The fine structure of <i>Sphaerotilus nutans</i>

Hoeniger, Judith F. M.; Tauschel, Horst-Dietmar; Stokes, J. L.

doi:10.1139/m73-051

Cited by 38 publications

(31 citation statements)

References 2 publications

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“…1), suggesting a relationship between the polar flagella and the polar organelle. Further supporting this model, Sphaerotilus natans swarm cells have a polar organelle, whereas nonmotile cells do not (34). The polar organelle has not been identified in all polarly flagellated bacteria, although it is possible that more subtle structures take on a similar role.…”

Section: Morphological Differences At Cell Endsmentioning

confidence: 83%

Polarity in Action: Asymmetric Protein Localization in Bacteria

2001

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Recent advances in microscopy and protein localization techniques have provided new insights into the remarkable complexity of the bacterial cell. Although bacteria lack discrete cellular compartments such as organelles, they possess an impressive scheme of subcellular organization at the level of protein localization. There are a growing number of examples of bacterial proteins for which specific intracellular localizations are essential for proper function and regulation. Dynamic polar localization of proteins critical for cell division, chromosome partitioning, and cell cycle control in Escherichia coli, Bacillus subtilis, and Caulobacter crescentus have recently been described (see Table 1). These exciting observations establish that bacterial polarity plays a critical cellular role and that prokaryotic organization is much more complex than previously believed.Clearly, many proteins and protein complexes are able to navigate the bacterial cell and ultimately recognize their appropriate destinations. The current challenge is to uncover the mechanisms, both active and passive, by which proteins are localized and then maintained at the proper intracellular location. The goal of this minireview is to explore a variety of examples of bacterial polarity, to expand upon the current models of polar localization, and to shed light on the spectrum of ways that bacteria may distinguish the polar cellular membrane from the lateral membrane. Several excellent reviews covering recent observations of dynamic polar protein localization have recently been published (7,37,38,41,76,82,83,92,93,102). Here we focus on other aspects of bacterial polarity, including the ultrastructural differences at the cell pole, the modes of polarity in actin-based motility and chemotaxis, and the implications of polarity in bacterial cellular function. MORPHOLOGICAL DIFFERENCES AT CELL ENDSThe diversity of bacterial shapes extends well beyond the basic sphere, rod, and spirochete forms. Many bacteria are decorated with pili, flagella, and/or stalks, which are often found exclusively at one or both cell poles. The presence of such polar structures reveals that at least some bacteria display a complicated organization scheme, since biogenesis of polar structures clearly demands an asymmetry of their components.In addition to these external polar structures, early ultrastructural studies revealed internal differences at the cell poles of some bacteria. One striking example is the polar organelle found at the flagellated pole of diverse gram-negative bacteria such as Aquaspirillum (65), Sphaerotilus (96), Rhodopseudomonas (95), Campylobacter (9, 75), and Helicobacter (63). In each case, the polar organelle is subpolarly located near the cytoplasmic membrane adjacent to the flagella (Fig. 1), suggesting a relationship between the polar flagella and the polar organelle. Further supporting this model, Sphaerotilus natans swarm cells have a polar organelle, whereas nonmotile cells do not (34). The polar organelle has not been identified in all polarl...

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Section: Morphological Differences At Cell Endsmentioning

confidence: 83%

Polarity in Action: Asymmetric Protein Localization in Bacteria

2001

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“…Superficially, the sheath of SP-6 is structurally and chemically similar to sheaths of S. natans (30,45) and cyanobacteria (4,31,43,47,56). The sheaths of these bacteria have all been reported to be composed of a random meshwork of fibrils that are rich in carbohydrate with lesser amounts of protein.…”

Section: Discussionmentioning

confidence: 96%

“…cells inside sheaths are protected from grazing by protozoa (17). Other Previous work has identified a general pattern in the structure and chemistry of the sheaths of Sphaerotilus natans (22,30,45) and a few filamentous cyanobacteria (4,31,43,46,47,56). These bacterial sheaths consist of a meshwork of polysaccharide-and protein-rich fibrils.…”

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confidence: 94%

Ultrastructure and chemical composition of the sheath of Leptothrix discophora SP-6

1993

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Light microscopy and transmission electron microscopy of thin sections and metal-shadowed specimens showed that the sheath of Leptothrix discophora SP-6 (ATCC 51168) is a tube-like extracellular polymeric structure consisting of a condensed fabric of 6.5-nm-diameter fibrils underlying a more diffuse outer capsular layer. In thin sections, outer membrane bridges seen to contact the inner sheath layer suggested that the sheath fabric was attached to the outer layer of the gram-negative cell wall. The capsular polymers showed an affinity for cationic colloidal iron and polycationic ferritin, indicating that they carry a negative charge. Cell-free sheaths were isolated by treatment with a mixture of lysozyme, EDTA, and N-lauroylsarcosine (Sarkosyl) or sodium dodecyl sulfate (SDS). Both Sarkosyl-and SDS-isolated sheaths were indistinguishable in microscopic appearance. However, the Mn-oxidizing activity of Sarkosyl-isolated sheaths was more stable than that of SDS-isolated sheaths. The Sarkosyl-isolated sheaths also contained more 2-keto-3-deoxyoctanoic acid and more outer membrane protein than SDS-isolated sheaths. The oven-dried mass of detergent-isolated sheaths represented approximately 9% of the total oven-dried biomass of SP-6 cultures; the oven-dried sheaths contained 38% C, 6.9%o N, 6% H, and 2.1% S and approximately 34 to 35% carbohydrate (polysaccharide), 23 to 25% protein, 8% lipid, and 4% inorganic ash. Gas-liquid chromatography showed that the polysaccharide was an approximately 1:1 mixture of uronic acids (glucuronic, galacturonic, and mannuronic acids and at least one other unidentified uronic acid) and an amino sugar (galactosamine). Neutral sugars were not detected.Amino acid analysis showed that sheath proteins were enriched in cysteine (6 mol%). The cysteine residues in the sheath proteins probably provide sulfhydryls for disulfide bonds that play an important role in maintaining the structural integrity of the sheath (D. Emerson and W. C. Ghiorse, J. Bacteriol. 175:7819-7827, 1993 (24,36,39).Leptothrix spp. are similar in physiology and cellular structure to closely related gram-negative aerobic heterotrophic pseudomonads (1, 2, 23, 55). Sheath formation and extracellular metal-oxidizing ability are the two major phenotypic criteria distinguishing them from closely related bacteria. The manganese-and iron-oxidizing activities of L. discophora SS-1 (ATCC 43182) are at least partly determined by metal-oxidizing proteins excreted by the cells in association with extracellular polymers (3, 10, 13). Presumably the excreted metaloxidizing proteins are associated with polymers located in the sheath. However, strain SS-1 irreversibly lost the ability to form a sheath soon after it was isolated (2). Recently we reported the isolation and maintenance of a new strain of L. discophora, SP-6 (ATCC 51168) (19). A sheathless variant, strain SP-6(sl) (ATCC 51169), also was isolated. Taxonomic studies (19,57) showed that strains SP-6 and SP-6(sl) are very similar but not identical to strain SS-1.

