Turnover of the Cell Wall of Gram-positive Bacteria

Cell wall turnover in phosphate and potassium limited chemostat cultures of Bacillus subtilis W23

Turnover in phosphate and potassium limited chemostat cultures of Bacillus subtilis W23 results in the release of over 80% of the wall material present at the time of chasing equilibrium-labelled cultures. The rate at which turnover proceeds is faster in potassium limited cultures than in phosphate limited cultures but in both cases a fraction of the wall material appears to be conserved, or to undergo turnover at a lower rate. Previously we have shown that the polar wall is less active metabolically than the cylindrical wall and it is possible that the apparently conserved wall is that present in the pole.

Cell wall turnover in growing and nongrowing cultures of Bacillus subtilis

Cell wall turnover was studied in cultures of Bacillus subtilis in which growth was inhibited by nutrient starvation or by the addition of antibiotics. Concomitantly, the synthesis of wall, as measured by the incorporation of radioactively labeled N-acetylglucosamine, was followed in some of these cultures. In potassium- or phosphate-starved cultures, growth stopped, but wall turnover continued at a rate slightly lower than that in the control cultures. Lysis of cells did not occur. In glucose-starved cultures, continued wall turnover caused lysis of cells, since wall synthesis apparently was inhibited. The same phenomenon was observed after growth arrest by the addition of wall synthesis inhibitors such as fosfomycin, cycloserine, penicillin G, and vancomycin. Growth arrest by the addition of chloramphenicol allowed the continuation of wall synthesis; therefore, the observed turnover generally did not cause cell lysis.

Cell wall metabolism in Bacillus subtilis subsp. niger: accumulation of wall polymers in the supernatant of chemostat cultures

Cell wall polymers were measured both in the cells and in the cell-free medium of samples from steady-state chemostat cultures of Bacillus subtilis, growing at various rates under magnesium or phosphate limitation. The presence of both peptidoglycan and anionic wall polymers in the culture supernatant showed the occurrence of wall turnover in these cultures. Variable proportions of the total peptidoglycan present in the culture samples were found outside the cells in duplicate cultures, indicating that the rate of peptidoglycan turnover is variable in B. subtilis. Besides peptidoglycan, anionic wall polymers were detected in the culture supernatant: teichoic acid in magnesium-limited cultures and teichuronic acid in phosphate-limited cultures. In several samples, the ratio between the peptidoglycan and the anionic polymer concentrations was significantly lower in the extracellular fluid than in the walls. This divergency was attributed to the occurrence of direct secretion of anionic polymers after their synthesis.

Cell wall turnover in batch and chemostat cultures of Bacillus subtilis

Wall turnover was studied in Bacillus subtilis. The loss of radioactively labeled wall polymers was followed during exponential growth in batch and chemostat cultures. Turnover kinetics were identical under all growth conditions; pulse-labeled wall material was lost with first-order kinetics, but only after exponential growth for 1 generation time after its incorporation. Similarly, continuously labeled cells showed an accelerating decrease in wall-bound radioactivity starting immediately after removal of the labeled precursor and also reached first-order kinetics after 1 generation time. A mathematical description was derived for these turnover kinetics, which embraced the concept of "spreading" of old wall chains (H. M. Pooley, J. Bacteriol. 125:1127-1138, 1976). Using this description, we were able to calculate from our experimental data the rate of loss of wall polymers from cells and the fraction of the wall which was sensitive to turnover. We found that about 20% of the wall was lost per generation time and that this loss was affected by turnover activity located in the outer 20 to 45% of the wall; rather large variations were found with both quantities and also between duplicate cultures. These parameters were quite independent of the growth rate (the specific growth rate varied from 1.3 h-1 in broth cultures to 0.2 to 0.3 h-1 in chemostat cultures) and of the nature of the anionic polymer in the wall (which was teichoic acid in cultures with an excess of phosphate and teichuronic acid in phosphate-limited chemostat cultures). Some implications of the observed wall turnover kinetics for models of wall growth in B. subtilis are discussed.

