adenine in their phenotype were isolated and the block in the purine pathway determined by enzymic activity of preparations obtained from the individual strains. The adenine-dependent mutants could be classed into two groups: one group was of strains devoid of any adenylosuccinate synthase (EC 6.3.4.4) activity; the presence of adenylosuccinate lyase (EC 4.3.2.2) activity was not detected in the strains of the other group. In these latter strains a single gene locus controls the two enzyme activities involved in the purine pathway, as established for other organisms.None of the adenine-dependent strains was capable of killing mice although they were given a toxic dose of adenine at challenge. Reversion to prototropky restored full virulence. The lack of proliferation of the adeninedependent bacteria in the host could not be explained simply by a shortage of available adenine in the body of the mouse, since the adenine intake provided a certain concentration of this base at the inoculation site, in the peritoneal cavity, and in the blood stream. In spite of the fact that adeninedependent mutants were producing both of the known aggressins, namely capsule and toxin, they were not capable of invading the blood stream or of multiplying there. It is assumed that something essential for invasion of the host was not produced by adenine-dependent mutants. The lack of this hypothetical factor rendered these organisms highly vulnerable to the defence mechanism of the host. In contrast to the adenine-dependent mutants, purine auxotrophs blocked either in the early part of the purine pathway or in the conversion of xanthylic acid to guanylic acid were found to grow readily in the body of the mouse, even in the absence of an exogeneous supply of purine bases. It is suggested that purine bases needed by these mutants for their growth might originate from an influx of purines from tissues damaged by the bacteria.
SUMMARY : Megacin however highly bactericidal for sensitive organisms was not adsorbed by them. Its bactericidal action was markedly dependent on temperature. The viability of organisms exposed to megacin at 0' was not affected. When megacin was added to exponentially growing Bacillus megatm'um there was cessation of growth followed by a gradual decrease in turbidity of the culture. The decrease in turbidity was, however, not associated with a total lysis of individual organisms; rather it. was the consequence of the escape of the dense intracellular material from the organisms. Intracellular components, i.e. substances which absorbed in the ultraviolet region escaped from the bacteria into the medium while cell wall remained essentially intact. When B. megaterium suspended in a medium containing lactose was exposed to megacin, p-galactosidase appeared on the surface of bacteria.Protoplast preparations made from Bacillus megaterium and Mimococcus aurantiacus (both sensitive to megacin) were converted into ghost-like structures on the addition of megacin. On the other hand, protoplasts made from insensitive species resisted megacin. Observations indicate that megacin causes a radical change in the osmotic barrier of sensitive organisms by attacking the cytoplasmic membrane. Data available suggest that megacin is either an enzyme which breaks down the osmotic barrier of sensitive cells, or is a substance capable of activating the intrinsic enzymes of cells which lead to an autolysis of cytoplasm.
SUMMARY: Two hundred strains of Bacillus megatmiurn recently isolated from soil were tested for an antagonistic effect on a phage-resistant strain of the same species. Fifty-one strains gave a zone of inhibition on a lawn of the indicator strain. This effect was increased by a small dose of ultraviolet radiation which also caused 41 other strains to show an antagonistic effect. Sixteen strains which were completely lysed after U.V. irradiation also produced confluent lysis of the indicator strain. When grown in liquid media, these strains gave irregular growth curves owing to partial lysis during the exponential phase. Lysis was almost complete when such cultures were incubated after exposure to small doses of U.V. radiation. Lysis was always associated with accumulation of the antibacterial principal previously named 'megacin'. Irregular growth in liquid media and production of megacin were strictly correlated. However, only 2 megacinogenic strains were lysogenic and liberated phage. Populations of megacinogenic strains were examined by replicaplating for the presence of non-megacinogenic mutants. Spore suspensions of 4 megacinogenic strains contained non-megacinogenic mutants in various proportions depending on the strain and the particular sample. Non-megacinogenic mutants could not be made to lyse by exposure to U.V. radiation ; did not produce any antibacterial effects ; and all showed normal patterns of growth in various liquid media.
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