MODELING AND MEASURING THE ELASTIC PROPERTIES OF AN ARCHAEAL SURFACE,THE SHEATH OF METHANOSPIRILLUM-HUNGATEI, AND THE IMPLICATION FOR METHANE PRODUCTION

We describe a technique for probing the elastic properties of biologic al membranes by using an atomic force microscope (AFM) tip to press th e biological material into a groove in a solid surface. A simple model is developed to relate th applied force and observed depression dista nce to the elastic modulus of the material. A measurement on the prote inaceous sheath of the archaebacterium Methanospirillum hungatei GP1 g ave a Young's modulus of 2 x 10(10) to 4 x 10(10) N/m(2). The measurem ents suggested that the maximum sustainable tension in the sheath was 3.5 to 5 N/m. This finding implied a maximum possible internal pressur e for the bacterium of between 300 and 400 atm. Since the cell membran e and S-layer (wall) which surround each cell should be freely permeab le to methane and since we demonstrate that the sheath undergoes creep (expansion) with pressure increase, it is possible that the sheath ac ts as a pressure regulator by stretching, allowing the gas to escape o nly after a certain pressure is reached. This creep would increase the permeability of the sheath to diffusible substances.