Extracellular proteases modify cell wall turnover in Bacillus subtilis

The rate of turnover of peptidoglycan in exponentially growing cultures of Bacillus subtilis was observed to be sensitive to extracellular protease. In protease-deficient mutants the rates of cell wall turnover were greater than that of wild-type strain 168, whereas hyperprotease-producing strains exhibited decreased rates of peptidoglycan turnover. The rate of peptidogylcan turnover in a protease-deficient strain was decreased when the mutant was grown in the presence of a hyperprotease-producing strain. The addition of phenylmethylsulfonyl fluoride, a serine protease inhibitor, to cultures of hyperprotease-producing strains increased their rates of cell wall turnover. Isolated cell walls of all protease mutants contained autolysin levels equal to or greater than that of wild-type strain 168. The presence of filaments, or cells with incomplete septa, was observed in hyperprotease-producing strains or when a protease-deficient strain was grown in the presence of subtilisin. The results suggest that the turnover of cell walls in B. subtilis may be regulated by extracellular proteases.

Morphological and physiological study of autolytic-defective Streptococcus faecium strains

Three autolytic-defective mutants of Streptococcus faecium (S. faecalis ATCC 9790) were isolated. All three autolytic-defective mutants exhibited the following properties relative to the parental strain: (i) slower growth rates, especially in chemically defined medium; (ii) decreased rates of cellular autolysis and increased survival after exposure to antibiotics which block cell wall biosynthesis; (iii) decreased rates of cellular autolysis when treated with detergents, suspended in autolysis buffers, or grown in medium lacking essential cell wall precursors; (iv) a reduction in the total level of cellular autolytic enzyme (active plus latent forms of the enzyme); (v) an increased ratio of latent to active forms of autolysin; and (vi) increased levels of both cellular lipoteichoic acid and lipids.

Cell wall teichoic acid as a reserve phosphate source in Bacillus subtilis

Although exponential growth of Bacillus subtilis 168 in a phosphate-limited medium halted with the exhaustion of inorganic phosphate, the bacteria continued to grow at a slower rate for a further 3 to 4 h at 37 degrees C. This postexponential growth in the absence of an exogenous phosphate supply was accompanied by a loss of teichoic acid from the cell walls of the bacteria. Quantitative analysis of walls and culture fluids showed that the phosphate loss from the walls could not be accounted for by an increase in phosphate-containing compounds in the medium, which implied that the cells were using their own wall teichoic acids to supply phosphate necessary for growth. Addition of exogenous teichoic acid to phosphate-starved cultures resulted in stimulation of growth and in the simultaneous disappearance of teichoic acid phosphate from the medium. It is proposed that teichoic acids, which can contain more than 30% of the total phosphorus of exponential-phase cells, can be used as a reserve phosphate source when the bacteria are starved for inorganic phosphate.

Autolysins and shape change in rodA mutants of Bacillus subtilis

The biochemical phenotype of rodA mutants was not affected by the simultaneous presence in double mutants of the lyt gene which makes them 90 to 95% deficient in autolysin action. The only morphological effect of this deficiency on the expression of the rod gene was that both the rod and the coccal forms of the mutant failed to separate and grew as long chains of cells. Inhibition of protein synthesis stopped the increase in peptidoglycan that occurred when the growth temperature for the mutants was raised to 45 degrees C. These observations support the idea that a derepression of peptidoglycan synthesis occurs at this temperature. The increased amount of cellular peptidoglycan at the higher growth temperature is not likely to be the result of the concomitant switching off of autolytic enzyme action.

