The three-dimensional structure of the cyanobacterium Synechocystis sp. PCC 6803

Abstract

To advance our knowledge of the model cyanobacterium Synechocystis sp. PCC 6803 we investigated the three-dimensional organization of the cytoplasm using standard transmission electron microscopy and electron tomography. Electron tomography allows a resolution of ~5 nm in all three dimensions, superior to the resolution of most traditional electron microscopy, which is often limited in part by the thickness of the section (70 nm). The thylakoid membrane pairs formed layered sheets that followed the periphery of the cell and converged at various sites near the cytoplasmic membrane. At some of these sites, the margins of thylakoid membranes associated closely along the external surface of rod-like structures termed thylakoid centers, which sometimes traversed nearly the entire periphery of the cell. The thylakoid membranes surrounded the central cytoplasm that contained inclusions such as ribosomes and carboxysomes. Lipid bodies were dispersed throughout the peripheral cytoplasm and often juxtaposed with cytoplasmic and thylakoid membranes suggesting involvement in thylakoid maintenance or biogenesis. Ribosomes were numerous and mainly located throughout the central cytoplasm with some associated with thylakoid and cytoplasmic membranes. Some ribosomes were attached along internal unit-membrane-like sheets located in the central cytoplasm and appeared to be continuous with existing thylakoid membranes. These results present a detailed analysis of the structure of Synechocystis sp. PCC 6803 using high-resolution bioimaging techniques and will allow future evaluation and comparison with gene-deletion mutants.

Photosynthetic Pigment Localization and Thylakoid Membrane Morphology Are Altered in Synechocystis 6803 Phycobilisome Mutants

“…In wild-type cells, PBS, PSII, and PSI are generally colocalized. The morphology of these spectral components has similarity to the TEM image shown in Figure 2A and elsewhere (Liberton et al, 2006;van de Meene et al, 2006), where the thylakoid membranes follow the cell periphery or can span the central cytoplasm. There are regions of PSII and PBS enrichment compared with PSI that are highlighted in the red-green composite images (Fig.…”

“…Progress has been made in understanding the supramolecular organization of these complexes in the thylakoid membrane of plants (for review, see Dekker and Boekema, 2005), where PSI and PSII are organized into so-called supercomplexes and are spatially separated in the stroma lamellae and grana stacks, respectively. However, this is not the case for cyanobacteria, where stroma lamellae and grana stacks are absent (Liberton et al, 2006;van de Meene et al, 2006).…”

“…In wild-type Synechocystis 6803 cells, thylakoid membranes are generally arranged as concentric layers that tend to follow the curvature of the plasma membrane, so that the central cytoplasmic region of the cell is largely devoid of thylakoids ( Fig. 2A; Liberton et al, 2006;van de Meene et al, 2006). Furthermore, when thylakoids are present in the cell interior, they often form arching loops of membrane layers (Mullineaux, 1999;Liberton et al, 2006).…”

“…Synechocystis 6803 are spherical cells of approximately 1.5 to 2 mm in diameter that have been extensively studied by electron microscopy, so their intracellular organization is well characterized (Liberton et al, 2006;van de Meene et al, 2006). These cells have thylakoid membranes organized primarily as three or more concentric layers around the cell periphery, with a central cytoplasmic region largely devoid of thylakoid membranes.…”

Lateral Segregation of Photosystem I in Cyanobacterial Thylakoids

“…Finally, these 3D-SIM images show that PSI-YFP is present in all areas of the thylakoid membrane; low concentrations of PSI are indicated by the blue signal, which traces the outlines of paired thylakoids as they traverse the cell and also shows points where they appear to converge ( Figure 9B, bottom left panel). These features have also been seen in tomographic reconstructions from negative stain electron microscopy (van de Meene et al, 2006).…”