Adaptation of Bacillus megatherium to terramycin (oxytetracycline). (65/655)

B. megatherium cultures contain a few cells per hundred million which are able to grow in the presence of terramycin. Growth of the other cells is inhibited by the antibiotic with the result that the resistant cells overgrow the culture. The resistant cells are present in the culture, without contact with terramycin, and are able to grow in the presence of terramycin, without further modification. The resistant cells are mutants of sensitive cells.  (+info)

The effect of ultraviolet and white light on growth rate, lysis, and phage production of Bacillus megatherium. (66/655)

Cultures of megatherium 899a, growing under different conditions, were exposed to ultraviolet or white light. 1. Cultures exposed to ultraviolet light and then to white light continue to grow at the normal rate. Cultures exposed to ultraviolet light and then placed in the dark grow at the normal rate for varying lengths of time, depending on conditions, and then lyse with the liberation of from 5 to 1000 phage particles per cell, depending on the culture medium. 2. Increasing the time of exposure to ultraviolet light results in an increase in the fraction of cells which lyse in the dark. The lysis time decreases at first, remains constant over a wide range of exposure, and then increases. The lysis can be prevented by visible light after short exposure, but not after long exposures. 3. The time required for lysis is independent of the cell concentration. 4. Effect of temperature. After exposure to ultraviolet the cell concentration increases about 4 times at 20 degrees , 30 degrees , or 35 degrees C., but only 1.5 to 2.0 times at 40-45 degrees . This is due to the fact that the growth rate of the culture reaches a maximum at 38 degrees while the lysis rate increases steadily up to 45 degrees . 5. Terramycin decreases the growth rate and lysis rate in proportion. 6. At pH 5.1, the cultures continue to grow slowly in the dark after exposure to ultraviolet light. 7. Megatherium sensitive cells infected with T phage lyse more rapidly than ultraviolet-treated 899a, and visible light does not affect the lysis time. The results agree with the assumption that exposure to ultraviolet results in the production of a toxic (mutagenic) substance inside the bacterial cell. This substance is inactivated by white light.  (+info)

The proportion of terramycin-resistant mutants in B. megatherium cultures. (67/655)

The number of terramycin-resistant mutants in Bacillus megatherium cultures, their mutation rate, and the growth rate of the wild and mutant cells have been determined under various conditions. These values are in agreement with the following equations (Northrop and Kunitz, 1957):- See PDF for Equation lambda = mutation rate, A = growth rate constant of wild cells, B = growth rate constant of mutants, See PDF for Equation equilibrium. The value of the mutation rate as determined from equation (6) agrees with that found by the null fraction method.  (+info)

Cytological and chemical studies of the growth of protoplasts of Bacillus megaterium. (68/655)

Aeration of protoplasts of Bacillus megaterium in a succinate buffered nutrient broth led to marked growth similar to that already described by McQuillen, and the degree of chromatin synthesis in these growing forms prompted a combined cytological and chemical study. Growth was followed by phase contrast and by Feulgen stains, as well as by lipide phosphorus, nucleic acid, and protein analyses. In slide cultures, growth and compression led to monstrous flattened forms with readily visible, but coalescent nuclear structures. In fluid cultures, the protoplasts grew as phase dense spheres. Orderly reproduction of apparently discrete nuclear bodies was observed during the initial hours of spherical growth, but in older cultures, the chromatin arrangement tended to be more haphazard and was influenced by the concentration of Mg ions. In the same medium, protoplasts free of lysis showed a linear rise in optical density, while vegetative cells exhibited an exponential increase. However, protoplasts were able to synthesize DNA at the same rate as vegetative cells, but their increase of RNA was always less. Thus, as they grew, the ratio RNA/DNA fell. The lipide P increased in proportion to the expanding surface. With growth and lysis, large amounts of water-insoluble slime accumulated. Analyses indicate it to be a phospholipoprotein material containing some RNA.  (+info)

Studies on the origin of bacterial viruses. I-IV. (69/655)