Autolytic defective mutant of Streptococcus faecalis

Properties of a variant of Streptococcus faecalis ATCC 9790 with defective cellular autolysis are described. The mutant strain was selected as a survivor from a mutagenized cell population simultaneously challenged with two antibiotics which inhibit cell wall biosynthesis, penicillin G and cycloserine. Compared to the parental strain, the mutant strain exhibited: (i) a thermosensitive pattern of cellular autolysis; (ii) an autolytic enzyme activity that had only a slightly increased thermolability when tested in solution in the absence of wall substrate; and (iii) an isolated autolysin that had hydrolytic activity on isolated S. faecalis wall substrate indistinguishable from that of the parental strain, but that was inactive when tested on walls of Micrococcus lysodeikticus as a substrate. These data indicate an alteration in the substrate specificity of the autolytic enzyme of the mutant which appears to result from the synthesis of an altered form of autolytic enzyme.

[Maintenance metabolism in glucose-limited chemostat cultures of Streptomyces hygroscopicus]

Investigations with the mycelium forming bacterium Streptomyces hygroscopicus IMET JA 6599 in glucose-limited chemostat cultures gave a maintenance coefficient of m = 0.031 h-1. This low maintenance coefficient corresponds to those of moulds (RIGHELATO et al. 1968, CARTER et al. 1971). With a simple model structured in active and inactive biomass (x1 and x2) it was tried to explain the low maintenance coefficient of S. hygroscopicus in relation to nonfilamentous growing microorganisms. The model contains the transition rate k, which describes the transition of active biomass in inactive one and the decay rate beta, which considers the decay of hyphae. The model was used to study the influence of beta on the maintenance coefficient and it was shown that maintenance metabolism can be simulated by the parameter beta alone.

Relation between cell wall turnover and cell growth in Bacillus subtilis

The kinetics of cell wall turnover in Bacillus subtilis have been examined in detail. After pulse labeling of the peptidoglycan with N-acetylglucosamine, the newly formed peptidoglycan is stable for approximately three-quarters of a generation and is then degraded by a process that follows first-order kinetics. Deprivation of an auxotroph of amino acids required for protein synthesis results in a cessation of turnover. If a period of amino acid starvation occurs during the lag phase of turnover, then the initiation of turnover is delayed for a period of time equivalent to the starvation period. During amino acid starvation, new cell wall peptidoglycan is synthesized and added to preexisting cell wall. This peptidoglycan after resumption of growth is also subject to degradation (turnover). It is suggested that cell wall turnover is dependent on cell growth and elongation. Several possible control mechanisms for cell wall autolytic enzymes are discussed in light of these observations.

Synthesis of cell envelope components by anucleate cells (minicells) of Bacillus subtilis

Minicells produced by Bacillus subtilis CU403 (divIVB1) are capable of mucopeptide biosynthesis as shown by the incorporation of L-alanine, D-alanine, and N-acetylglucosamine into trichloroacetic acid-precipitable material, which can be degraded to trichloroacetic acid-soluble material by lysozyme digestion. Incorporation of the precursors is sensitive to vancomycin and D-cycloserine and insensitive to chloramphenicol. Penicillin inhibits the incorporation of D- and L-alanine N-acetylglucosamine at concentrations in excess of 10 mug of penicillin per ml; however, minicells are insensitive to penicillin-induced lysis. The material synthesized in minicells from N-acetylglucosamine is not subject to turnover during a subsequent 6-h incubation period. [2-3H]glycerol is converted to a cold trichloroacetic acid-precipitable form by minicells. This synthesis is not inhibited by vancomycin, penicillin, D-cycloserine, or chloramphenicol. Fractionation of the material synthesized from glycerol into hot trichloroacetic acid-soluble material and chloroform/methanol-extractable material indicates that minicells convert glycerol into teichoic acid and lipid.

