Biochemical Aspects of Extreme Halophilism

Larsen, Helge

doi:10.1016/s0065-2911(08)60251-9

Cited by 236 publications

(98 citation statements)

References 61 publications

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“…2 ) . This structure presumably relates to the pattern of hexagonally arranged pebble-like structures observed in shadowed preparations of halobacteria (Larsen, 1967). In sections of H. salinarium strain I the dented appearance of the surface was not so clearly recognizable ("1.…”

Section: Resultsmentioning

confidence: 97%

“…) and Cho, Doy & Mercer (1967) showed with improved techniques for electron microscopy that the anatomy of the cell envelope of Halobacterium halobium is more complex than indicated by earlier studies (Larsen, 1967). The envelope appears to be composed of an inner membrane having the appearance and the dimensions of a 'unit membrane', and an outer %layered structure, 75-15oA in thickness, which was shown by Stoeckenius & Rowen (1967) to be 326 H. STEENSLAND A N D H. LARSEN proteinaceous in nature.…”

Section: Introductionmentioning

confidence: 88%

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A Study of the Cell Envelope of the Halobacteria

Steensland

Larsen

1969

Journal of General Microbiology

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SUMMARYElectron microscopy on thin sections of three different extremely halophilic Halobacterium species showed that their cell envelopes were of similar general construction: an inner membrane and an outer layer. The outer layer stains most strongly in the outermost part. When the NaCl concentration of the environment was lowered from the optimal of 4-3 M to 2-2 M the outer layer of the cell envelope of Halobacterium salinarium strain I became frayed; in many cells a release of material from the outer layer appeared to take place. When the cells were exposed to distilled water the outer layer of the envelope appeared to dissolve completely and the cell membrane disintegrated into tiny flakes. Fragments of the cell envelope produced by mechanical disintegration of the cells in 4'3 M-NaCI formed closed vesicles very rapidly; some of the cytoplasmic material became trapped inside the vesicles. Detergents appeared to slow down the closing of the vesicles and also to cause a release of material from the outer layer of the cell envelope. The cell envelope vesicles were mainly composed of protein and lipid ; their content of amino sugar was low compared with the cell envelope of other Gram-negative bacteria. The cell envelope vesicle also contained nucleic acids; most of these were probably parts of the cytoplasmic material trapped inside the vesicles. The amino acid composition showed that the protein of the cell envelope vesicles was quite acidic, consistent with the contention that high concentrations of sodium ions stabilize the cell envelopes of these organisms by neutralizing the negative charges of the protein. Upon centrifugation at high speed of the lysate obtained by dialysis of the cell envelope vesicles against distilled water, the fragments of the cell membrane sedimented whereas most of the protein, presumably from the outer layer of the cell envelope, stayed in the supernatant fraction. Carotenoids and cytochromes were contained in the sediment with the membrane fragments. Most of the amino sugar-containing components stayed in the supernatant fraction; in the presence of 10-25 mM salt most of the amino sugar-containing components sediment with the membrane fragments.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 88%

A Study of the Cell Envelope of the Halobacteria

Steensland

Larsen

1969

Journal of General Microbiology

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“…Surface location of the glycoprotein Halobacteria require high salt concentrations not only for optimum growth, but for maintenance of structural integrity (3). As the salt concentration of the suspending medium is lowered the cells undergo morphological changes, and at less than 1-1.5 M NaCI, lysis occurs.…”

Section: Resultsmentioning

confidence: 99%

“…This glycoprotein accounts for all of the nonlipid carbohydrate of the cell envelope and 40-50% of the envelope protein (2). Despite the absence of a peptidoglycan layer, these bacteria are able to maintain a rod-shaped morphology under normal growth conditions (3). The large amount of glycoprotein in the cell envelope and the effect of the antibiotic bacitracin on the growth and morphology of the cells (4) suggested that the glycoprotein might play a structural role in the envelope.…”

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confidence: 99%

Structural (shape-maintaining) role of the cell surface glycoprotein of Halobacterium salinarium.

Mescher¹,

Strominger²

1976

Proc. Natl. Acad. Sci. U.S.A.

135

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“…These results indicate that the enzymes are dependent on divalent metal ions for stability and/or activity but the ions are rather firmly bound to the enzyme proteins. All enzymes of the halophilic bacteria appear to be rapidly and irreversibly denatured in ordinary buffers which do not contain large concentrations of NaCl or Enzymes jrom halophilic bacteria 255 KCl, (Larsen, 1967). The proteolytic enzymes are no exceptions to this rule and we have not been able to reactivate them by dialysis against solutions containing the salts of medium 73.…”

Section: Resultsmentioning

confidence: 89%

Proteolytic Enzymes from Extremely Halophilic Bacteria

Norberg

Hofsten

1969

Journal of General Microbiology

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S U M M A R YHalobacterium strains produce a truly extracellular proteinase which degrades gelatine and casein. It has a pH optimum of about 8 and depends upon divalent cations and a high concentration of NaCl or KC1 for activity and stability. Proteolytic enzymes were also found in cell homogenates obtained by ultra sonic treatment. A caseinolytic enzyme, probably different from the extracellular one, is associated with particles which sediment upon ultracentrifugation. A soluble peptidase of lower molecular weight is also present in the extract. Both enzymes are dependent upon divalent cations and a high concentration of NaCl or KCI for activity. In contrast to other halophilic enzymes, the proteolytic enzymes of Halobacterium sdharium are more active in the presence of NaCl than KCl at equimolar concentrations. I N T R O D U C T I O NBacteria of the genus Halobacterium are widely distributed in brines of high salt concentration. They are thus conspicuous in solar evaporation ponds of salt works, where they often become the dominating type of organisms when the salt concentration rises above 25 %. The extremely halophilic bacteria are best cultivated in complex media containing peptones and yeast extract to which at least 15 % (wlv) NaCl has been added. Best growth is obtained in media containing about 25 % salt, and when bacteria are transferred to solutions with a salt concentration of less than about 10 % they lyse rapidly.The unusual properties of halophilic bacteria make them interesting objects of study for both microbiologists and biochemists, and Larsen (1967) summarized the result of a large number of investigations on them. Special methods are often necessary in studies of their metabolism and conventional procedures are unsuitable for the purification and assay of ' halophilic ' enzymes.The extreme halophiles do not generally grow well on carbohydrates but they have a well-developed enzyme apparatus for metabolizing amino acids. In order to utilize the proteins of dead organisms in salt brines the bacteria must form proteolytic enzymes. Gibbons (1957) found that 45 out of 49 tested strains were gelatinolytic, and most of these strains also degraded casein. However, a closer study of the properties of the proteolytic enzymes of such strains has apparently not been made. It is known that the bacteria have an intracellular concentration of NaCl + KCI, which is approximately the same as the NaCl concentration of the growth medium. The halophilic bacteria's enzymes are thus active at salt concentrations which inhibit or even denature many enzymes of non-halophilic organisms. This must be reflected in marked differences in the composition and properties of the protein molecules. Ingram (1947) has

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Biochemical Aspects of Extreme Halophilism

Cited by 236 publications

References 61 publications

A Study of the Cell Envelope of the Halobacteria

A Study of the Cell Envelope of the Halobacteria

Structural (shape-maintaining) role of the cell surface glycoprotein of Halobacterium salinarium.

Proteolytic Enzymes from Extremely Halophilic Bacteria

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