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J. Bacteriol., 06 1996, 3106-3112, Vol 178, No. 11
W Xu, PJ Mulhern, BL Blackford, MH Jericho, M Firtel and TJ Beveridge
We describe a technique for probing the elastic properties of biological
membranes by using an atomic force microscope (AFM) tip to press the
biological material into a groove in a solid surface. A simple model is
developed to relate the applied force and observed depression distance to
the elastic modulus of the material. A measurement on the proteinaceous
sheath of the archaebacterium Methanospirillum hungatei GP1 gave a Young's
modulus of 2 x 10(10) to 4 x 10(10) N/m2. The measurements suggested that
the maximum sustainable tension in the sheath was 3.5 to 5 N/m. This
finding implied a maximum possible internal pressure for the bacterium of
between 300 and 400 atm. Since the cell membrane and S-layer (wall) which
surround each cell should be freely permeable to methane and since we
demonstrate that the sheath undergoes creep (expansion) with pressure
increase, it is possible that the sheath acts as a pressure regulator by
stretching, allowing the gas to escape only after a certain pressure is
reached. This creep would increase the permeability of the sheath to
diffusible substances.
Copyright © 1996, American Society for Microbiology
Modeling and measuring the elastic properties of an archaeal surface, the sheath of Methanospirillum hungatei, and the implication of methane production
Physics Department, Dalhousie University, Halifax, Nova Scotia, Canada.
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