Membrane lipoteichoic acid of Streptococcus pyogenes and its stabilized L-form and the effect of two antibiotics upon its cellular content

Membrane lipoteichoic acid continues to be synthesized by an osmotically fragile, stabilized L-form of Streptococcus pyogenes. Chromatographic and electrophoretic comparisons indicate that the lipid componenent of lipoteichoic acid in this L-form and its parental streptococcus is glycerophosphoryldiglucosyl diglyceride and not phosphatidylkojibiosyl diglyceride. Based upon dry weight determinations, the yield of lipoteichoic acid from the L-form is 0.19%, as compared with 0.97% from the streptococcus. When grown with bacitracin the L-form contains the same amount of teichoic acid as when grown without this antibiotic; however, its lipoteichoic acid content is reduced by 85%. Similarly, the L-form grown with novobiocin for 10 h contains only 17% of the teichoic acid found in control cells.

Cell wall assembly in Bacillus subtilis: development of bacteriophage-binding properties as a result of the pulsed incorporation of teichoic acid

Addition of a pulse of excess phosphate to a phosphate-limited culture of Bacillus subtilis W23 resulted in the synthesis and incorporation of wall material that contained teichoic acid. Consequently, the bacteria regained the ability to bind phage SP50 although maximum phage-binding properties did not develop until approximately half a generation time after incorporation of teichoic acid had ceased. The present findings strongly support our earlier suggestion that newly synthesized receptor material is incorporated at the inner surface of the wall and becomes exposed at the outer surface only during subsequent growth.

Characterization of the N-acetylmuramic acid L-alanine amidase from Bacillus subtilis

The N-acetylmuramic acid L-alanine amidase from Bacillus subtilis W-23 has been purified to apparent homogeneity. The enzyme is a monomer of molecular weight 51,000, which binds extremely tightly to homologous cell walls but not to heterologous cell walls, even of the closely related strain B. subtilis ATCC 6051. This difference in binding is only in part due to differences in teichoic acid between these two strains and to a large extent appears to represent differences in the arrangement of the peptidoglycan. A comparison of the amidase from B. subtilis W-23 and the enzyme previously purified from B. subtilis ATCC 6051 (Herbold and Glaser, 1975) shows that the two proteins, which cleave the same bond and are of the same size, do not cross-react immunologically and that the two enzymes are, therefore, not closely related in structure.

Peptidoglycan synthesis and turnover in cell division mutants of Agmenellum

The synthesis and turnover of peptidoglycan in Agmenellum quadruplicatum was investigated using D-[U-14C]alanine followed by proteolytic digestion. The rate of turnover of alanine in the peptide portion of the peptidoglycan was measured in strain BG-1 and in two division mutants of this strain: one was blocked in cell separation; and the other was a low-temperature, conditional cell division mutant. The peptide portion of peptidoglycan turned over in all three strains tested, but no correlation was observed between septum formation or cell separation and the rate of turnover. Peptidoglycan synthesis was measured during induced division in snake forms of strain SN-29. A stimulation of peptidoglycan synthesis was observed during the period of cross-wall formation, even in the absence of new protein synthesis. Thus in A. quadruplicatum, cross-wall synthesis is accompanied by a stimulation of peptidoglycan synthesis.

Chemical composition and turnover of peptidoglycan in Neisseria gonorrhoeae

The peptidoglycan of all four colonial types of a number of strains of Neisseria gonorrhoeae constituted 1 to 2% of the dry weight of the cell. The chemical composition of cell types examined was similar with molar ratios of 1:1:2:1:1 for muramic acid, glucosamine, alanine, glutamic acid, and diaminopimelic acid, respectively. Ninety-six percent of the mass of the peptidoglycan was composed of these compounds. A lipoprotein analogous to that observed in Escherichia coli was not detected. The chain length of the glycan varied from 80 to 110 disaccharide units. The peptide contained equimolar amounts of D- and L-alanine. The rate of turnover of peptidoglycan in strain RD5 was 50% per generation. Turnover proceeded without a lag and followed first-order kinetics.

