Stability and comparative transport capacity of cells, mureinoplasts, and true protoplasts of a gram-negative bacterium

Separation and localization of cell wall layers of a gram-negative bacterium

The cell envelope of a marine pseudomonad as seen in thin section by electron microscopy has the double-membrane structure typical of other gram-negative bacteria. Cells washed with a solution containing Na(+), K(+), and Mg(++) at their concentrations in the growth medium, when suspended briefly in 0.5 m sucrose, lost 13% of their hexosamine in a form nonsedimentable by centrifugation at 73,000 x g. Since the resulting cells in thin section appeared unchanged, it was concluded that the material released was derived from a nonstaining, loosely bound outer layer. This same layer could be removed from the cells by washing with 0.5 m NaCl. A second nonsedimentable fraction was released after successive suspension of the cells in 0.5 m sucrose. Since this material was released only when the outer double-track structure had broken, it was concluded that it arose from a layer immediately underlying the latter layer. The three layers differed in their content of hexosamine and protein. None of the layers released contained muramic or diaminopimelic acid. The cell form remaining was rod shaped and appeared in thin section to be bounded only by its cytoplasmic membrane. This form contained all the muramic and diaminopimelic acid in the cell. Treatment with lysozyme released the muramic and diaminopimelic acid and converted the rod form to a protoplast, indicating that in the rod form (mureinoplast) a thin layer of peptidoglycan is located on the outside surface of the cytoplasmic membrane. Thus, five separate layers have been detected in the cell envelope of this marine pseudomonad.

Role of transmembrane electrical potential on cadmium fixation by a marine pseudomonad

The role of cellular energy, and mainly that of electrical transmembrane potential, in cadmium fixation by a marine pseudomonad suspended in a mineral medium was investigated by studying the effects of ionophores. Although fixation of cadmium by cells was generally less when respiratory activity was inhibited, it was not affected by a reduction of the transmembrane electrical potential delta psi in mureinoplasts. These observations strongly suggest that cadmium fixation in this isolate was not the result of a delta psi-dependent active transport.

Effects of nonionic, ionic, and dipolar ionic detergents and EDTA on the Brucella cell envelope

Cell envelopes prepared from smooth and rough strains of Brucella were characterized on the basis of lipopolysaccharide and protein content. The action of three kinds of detergents on Brucella cell envelopes and Escherichia coli control cell envelopes was examined on the basis of the proteins and lipopolysaccharides that were extracted. As compared with those of E. coli, Brucella cell envelopes were resistant to nonionic detergents. Zwittergents 312 and 316 were most effective in extracting E. coli cell envelopes, and Zwittergent 316 was most effective in extracting Brucella cell envelopes. Sarkosyl extracted proteins but extracted only trace amounts of lipopolysaccharides from cell envelopes of both bacteria. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the Sarkosyl-resistant proteins revealed a composition similar to that of the proteins exposed on the surfaces of viable cells, as determined by the lactoperoxidase-125I radioiodination method. EDTA, with either Tris-HCl or Tris-HCl-Triton X-100, did not have detectable effects on Brucella cell envelopes. Ultracentrifugation of purified lipopolysaccharides in detergents and EDTA demonstrate that, in contrast to that of E. coli, Brucella lipopolysaccharide was not stabilized by divalent cations. Sarkosyl was ineffective in dispersing lipopolysaccharides, whereas the action of Zwittergents was related to the length of their alkyl chains.

Na, k, and nonspecific solute requirements for induction and function of galactose active transport in an antarctic psychrophilic marine bacterium

An Antarctic psychrophilic marine Vibrio sp., with the inducible ability to accumulate non-metabolizable [C]methyl-beta-d-thiogalactoside through a galactose transport system, was isolated. Induction of [C]methyl-beta-d-thiogalactoside uptake was found to have a specific Na requirement which was higher than that required for maximal uptake and growth. A specific K requirement was found to be quantitatively the same for uptake, growth, and induction. At low suboptimal growth salinities in artificial seawater, growth, uptake, and induction were inhibited more by the generally low solute concentration than by a specific ion deficiency. Evidence was given that the effect of the nonspecific solute was not completely osmotic in nature. The nonspecific solute requirement was greatest for induction, followed by growth and substrate uptake.

