frzCD, frzF, frzE, and frzZ mutants. We demonstrate that this average reversal period is an artifact of the method employed to record reversal data, and that in the absence of signal from the Frz pathway, Mgl components can occasionally reverse the cell near wildtype periodicity, but frz- cells are otherwise in a long nonoscillating state.
authors.affiliation: University of California, Berkeley/University of California, San Francisco Joint Medical Program, Berkeley, California; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California.
authors.forename: Erik
authors.initials: E
authors.lastname: Eckhert
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California.
authors.forename: Padmini
authors.initials: P
authors.lastname: Rangamani
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California.
authors.forename: Annie E
authors.initials: AE
authors.lastname: Davis
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California.
authors.forename: George
authors.initials: G
authors.lastname: Oster
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, California; Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California; Department of Biology, St. Mary's College, Moraga, California. Electronic address: jeb8@stmarys-ca.edu.
authors.forename: James E
authors.initials: JE
authors.lastname: Berleman
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D055786:Gene Knockout Techniques; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D016941:Myxococcus xanthus / Q000166:cytology* / Q000378:metabolism*; D010641:Phenotype
chemical_list: D001426:Bacterial Proteins