Layered distribution, according to age, within the cell wall of bacillus subtilis

When soluble autolytic activity was added to growing cultures of a mutant possessing a reduced rate of cell wall turnover, there was a delay of more than one generation before solubilization of new cell wall began, in contrast to the immediate increase in the rate of solubilization of old cell wall. A similar delay was found before turnover of new cell wall occurred in the parent, in agreement with a previous report (Mauck et al., 1971). When sodium lauryl sulfate-inactivated cell walls were prepared, the great bulk of the wall formed a uniformly susceptible substrate to added autolytic activity. The immediate solubilization of new wall eliminates insusceptibility to autolytic enzyme as an explanation for the failure to be turned over. There were, however, major differences in the rate of solubilization of wall of different ages. During solubilization of the initial 30% of the cell wall preparation, wall two generations old was solubilized at least seven times faster than wall one-half a generation old. This result is interpreted in terms of differences in accessibility. The cell wall is seen as consisting of a series of layers, the age of which increases with the distance from the membrane, such that wall newly synthesized on the membrane passes out through the thickness of the cell wall layer during subsequent growth and only becomes susceptible to turnover as it reaches the outer surface, largely in the form of a layer, more than one generation after incorporation.

Bacteriophage SP50 as a marker for cell wall growth in Bacillus subtilis

When grown under conditions of phosphate limitation, Bacillus subtilis W23 lacked wall teichoic acid and did not adsorb phage SP50. During transition from growth under conditions of phosphate limitation to those of potassium limitation, the bacteria developed an ability to adsorb phage which increased exponentially in relation to their content of wall teichoic acid. During transition in the reverse direction, the bacteria retained near-maximum phage-binding properties until their content of wall teichoic acid had fallen to a fairly low level. These observations suggest that newly incorporated wall material does not immediately appear at the cell surface in a structure to which phage can adsorb. Examination of the location of adsorbed phage particles showed that recently incorporated receptor material appeared at the cell surface first along the length of the cylindrical portion of the cell. The results are consistent with models of wall assembly in which newly synthesized wall material is intercalated at a large number of sites that are distributed along the length of the cell. This newly incorporated material may be located initially at a level underlying the surface of the cell and may become exposed at the surface only during subsequent growth. Incorporation of new material may also proceed rapidly into the developing septa, but new wall material is incorporated into existing polar caps more slowly, or perhaps not at all.

Turnover and spreading of old wall during surface growth of Bacillus subtilis

The steady-state concentration of cell wall turnover products in the medium of Bacillus subtilis 168 growing exponentially on a casein hydrolysate-supplemented medium is equivalent to an overall rate of turnover of less than 10% per generation. After transfer of a steady-labeled culture to nonradioactive medium, the rate of release of labeled turnover products increased exponentially for up to two generations. The rate of turnover finally attained by this culture reached an apparently first-order rate of about 50% per generation. The addition of soluble autolytic activity to growing cultures of a mutant possessing a reduced rate of wall turnover resulted in a marked stimulation in the rate of solubilization of the cell wall fraction. The increased rate of solubilization produced was proportional to the concentration of added enzyme and remained constant until less than 20% of the wall originally present was left. Autolytic activity added under these conditions was bound entirely to wall at least one generation old. The results are interpreted in terms of a model for cell wall growth in which wall two or more generations old covers a total surface area at least four times larger than that occupied at the time of synthesis, forming a shallow outer layer (overlying newer wall) from which all turnover takes place. The model is discussed in relation to previous attempts to determine the pattern of surface expansion in bacilli.

Purification and properties of beta-N-acetylglucosaminidase from Escherichia coli

beta-N-acetylglucosaminidase (EC 3.2.1.30) has been purified from Escherichia coli K-12 to near homogeneity based on polyacrylamide gel electrophoresis in both 0.5% sodium dodecyl sulfate and in 6 M urea at pH 8.5. The purified enzyme shows a pH optimum of 7.7 and the Km for p-nitrophenyl-beta-D-2-acetamido-2-deoxyglucopyranoside is 0.43 mM. The molecular weight of this enzyme, determined by both Sephadex gel filtration and by sodium dodecyl sulfate gel electrophoresis, is equivalent to 36,000. It is shown to be a soluble cytoplasmic enzyme. Studies on the substrate specificites of the purified enzyme indicate that this enzyme is an exo-beta-N-acetylglucosaminidase.

