Ultrastructure of the membrane systems in the unicellular cyanobacterium Synechocystis sp. strain PCC 6803 |
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Authors: | Michelle Liberton R Howard Berg John Heuser Robin Roth Himadri B Pakrasi |
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Institution: | (1) Department of Biology, Washington University, St. Louis, Missouri;(2) Donald Danforth Plant Science Center, St. Louis, Missouri;(3) Department of Cell Biology and Physiology, Washington University, St. Louis, Missouri |
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Abstract: | Summary. Among prokaryotes, cyanobacteria are unique in having highly differentiated internal membrane systems. Like other Gram-negative
bacteria, cyanobacteria such as Synechocystis sp. strain PCC 6803 have a cell envelope consisting of a plasma membrane, peptidoglycan layer, and outer membrane. In addition,
these organisms have an internal system of thylakoid membranes where the electron transfer reactions of photosynthesis and
respiration occur. A long-standing controversy concerning the cellular ultrastructures of these organisms has been whether
the thylakoid membranes exist inside the cell as separate compartments, or if they have physical continuity with the plasma
membrane. Advances in cellular preservation protocols as well as in image acquisition and manipulation techniques have facilitated
a new examination of this topic. We have used a combination of electron microscopy techniques, including freeze-etched as
well as freeze-substituted preparations, in conjunction with computer-aided image processing to generate highly detailed images
of the membrane systems in Synechocystis cells. We show that the thylakoid membranes are in fact physically discontinuous from the plasma membrane in this cyanobacterium.
Thylakoid membranes in Synechocystis sp. strain PCC 6803 thus represent bona fide intracellular organelles, the first example of such compartments in prokaryotic
cells.
Supplementary material to this paper is available in electronic form at
Correspondence and reprints: Department of Biology, CB1137, Washington University, St. Louis, MO 63130, U.S.A. |
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Keywords: | : Cyanobacteria Synechocystis sp Plasma membrane Thylakoid membrane |
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