Third system for neutral amino acid transport in a marine pseudomonad

Uptake of leucine by the marine pseudomonad B-16 is an energy-dependent, concentrative process. Respiratory inhibitors, uncouplers, and sulfhydryl reagents block transport. The uptake of leucine is Na+ dependent, although the relationship between the rate of leucine uptake and Na+ concentration depends, to some extent, on the ionic strength of the suspending assay medium and the manner in which cells are washed prior to assay. Leucine transport can be separated into at least two systems: a low-affinity system with an apparent Km of 1.3 X 10(-5) M, and a high-affinity system with an apparent Km of 1.9 X 10(-7) M. The high-affinity system shows a specificity unusual for bacterial systems in that both aromatic and aliphatic amino acids inhibit leucine transport, provided that they have hydrophobic side chains of a length greater than that of two carbon atoms. The system exhibits strict stereospecificity for the L form. Phenylalanine inhibition was investigated in more detail. The Ki for inhibition of leucine transport by phenylalanine is about 1.4 X 10(-7) M. Phenylalanine itself is transported by an energy-dependent process whose specificity is the same as the high-affinity leucine transport system, as is expected if both amino acids share the same transport system. Studies with protoplasts indicate that a periplasmic binding protein is not an essential part of this transport system. Fein and MacLeod (J. Bacteriol. 124:1177-1190, 1975) reported two neutral amino acid transport systems in strain B-16: the DAG system, serving glycine, D-alanine, D-serine, and alpha-aminoisobutyric acid; and the LIV system, serving L-leucine, L-isoleucine, L-valine, and L-alanine. The high-affinity system reported here is a third neutral amino acid transport system in this marine pseudomonad. We propose the name "LIV-II" system.

Egestion of degraded meningococci by polymorphonuclear leukocytes

Quantitative studies were carried out on the in vitro phagocytosis of 14C-labeled Neisseria meningitidis by mouse polymorphonuclear leukocytes. Intact, "loaded" leukocytes were found to excrete radioactive bacterial products back into supernatant fluids. Morphological events associated with the exocytosis events revealed a fusion between the phagocytic vacuole and plasma membranes of the leukocyte followed by an emptying of the vacuole contents. Egested materials were free from whole meningococci and consisted mainly of membranous vesicles.

Interaction of Mg-2+ with peptidoglycan and its relation to the prevention of lysis of a marine pseudomonad

Intact cells of marine pseudomonad B-16 (ATCC 19855) which have been washed with a solution of NaCl require only 0.001 M MgSO4 and 100 to 300 times this concentration of NaCl or KCl to prevent lysis. Conversion of intact cells to mureinoplasts, a process involving removal of the outer double-track layer (outer membrane) and the periplasmic space layer of the cell wall, approximately doubled the requirement for the three salts to prevent lysis. The formation of protoplasts from mureinoplasts by removing the peptidoglycan layer again doubled the requirement for Na+ and K+ salts but increased the requirement for the Mg-2+ salt 200- to 300-fold. Cells of the marine pseudomonad suspended in solutions containing Mg-2+ salts failed to lyse on subsequent repeated suspension in distilled water, whereas cells presuspended in NaCl lysed immediately. Isolated envelope layers including the peptidoglycan layer, when dialyzed against solutiions containing Mg-2+ salts, retained Mg-2+ after subsequent suspension in distilled water. Envelope layers exposed to solutions of Na+ or K+ salts failed to retain these ions after exposure to distilled water. Na+ displaced Mg-2+ from the cell envelope layers. The results obtained indicate that the capacity of Mg-2+ salts at very low concentration to prevent lysis of intact cells and mureinoplasts of this organism is due primarily to the interaction of Mg-2+ with the peptidoglycan layer of the cell wall. Ion interaction with the layers lying outside of the peptidoglycan layer contributes only a small amount to the mechanical strength of the wall.

Kinetics of Na+-dependent K+ ion transport in a marine pseudomonad

The effect of external Na plus concentration on the transport of K plus was studied using K plus-depleted cells of a marine pseudomonad. K plus transport was found to be a saturable process and requires Na plus. The initial rates for K plus transport over a range of external K plus concentrations were measured in suspensions containing various fixed concentrations of Na plus. Reciprocals of the initial rates for K plus transport were plotted against reciprocals of the external concentration of K plus or Na plus to yield two primary Lineweaver-Burk plots. The experimental data were found to fit bisubstrate enzyme kinetics, with a sequential type mechanism. However, the initial rate data did not allow distinction between ordered or random mechanisms. The results suggest that Na plus and K plus form a ternary complex with a specific K plus carrier molecule on the outer surface of the membrane prior to translocation and the release of K plus inside the cell.

