High-resolution topography of the S-layer sheath of the archaebacterium Methanospirillum hungatei provided by scanning tunneling microscopy

Abstract

The inner and outer surfaces of the sheath of Methanospirillum hungatei GP1 have been imaged for the first time by using a bimorph scanning tunneling microscope (STM) on platinum-coated or uncoated specimens to a nominal resolution in height of ca. 0.4. nm. Unlike more usual types of microscopy (e.g., transmission electron microscopy), STM provided high-resolution topography of the surfaces, giving good depth detail which confirmed the sheath to be a paracrystalline structure possessing minute pores and therefore impervious to solutes possessing a hydrated radius of greater than 0.3 nm. STM also confirmed that the sheath consisted of a series of stacked hoops approximately 2.5 nm wide which were the remnants of the sheath after treatment with 2% (wt/vol) sodium dodecyl sulfate-2% (vol/vol) beta-mercaptoethanol (pH 9.0). No topographical infrastructure could be seen on the sides of the hoops. This research required the development of a new long-range STM capable of detecting small particles such as bacteria on graphite surfaces as well as a new "hopping" STM mode which did not deform the poorly conducting bacterial surface during high-resolution topographical analysis.