New Methods in Electron Microscopy Help Elucidate the Structure of the Murein Sacculus and the Distribution of Penicillin-Binding Proteins
Since bacteria are so small (usually about 1.5–2.5 μm3), microbiologists have relied on microscopy to differentiate single bacteria from their neighbours, to determine cellular shape and form, to distinguish gram-negative cultures from gram-positive ones, and to detect the position of envelope adornments (e.g., flagella and capsules). These characteristics could usually be determined by light microscopy and it was not until the early 1950s that more detail was discovered by electron microscopy (Chapman and Hillier, 1953). The absence of a nucleus was confirmed, and the unequivocal detection of cell wall layers, and their contribution to cell division, outside a bilayered plasma membrane was established (Murray et al, 1965). These were halcyon days for microbial structure since electron microscopy was capable of discerning most of the structural bits and pieces which composed intact bacterial cells (Holt and Beveridge, 1982). Ribosomes and chromosomal DNA fibres could be discerned within the cytoplasm, and gram-positive and gram-negative bacteria could be distinguished by their cell envelope profiles. The former possessed an amorphous, electron dense wall above the plasma membrane, whereas the later possessed a more complex profile consisting of a thin peptidoglycan layer sandwiched between a plasma membrane and an outer membrane (Beveridge, 1981). Indeed, these early observations of envelope profiles by thin section firmly established the existence of a periplasmic space (i.e., a region encompassing or surrounding the cellular plasm) and, later, of Bayer’s so-called “adhesion zones” (Bayer, 1974) in gram-negative bacteria.
KeywordsOuter Membrane Periplasmic Space Substitution Medium Filament Terminus Thin Freeze Film
Unable to display preview. Download preview PDF.
- Amako, K., and Takade, A. (1985) The fine structure of Bacillus subtilis revealed by the rapid-freezing and subsitution-fixation method. J. Electron Microsc. 34,13–17.Google Scholar
- Beveridge, T.J. (1988b) Wall ultrastructure: how little we know, in “Antibiotic Inhibition of Bacterial cell Surface Assembly and Function” (Actor, P., Daneo-Moore, L., Higgins, M.L., Salton, M.R.J., and Shockman, G.D., eds.), p.3–20. Amer. Soc. Microbiol., Washington, D.C.Google Scholar
- Beveridge, T.J., Harris, R. and Humphrey, R. (1985) Evaluation of conventional and low temperature techniques for the preservation of bacterial structure. Proc. Micros. Soc. Can. 12, 22–23.Google Scholar
- Beveridge, T.J., Popkin, T.J. and Cole, R.M. (1992) Electron microscopy, in “Methods for General and Molecular Bacteriology” (Gerhardt, P., ed.), in press, Amer. Soc. Microbiol., Washington, D.C.Google Scholar
- Park, J.T. (1987) The murein sacculus, in “Escherichia coli and Salmonella typhimurium: Cellular and Molecular Biology” (Neidhardt, F.C., Ingraham, J.L., Low, K.B., Magasanik, B., Schaechter, M. and Umbarger, H.E., Eds.), pp. 23–30 Amer. Soc. Microbiol., Washington, D.C.Google Scholar
- Paul, T.R., Halligan, N.G., Blaszczak, L, Parr, T.R., Jr. and Beveridge, T.J. (1992a) A new mercury-penicillin V derivative as a probe for ultrastructural location of penicillin-binding proteins in Escherichia coli. J. Bacteriol. (in press).Google Scholar
- Paul, T.R., Beveridge, T.J., Halligan, N.G., Blaszczak, L.C. and Parr, T.R., Jr. (1992b) The use of a mercury penicillin derivative to localize penicillin-binding proteins in Escherichia coli, in “Bacterial Growth and Lysis: Metabolism and Structure of the Bacterial Sacculus” (de Pedro, M.A., Höltje, J.-V and Löffelhardt, W., eds). p. —. Plenum Pub. Corp., New York.Google Scholar
- Robards, A.W. and Sleytr, U.B. (1985) Low temperature methods in biological electron microscopy. Elsevier Biomewdical Press, Amsterdam.Google Scholar