Control of membrane protein synthesis in Bacillus subtilis

In synchronous cultures of Bacillus subtilis 168/S grown on succinate as a sole carbon source (mean generation time 115 min), chromosome initiation occurs at the beginning of the cell cycle but the rate of membrane protein synthesis doubles in mid-cycle more or less coincident with nuclear segregation. In glucose-grown cultures, the doubling in rate of membrane protein synthesis occurs at about the same time as nuclear segregation and DNA initiation at the beginning of the cycle. Control of the rate of membrane synthesis by the chromosome has been demonstrated by inhibiting DNA synthesis using thymine starvation and showing that membrane protein synthesis continues at a constant rate, whereas the rate of cytoplasmic protein synthesis almost doubles. I suggest that the replication of a region at or close to the chromosome terminus is required to allow the doubling in rate of membrane synthesis.

Pleiotropic phenomena in autolytic enzyme(s) content, flagellation, and simultaneous hyperproduction of extracellular alpha-amylase and protease in a Bacillus subtilis mutant

A mutant of Bacillus subtilis 6160 that had been isolated by its hyperproduction of alpha-amylase and protease lacked flagella and motility, and its content of autolytic enzyme(s) was reduced to one-third to one-fourth that of the parent. These phenotypic differences were completely co-transferred by the deoxyribonucleic acid (DNA) of the mutant when five DNA recipient strains of B. subtilis were transformed. The revertants, isolated by motility with a frequency of approximately 10(-7), recovered a normal level of autolytic activity and showed reduced productivity of alpha-amylase and protease. This point mutation allowed normal flagellin synthesis, spore formation, and rate of growth. The comparison of cell envelope of the mutant with that of the parent indicated that there was no significant difference except loss of flagella. Therefore the association at the cell surface of a group of extracellular proteins consisting of alpha-amylase, proteases, flagellin, and autolytic enzymes(s) seem to be coordinately regulated by the gene or seem to be affected coordinately by certain undetected alterations of the cell envelope.

Wall mannan of Saccharomyces cerevisiae. Metabolic stability and release into growth medium

Selective labelling of cell wall mannan with radioactive precursors in growing Saccharomyces cerevisiae showed that this polysaccharide is metabolically stable during exponential growth. Mannan once inserted into the wall is not subject to turnover or release into the growth medium. However, about 10% of the amount of mannan incorporated into the cell wall fraction can be recovered in the non-dialyzable material isolated from the growth medium. Therefore, the mannan escaping from the cell must be either a mannan de novo synthesized, not trapped in the growing wall structure, or a mannan with a non-structural role. Radioactivity was also retained in the wall fraction of cells pre-labelled with [14C] glucose which pointed to metabolic stability of all cell wall polysaccharides in growing S. cerevisiae.

Mode of cell wall synthesis in gram-positive bacilli

Ultrastructural experiments on plasmolyzed cells suggested that the information for the position and orderly synthesis of septa is not determined by the attachment of cell membrane to previously formed wall. These experiments, in conjunction with others on cells disrupted by the freeze-fracture technique, are most consistent with wall growth over the entire surface of the rods, with wall material gradually moving from a position next to the cell membrane to a position at the outer surface of the cell.

