title: Single-molecule study of molecular mobility in the cytoplasm of Escherichia coli.
abstract: The cytoplasm of bacterial cells is filled with individual molecules and molecular complexes that rely on diffusion to bring them together for interaction. The mobility of molecules in the cytoplasm has been characterized by several techniques mainly using fluorescent probes and ensemble methods. In order to probe the microenvrionment inside the cytoplasm as viewed by an individual molecule, we have studied single green fluorescent proteins (GFPs) diffusing in the cytoplasm of Escherichia coli cells at observation at rates ranging from 60 to 1000 Hz. Over long times the diffusion shows confinement due to the geometry of the cells themselves. A simulation in model cells using the actual distribution of cell sizes found in the experiments describes accurately the experimental results as well as reveals a short time diffusion coefficient that agrees well with that determined by ensemble methods. Higher short time diffusion coefficients can be obtained by filling the simulated cell with small spheres modeling cytoplasmic molecules and, depending on the density of particles included in the modeled cytoplasm, can approach the diffusion coefficient of GFPs found in water. Thus, single-molecule tracking combined with analysis using simple simulation of Brownian motion is able to reveal the main contributors to the GFP mobility in the cytoplasm of E. coli.
authors.affiliation: Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Yoriko
authors.initials: Y
authors.lastname: Lill
authors.forename: Wallace A
authors.initials: WA
authors.lastname: Kaserer
authors.forename: Salete M
authors.initials: SM
authors.lastname: Newton
authors.forename: Markus
authors.initials: M
authors.lastname: Lill
authors.forename: Phillip E
authors.initials: PE
authors.lastname: Klebba
authors.forename: Ken
authors.initials: K
authors.lastname: Ritchie
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004058:Diffusion; D048168:Escherichia coli K12 / Q000166:cytology* / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D009010:Monte Carlo Method; D009068:Movement
chemical_list: D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria; D049452:Green Fluorescent Proteins