I. The Incidence of Phage-Producing Cells in Various B. megatherium Cultures Analyses of small samples containing a few cells each show that lysogenic B. megatherium produces phage particles in groups of from 10 to 1000 depending on the megatherium strain and the culture medium. These groups probably correspond to the number of particles produced by a single cell. The proportion of such phage-producing cells varies from <1 x 10(-10) to about 1 x 10(-2) depending on the megatherium strain and the culture medium. If a culture produces two types of phage, the different types usually appear in separate samples. If mixed samples occur, the number of such samples is about what would be expected for the probability that two separate groups would appear in one sample. This result indicates that the appearance of a distinct phage type is the result of a change in the bacterial cell rather than a change in a phage particle, since in the latter case a mixture of the two types would result. II. The Effect of Ultraviolet Light on the Incidence of Phage-Producing and of Terramycin-Resistant Cells in Various B. megatherium Cultures Low intensity of ultraviolet light increases the proportion of both phage-producing cells and of terramycin-resistant mutants. The increase in phage-producing cells is greater than the increase in terramycin-resistant cells. High intensities of ultraviolet light cause practically all the cells of some B. megatherium strains to produce phage. The number of terramycin-resistant mutants cannot be determined under these conditions. The effect of ultraviolet light varies, depending on the megatherium strain and the culture medium. III. The Effect of Hydrogen Peroxide on the Incidence of Phage-Producing and of Terramycin-Resistant Cells in Various B. megatherium Cultures Low concentrations of hydrogen peroxide increase the number of phage-producing cells and of terramycin-resistant cells, concomitantly, from two to five times. High concentrations of hydrogen peroxide cause almost all the cells of some strains of megatherium to produce phage. IV. Calculation of the Incidence of Phage-Producing Cells The time rate of the appearance of phage particles in normal cultures, or in cultures treated with ultraviolet light or hydrogen peroxide, may be calculated by the same equations which predict the occurrence of terramycin-resistant mutants in B. megatherium cultures. These equations predict that the number of mutants will increase more or less in proportion to the concentration of mutagenic agent, so long as the mutation rate remains very small compared to the growth rate. As the mutation rate approaches the growth rate, there will be a very rapid increase in the proportion of mutants. This explains the striking effect of higher concentrations of mutagenic agents. In order to calculate the results after exposure to strong ultraviolet light or hydrogen peroxide, it is necessary to assume that the change from normal to phage-producing cell occurs without cell division.  (+info)

Studies on the origin of bacterial viruses. V. The effect of temperature on the terramycin-resistant and phage-producing cells of Bacillus megatherium cultures. (70/655)

The growth rates, the mutation frequency rate constants of the terramycin-resistant cells, the burst size of the phage-producing cells, and the ratio of phage to cells all have a temperature coefficient of about 2 from 20 to 35 degrees (micro = 9 x 10(3) calories), with a maximum at 40 degrees . The mutation frequency rate constant (or time rate constant) of the phage-producing cells increases from 20 to 45 degrees with a temperature coefficient of about 3 (micro = 2 to 3 x 10(4) cal.). The change in the values for the growth rate, mutation rate, and cell volume occurs in less than 1 hour, after the temperature is changed. The value for the burst size of phage-producing cells changes for 3 to 4 hours. Prolonged growth of megatherium 899 at 48 to 50 degrees results in the production of C + S phage, in place of T. Returning the culture to 25 degrees results in the production of small T phage.  (+info)

The effect of atebrin on bacterial membrane adenosine triphosphatases in relation to the divalent cation used as substrate and/or activator. (71/655)

The action of atebrin on purified adenosine triphosphatase (ATPase) from Micrococcus lysodeikticus was studied as well as on the membrane-bound and soluble ATPases from Escherichia coli and Bacillus megaterium. Atebrin inhibited the Ca(2+)-dependent activity of all these enzymes, and the inhibition was reversed by an excess of Ca(2+) ions. Kinetic studies carried out with the purified enzyme from M. lysodeikticus showed that the inhibition by atebrin was strongly cooperative, suggesting the complex nature of the process. On the other hand, atebrin stimulated the Mg(2+)ATPase activity of the M. lysodeikticus enzyme, displacing its adenosine 5'-triphosphate (ATP)/Mg(2+) optimum ratios, but inhibited the Mg(2+)-ATPase activity of E. coli provided that ATP was in excess over Mg(2+), i.e., that the ATP/Mg(2+) ratio was higher than its optimum. These results suggest that divalent cations influence the bacterial ATPases in different ways depending on the type of divalent ion and/or enzyme. The effect of atebrin on bacterial ATPases may reflect those differences, and its complex mechanism of action might be related to the existence of more than one site for divalent cations and/or distinct conformational states in these enzymes.  (+info)

Inhibition by antibiotics of the growth of bacterial and yeast protoplasts. (72/655)

Shockman, Gerald D. (Temple University School of Medicine, Philadelphia, Pa.) and J. Oliver Lampen. Inhibition by antibiotics of the growth of bacterial and yeast protoplasts. J. Bacteriol. 84:508-512. 1962.-The characteristics and requirements for growth of bacterial (Streptococcus faecalis) and yeast (Saccharomyces cerevisiae) protoplasts were established and the effect of a variety of antibacterial and antifungal antibiotics determined. A clear differentiation was obtained between such inhibitors of bacterial cell wall synthesis as penicillin and cycloserine, which did not prevent protoplast growth, and all others, antibacterial and antifungal, which inhibited protoplasts and intact organisms at the same range of concentration. Novobiocin, previously reported to inhibit bacterial wall synthesis, was also effective against a reaction(s) essential to the growth of S. faecalis protoplasts. The antibacterial action of streptomycin, neomycin, and kanamycin was essentially eliminated by the high salt concentration needed to maintain the protoplasts. Removal of the cell wall did not significantly increase antibiotic susceptibility of a resistant species. Protoplasts of Bacillus megaterium were insensitive to the antifungal agent, nystatin, and did not bind it to any detectable degree. Thus, the yeast or bacterial cell wall does not appear to play a major role in determining relative antibiotic susceptibility by masking internal sensitive target sites. A variety of antifungal antibiotics tested on the growth of log-phase yeast cells failed to produce osmotically fragile forms.  (+info)