Heterogeneity in lipid composition of the outer membrane and cytoplasmic membrane and cytoplasmic membrane of Pseudomonas BAL-31

The outer membranes and cytoplasmic membranes of the marine bacterium Pseudomonas BAL-31 were separated by washing the cells three times in 0.5 M NaCl and twice in 0.5 M sucrose. Electron microscopy during the removal of membranes revealed that the outer membranes fragmented in a regular manner to give rise to fairly uniform vesicles measuring approximately 140 nm in diameter. Isolated outer membranes had a buoyant density in sucrose of 1.230 g per cm(3), whereas the cytoplasmic membranes had a density of 1.194 g per cm(3). The removal of the outer membrane during the application of this procedure was monitored by measuring the release of 2-keto-3-deoxyoctulosonic acid and phospholipid. The cells lost 85.5% of their 2-keto-3-deoxyoctulosonic acid and 47.3% of their phospholipid during this treatment. Complete recovery of outer membrane material could be achieved. The removal of 25.5% of the 2-keto-3-deoxyoctulosonic acid and 0.9% of the phospholipid rendered the cells sensitive to lysis with Triton X-100. The phospholipid composition of the outer membrane was calculated to be 78.9% phosphatidylethanolamine and 16.1% phosphatidylglycerol. The phospholipid composition of the cytoplasmic membrane proved to be 71.5% phosphatidylethanolamine and 23.5% phosphatidylglycerol. The fatty acid composition was also found to be quantitatively heterogeneous between the two membranes.

Structure and function of the cell envelope of gram-negative bacteria

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Relationship of a wall-associated enzyme with specific layers of the cell wall of a gram-negative bacterium

In untreated cells of the marine pseudomonad studied here, alkaline phosphatase was found to be located in the periplasmic space, at the cell surface, and in the medium into which it had been shed during growth. Washing in 0.5 M NaCl, which removed the loosely bound outer layer, caused a shift of periplasmic enzyme to the outer aspect of the double-track layer and released some of the cell surface-associated enzyme. When the double-track layer of the cell wall was partially deranged, large amounts of this cell wall-associated enzyme were released, and, when the double-track was removed from the cells to produce mureinoplasts, alkaline phosphatase was released into the menstruum. There was no significant association of the enzyme with the peptidoglycan layer of the cell wall, which is the outermost structure of the mureinoplast, and no association of the enzyme with the cytoplasmic membrane of these modified cells. This study has shown that alkaline phosphatase is specifically associated with the outer layers of the cell walls of cells of this organism and is retained within the cell wall by virtue of this association.

Freeze-etching and x-ray diffraction of the isolated double-track layer from the cell wall of a gram-negative marine pseudomonad

The isolated double-track layer of the cell wall of the gram-negative marine pseudomonad studied here contains a cleavage plane. This finding localizes the single cleavage plane of the cell wall and shows that the molecular architecture of this layer provides the lipid-enriched layer which cleaves preferentially in the frozen cell. The observation that the isolated double-track layer of the cell wall is sufficiently ordered at the molecular level to yield a well-defined X-ray diffraction pattern with a d-spacing of 0.44 nm shows that its molecular architecture is very similar to that of true membranes. This specific d-spacing is produced by the highly ordered packing of the hydrophobic portions of phospholipid molecules. Therefore, the double-track layer of the cell wall has been shown, by these two biophysical means, to have a molecular architecture which would allow it to function as the membrane-like "molecular sieve" layer, whose presence has been deduced from physiological data. This layer is important in the retention of cell wall-associated enzymes and in the control of the movement of large molecules through the cell wall.

Effect of the removal of outer cell wall layers on the actinomycin susceptibility of a gram-negative bacterium

Removal of the outer cell wall layers of a gram-negative marine pseudomonad (B-16) showed that these cells are penetrable by actinomycin D and that, therefore, neither the cytoplasmic membrane nor the peptidoglycan layer constitutes the barrier which excludes this antibiotic from intact cells, but that this barrier is formed by the outer layers of the cell wall which include the lipopolysaccharide component and the double-track layer.

Isolation, characterization, and ultrastructure of the peptidoglycan layer of a marine pseudomonad

The peptidoglycan layer of a marine pseudomonad was observed by electron microscopy in thin sections of plasmolyzed intact cells and mureinoplasts but not in untreated intact cells. Only fragments of this layer could be isolated by sodium lauryl sulfate (SLS) treatment of mureinoplast envelopes. Sacculus-like peptidoglycan structures were obtained from growing cells by immediate heat inactivation of cellular autolytic enzymes and subsequent SLS, trypsin, and nuclease treatments. Recently, similar peptidoglycan sacculus-like structures have been obtained by adding SLS to the growing culture and treating the isolated particulate material with nucleases. Thin-sectioned and negatively stained preparations of whole cell peptidoglycan showed compressed profiles of cell-shaped sacculi. Peptidoglycan prepared by SLS treatment of mureinoplast envelopes had a similar composition to that prepared from whole cells. The major amino sugars and amino acids in the peptidoglycan component were glucosamine, muramic acid, alanine, glutamic acid and diaminopimelic acid in the molar ratios 1.18:1.24:1.77:1.00:0.79. Forty-five per cent of the epsilon-amino groups of diaminopimelic acid were cross-linked. The peptidoglycan was estimated to account for about 1% of the cell dry weight.