Study of cell wall growth in Bacillus megaterium by high-resolution autoradiography

Growth of the cell wall of Bacillus megaterium was studied by pulse-labeling the cell wall of a DAP- Lys- mutant for a very short time with tritium-labeled diaminopimelic acid. The distribution of radioactivity along the cell wall was examined by high-resolution autoradiography on isolated cell walls and thin sections of bacteria. The results indicate that cell wall elongation occurs by diffuse intercalation of newly synthesized murein into the expanding cell wall during exponential growth, as well as during germination, and that the only zone of highly localized diaminopimelic acid incorporation is found at the cross wall during its synthesis. This zone contains about 30% of the radioactivity incorporated into the cell wall. Analysis of autoradiographs of thin sections of bacteria shows that the total radioactivity incorporated per bacterium doubles during the life cycle. This doubling occurs in the cylindrical part of the cell wall but not in the polar caps. This seems to indicate that elongation of the bacterium is not constant during the life cycle but increases with the length of the cell.

Relationship of macromolecular synthesis to competence induction in a group H streptococcus

Group H streptococcus strain Wicky, which was induced to competence for genetic transformation with competence factor (CF) derived from a related strain, displayed reduced rates of ribonucleic acid (RNA) and peptidoglycan synthesis. Pulse-labeling studies revealed that the inhibition of both RNA and peptidoglycan synthesis was maximal at the peak of competence and decreased as competence declined. These studies indicated that competence induction had only a slight effect on the rate of protein synthesis. Trypsin inactivation of CF prevented the reductions in synthesis normally elicited by CF preparations. If the addition of trypsin was delayed until 5 min after the addition of CF, competence induction and decreased synthesis of RNA and peptidoglycan were again apparent. Thus, the alterations in the synthesis of these macromolecules appeared to be related to the induction of competence. Further studies indicated that the apparent reductions in biosynthesis were not caused by decreased uptake of the labeled precursors by intact Wicky cells. In addition, these effects were probably not the result of turnover of macromolecules induced by CF. The lack of turnover of labeled peptidoglycan suggested that competence induction may not involve an autolysin.

Regulation of bacterial cell walls: turnover of cell wall in Staphylococcus aureus

The cell wall of Staphylococcus aureus was shown to undergo turnover during exponential growth. The rate of turnover, about 15% per generation, was identical for both cell wall polymers, peptidoglycan and teichoic acid. Both the old and newly synthesized wall material appeared to undergo turnover at similar rates. The rate of turnover followed first-order kinetics until more than 90% of the original wall was lost. Cell wall turnover was completely blocked under conditions of unbalanced synthesis known to inhibit cellular autolysis, e.g., addition of chloramphenicol. Cell wall turnover was shown to occur in a number of different strains of S. aureus and appears to be widely distributed in this species.

Lipoteichoic acid localization in mesosomal vesicles of Staphylococcus aureus

Mesosomal vesicles and plasma membranes of Staphylococcus aureus ATCC 6538P have been prepared and examined for the presence of lipoteichoic acid. Lipids were first removed by treatment with pyridine-acetic acid-butanol (22:31:100, vol/vol/vol) and chloroform-methanol (2:1, vol/vol). Subsequently, lipoteichoic acid was removed with 40% phenol in water. The lipoteichoic acid from mesosomal vesicles was characterized by (i) equimolar glycerol and phosphate, (ii) alanine upon hydrolysis (2 N NH(4)OH, 18 h, 22 C), and (iii) fatty acids, diglycerol triphosphate, glycerol monophosphate, and glycerol diphosphate upon alkaline hydrolysis (1 N NaOH, 3h, 100 C). The plasma membranes contained no lipoteichoic acid. The presence in mesosomal vesicles of 18% of the dry weight as lipoteichoic acid and its absence from plasma membranes provide the first major chemical differences between these organelles. A study of the lipoteichoic acid content in various fractions of the cell showed that the mesosomal vesicles were the major and probably the sole site for the localization of the lipoteichoic acid in these organisms. A new method for the preparation of mesosomes in increased yields is reported. A theory for the control of cell division involving lipoteichoic acid and the mesosome is proposed.