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“…These results confirm that the sheath fibrils consist of high-molecular-weight heteropolysaccharide-protein complexes. We hypothesize that proteins in the fibril complexes provide interfibril cross-linking to maintain the structural integrity of the sheath.Several previous studies of eubacterial sheaths have focused on their ultrastructure and gross chemical composition (1,20,31,33,34,42). These tube-like extracellular structures are composed principally of heteropolysaccharides in a fabric of fine fibrils, which appear to be the primary structural elements (11,20,31).…”

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confidence: 99%

“…These tube-like extracellular structures are composed principally of heteropolysaccharides in a fabric of fine fibrils, which appear to be the primary structural elements (11,20,31). Bacterial sheaths are very durable structures.…”

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confidence: 99%

Role of disulfide bonds in maintaining the structural integrity of the sheath of Leptothrix discophora SP-6

Emerson

Ghiorse

1993

J Bacteriol

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Isolated sheaths of Leptothrix discophora SP-6 (ATCC 51168) were tested for susceptibility to degradation by a variety of chemical denaturants and lytic enzymes and found to be resistant to many reagents and enzyme treatments. However, disulfide bond-reducing agents such as dithiothreitol (DTT), P-mercaptoethanol, sodium cyanide, and sodium sulfite degraded the sheath, especially at elevated pH (pH 9) and temperature (50°C). DTT and 1-mercaptoethanol caused more rapid degradation of the sheath than cyanide or sulfite. Treatment of the sheath with 1 N NaOH resulted in rapid breakdown, while treatment with 1 N HCI resulted in slow but significant hydrolysis. Transmission electron microscopy showed that the 6.5-nm fibrils previously shown to be an integral structural element of the sheath fabric (D. Emerson and W. C. Ghiorse, J. Bacteriol. 175:7808-7818, 1993) were progressively dissociated into random masses during DTT-induced degradation. Quantitation of disulfide bonds with DTT showed that the sheaths contained approximately 2.2 ,umol of disulfides per mg of sheath protein. Reaction with 5,5'-dithio-bis-(2-nitrobenzoic acid) showed that sheaths also contained approximately 0.8 ,umol of free sulfhydryls per mg of protein. A sulfhydryl-specific fluorescent probe (fluorescein 5-maleimide) showed that the free sulfhydryls in sheathed cell filaments were evenly distributed throughout the sheath. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis autoradiography of ['4C]iodoacetamide-labeled sheaths and DTT-dissociated sheath fibril suspensions showed that the majority of "4C-labeled sulfhydryls in the sheaths did not enter the gel. However, low-molecular-mass silver-staining bands (14 to 45 kDa) did appear in the gels after iodoacetic acid or iodoacetamide alkylation of the dissociated fibrils. These bands did not stain with Coomassie blue. Their migration in gels was slightly affected by digestion with pronase. The fibrils contained 20 to 25% protein. These results confirm that the sheath fibrils consist of high-molecular-weight heteropolysaccharide-protein complexes. We hypothesize that proteins in the fibril complexes provide interfibril cross-linking to maintain the structural integrity of the sheath.Several previous studies of eubacterial sheaths have focused on their ultrastructure and gross chemical composition (1,20,31,33,34,42). These tube-like extracellular structures are composed principally of heteropolysaccharides in a fabric of fine fibrils, which appear to be the primary structural elements (11,20,31). Bacterial sheaths are very durable structures. Indeed, fossilized eubacterial sheaths are frequently reported in the geologic record (17). It seems likely that covalent cross-linking could play a major role in maintaining the structure. However, the manner by which the macromolecular components of the sheath fabric are cross-linked has not been elucidated.In an accompanying paper (15), we show that the fine structure and gross chemical composition of the sheath of Leptothrix discophora SP-6 clos...

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The fine structure of Sphaerotilus nutans

Cited by 38 publications

References 2 publications

Polarity in Action: Asymmetric Protein Localization in Bacteria

Polarity in Action: Asymmetric Protein Localization in Bacteria

Ultrastructure and chemical composition of the sheath of Leptothrix discophora SP-6

Role of disulfide bonds in maintaining the structural integrity of the sheath of Leptothrix discophora SP-6

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