Structural changes during lysis of a psychorophilic marine bacterium

The marine psychrophile, a red, gram-negative motile rod with a single polar flagellum, is stable when suspended in 0.1 m Mg(2+) plus 0.5 m NaCl at 0 C and neutral pH but lyses if the salt composition of the medium is changed, the temperature raised above 20 C, or the pH lowered. Lysis is accompanied by a fall in turbidity, a release of ultraviolet-absorbing substances, and a loss of deoxyribonucleic acid and ribonucleic acid. Ultrastructural changes accompanying lysis were studied. Thin sections of cells fixed while intact showed a triple-layered cell wall and cytoplasmic membrane, each 6.0 to 7.5 nm thick. Mesosomes were also observed. Either Na(+) or Mg(2+) could maintain wall integrity, whereas Mg(2+) was needed for membrane integrity. In distilled water, lysis was very extensive, and much material was released as wall fragments and as vesicles which probably came from the wall and cytoplasmic membrane. Lysis at 37 C resulted in degradation of the wall and liberation of wall fragments. The cell membrane was rarely observed as a triple-layered structure in such temperature-lysed cells. After lysis at pH 5.0, the cell wall was distorted, and only a suggestion of the cell membrane remained. Replicas showed that this organism had a matted surface which was distorted under different conditions of lysis.

Demonstration by freeze-etching of a single cleavage plane in the cell wall of a gram-negative bacterium

In the examination of protoplasts of a gram-negative bacterium classified as a Pseudomonas sp. by freeze-etching, we found a smooth external surface which is not seen if the preparations are not "etched." This external structure is seen as a sleeve surrounding and connecting the cells in unetched preparations, and we present evidence that it is a eutectic formed during the freezing of the specimen. In the system used in this study, the four layers of the cell wall of a gram-negative bacterium can be removed from the cell. The single cell wall cleavage plane is not affected by the removal of the loosely bound outer layer or of the peptidoglycan layer, but it is lost when the outer double track layer and the underlying soluble layer are simultaneously removed. Thus, we conclude that it is one of these two layers which is responsible for the cleavage plane which exposes variable areas of a smooth surface in the cell wall. This cell wall cleavage plane is more likely to deflect the actual cleavage of the frozen cell when cells are relatively old or when they are suspended in sucrose.

Isolation and chemical composition of the cytoplasmic membrane of a gram-negative bacterium

With procedures developed previously in this laboratory, the various layers of the cell wall of a gram-negative bacterium, a marine pseudomonad (ATCC 19855), were removed completely giving rise to true protoplasts. Membranes were isolated from the protoplasts formed. After treatment with ribonuclease, deoxyribonuclease, and washing, the membranes isolated were shown by electron microscopy and chemical analysis to be essentially free from both wall material and cytoplasmic constituents. The membranes gave rise to a single compact band in a sucrose density gradient. All of the lipid and protein were found to be associated in the membrane band. Analysis showed the membranes to contain 30.5% lipid (78% of which was phospholipid), 62.8% protein, and 2% carbohydrate. The predominant phospholipid present was phosphatidylethanolamine with a lesser amount of diphosphatidylglycerol and traces of unidentified compounds.

K plus-dependent deplasmolysis of a marine pseudomonad plasmolyzed in a hypotonic solution

When cells of a marine pseudomonad were washed with a solution consisting of 0.3 m NaCl, 0.05 m MgSO(4), and 0.01 m KCl (complete salts), they maintained their normal morphology. When washed with a solution of 0.05 m MgSO(4), they became plasmolyzed as indicated by both phase and electron microscopy. Suspensions of cells washed with 0.05 m MgSO(4) showed an increase in optical density (OD) when 0.3 m NaCl was added, and this was followed by a decrease in OD upon the further addition of 0.01 m KCl. Salts of other monovalent cations were not effective in replacing K(+) in producing the OD decrease. Phase-contrast microscopy revealed that the increase in OD was accompanied by a decrease in cell size, and the decrease in OD, by an increase in the cell size. Both phase and electron microscopy showed that the K(+)-dependent decrease in OD was accompanied by deplasmolysis of the cells. Na(+) was required in the suspending medium in addition to K(+) to obtain deplasmolysis. The intracellular K(+) concentration in cells which had been washed with complete salts and which had retained their normal morphology was found to be 0.290 m. In cells plasmolyzed by washing with 0.05 m MgSO(4), the intracellular K(+) concentration was 0.004 m. Deplasmolyzed cells contained 0.330 m K(+). The membrane profile of plasmolyzed cells was retained when protoplasts were formed. The protoplasts became spherical if incubated in a solution permitting the deplasmolysis of the parent cells. The evidence obtained indicates that plasmolysis and deplasmolysis under the conditions described was due to the loss and gain, respectively, of K(+) by the cells. The effect of Na(+) could be ascribed to its capacity to control the porosity of the cytoplasmic membrane of this organism.