title: Measuring the Viscosity of the Escherichia coli Plasma Membrane Using Molecular Rotors.
abstract: The viscosity is a highly important parameter within the cell membrane, affecting the diffusion of small molecules and, hence, controlling the rates of intracellular reactions. There is significant interest in the direct, quantitative assessment of membrane viscosity. Here we report the use of fluorescence lifetime imaging microscopy of the molecular rotor BODIPY C10 in the membranes of live Escherichia coli bacteria to permit direct quantification of the viscosity. Using this approach, we investigated the viscosity in live E. coli cells, spheroplasts, and liposomes made from E. coli membrane extracts. For live cells and spheroplasts, the viscosity was measured at both room temperature (23°C) and the E. coli growth temperature (37°C), while the membrane extract liposomes were studied over a range of measurement temperatures (5-40°C). At 37°C, we recorded a membrane viscosity in live E. coli cells of 950 cP, which is considerably higher than that previously observed in other live cell membranes (e.g., eukaryotic cells, membranes of Bacillus vegetative cells). Interestingly, this indicates that E. coli cells exhibit a high degree of lipid ordering within their liquid-phase plasma membranes.
authors.affiliation: Centre of Microbial and Plant Genetics (CMPG), KU Leuven, Leuven, Belgium. Electronic address: jacek.mika@chem.kuleuven.be.
authors.forename: Jacek T
authors.initials: JT
authors.lastname: Mika
authors.affiliation: Department of Chemistry, Imperial College London, London, United Kingdom.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Thompson
authors.affiliation: Department of Chemistry, Imperial College London, London, United Kingdom.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Dent
authors.affiliation: Department of Chemistry, Imperial College London, London, United Kingdom.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Brooks
authors.affiliation: Centre of Microbial and Plant Genetics (CMPG), KU Leuven, Leuven, Belgium.
authors.forename: Jan
authors.initials: J
authors.lastname: Michiels
authors.affiliation: Centre of Microbial and Plant Genetics (CMPG), KU Leuven, Leuven, Belgium.
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.affiliation: Department of Chemistry, Imperial College London, London, United Kingdom. Electronic address: m.kuimova@imperial.ac.uk.
authors.forename: Marina K
authors.initials: MK
authors.lastname: Kuimova
mesh_terms: D000465:Algorithms; D001896:Boron Compounds; D002462:Cell Membrane / Q000737:chemistry* / Q000378:metabolism; D004058:Diffusion; D004926:Escherichia coli; D005456:Fluorescent Dyes; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D018613:Microscopy, Confocal / Q000379:methods; D008856:Microscopy, Fluorescence / Q000379:methods*; D008954:Models, Biological; D013104:Spheroplasts / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D014783:Viscosity
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D005456:Fluorescent Dyes; D008081:Liposomes