Characterization of Bacillus licheniformis 6346 mutants which have altered lytic enzyme activities

Two groups of mutants altered in lytic enzyme activities have been isolated from Bacillus licheniformis 6346 MH-1 by screening clones for halo production in agar plates containing cell wall conjugated with Procion brilliant red. In the first group which produced halos during colony formation, two were shown to contain three- and eightfold more muramyl-l-alanine amidase than the parent. These strains liberated amidase and intracellular alpha-glucosidase into the culture medium during exponential growth in liquid medium. Isolated walls had a normal qualitative composition and in autolysing liberated N-terminal amino acids and reducing groups. Wall preparations from the second group of mutants which did not produce halos lysed very poorly at pH 9.5, the optimal pH for amidase activity, and poorly at pH 5.5 even though they had similar endo-N-acetylglucosaminidase activities to the parent. Two of these strains that were also deficient in phosphoglucomutase had only 3 to 5% of the membrane-bound amidase activity compared with that in the parent. Cell walls of the phosphoglucomutase-deficient mutants treated with sodium dodecyl sulfate to inactivate endogenous lytic enzymes were dissolved at 10% of the rate of those from the parent by added amidase, but their sensitivities to lysozyme were similar. Those from one mutant had 10 to 20% of the amidase-binding capacity of parent walls, whereas its isolated mucopeptide was essentially inactive in this respect. The failure of these phosphoglucomutase-deficient mutants to autolyse is likely to be due to the combined effects of both low amidase activity and resistant walls. As a result, daughter cells are unable to separate and long chains are formed during exponential growth.

Cell wall turnover at the hemispherical caps of Bacillus subtilis

Cell walls made by Bacillus subtilis bacteria grown in D(2)O medium have buoyant densities in CsCl which are different from walls made by cells grown in H(2)O medium. Cell wall turnover was studied by measuring the change in wall buoyant density after a B. subtilis culture was shifted from growth in D(2)O medium to aeration in H(2)O medium. Walls from the hemispherical caps were isolated after preferential digestion of wall from the cylindrical regions using the B. subtilis autolytic amidase. The walls from the polar regions were found to turn over extensively.

Physiological studies of Bacillus subtilis minicells

Minicells produced by Bacillus subtilis strains carrying the div IV-B1 mutation, (CU 403 div IV-B1 and CU 403 div IV-B1, tag-1), were purified by a procedure which destroys parental cells with ultrasound, but spares minicells. Such preparations generally contain 10(9) or more minicells/ml and less than 10(4) colony-forming units/ml. Purified minicells are resistant to autolysis in tris(hydroxymethyl)aminomethane buffer, pH 7.5, at 30 C, conditions which result in total lysis of parental cells. Minicells are not completely devoid of autolytic activity, however. The medium in which minicells are produced, the temperature at which purified minicells are incubated, and the genotype of cells from which the minicells are derived all influence the rate of autolysis of purified minicells. These parameters are demonstrated by using minicells obtained from div IV-B1 and div IV-B1, tag-1 strains. Ultrastructural differences have been observed in the products of autolysis of these two minicell strains. Minicells are sensitive to low levels of lysozyme and yield miniprotoplasts when the wall is removed in an osmotically protective environment. Although minicells are unable to grow, they can maintain their integrity over long periods of time, which suggests functional energy metabolism in minicells. Direct measurements of adenosine 5'-triphosphate (ATP) levels by the luciferase assay indicated that minicells can produce ATP. Oxygen consumption, measured by standard respirometry techniques, also indicates functional metabolism in minicells. These findings demonstrate that minicells purified by ultrasound are suitable material for study of physiological processes in anucleate cells.

Mutant of Bacillus subtilis lacking exo-beta-N-acetylglucosaminidase activity

A procedure for the isolation of exo-beta-N-acetylglucosaminidase mutants, by using a plate assay method incorporating a fluorescent substrate, has been developed. A mutant lacking exo-beta-N-acetylglucosaminidase activity has been isolated and shown to grow, divide, autolyze, and sporulate as well as the parental strain.