- Volume 1, Issue 1, 1947

SUMMARY: A method of isolating species of Dictyosteliaceae from soil and other substrates is described.

Of ninety-three different strains of bacteria tested as food for Dictyostelium giganteum and D. mucoroides, some were readily or slowly but completely eaten, others were partly eaten and the rest were inedible. No correlation between the edibility of the bacteria and the formation of normal fruiting bodies could be found. More Gram-negative than Gram-positive strains were edible, and non-pigmented bacteria proved more suitable than pigmented bacteria for the normal development of Dictyostelium spp.

Values of pH between 4·1 and 8·9 had no effect on the abundance or on the types of fruiting bodies produced in either D. giganteum or D. mucoroides when suitable strains of bacteria were supplied as food to the myxamoebae on non-nutrient agar.

The maximum dimensions and the form of sorocarps and occasionally the colour of the sori were influenced by the type of bacteria used as food supplies. The influence of the bacterial food supply on the classification of Acrasieae is discussed and one new species (D. giganteum) is described.

Species of Dictyostelium are frequently present in arable soils in Great Britain. The common occurrence of Dictyostelium spp. in soils, which have been unmanured or treated with artificial fertilizers only for 100 years or more, disproves the belief that Dictyostelium spp. are dung organisms.

SUMMARY: A study of the life cycle of four sporing Actinomycetes by Robinow’s methods for the demonstration of Feulgen-positive chromatinic structures and of bacterial membranes, reveals two phases of growth in these organisms differing markedly in their morphological structure. These are: the primary or substratum mycelium which, by a special process, produces characteristic cells called ‘initial cells’, and the secondary or aerial mycelium which arises from the initial cells. The nuclear structures of the secondary mycelium undergo a division by which small rod-or dumbbell-shaped structures arise. Two of these appear to fuse, forming the round spore nucleus which, together with cytoplasm and enclosing membrane, represents the spore. The spores in their turn reproduce the primary mycelium.

SUMMARY: Myxococci are distinguished from other bacteria by the complete lack of a cell membrane as well as of transverse septa. Even the microcyst is enclosed by an outer layer which differs from a bacterial cell wall. In cytological character the young stages in the life cycle resemble other bacteria in so far as they contain two to four small nuclear structures or ‘chromosomes’ arranged transversely in the cell and dividing longitudinally. Older organisms about to form microcysts differ; they contain two fairly large nuclear structures which fuse to form a round chromatinic body. At the same time the cell shortens until a round organism containing one large, round, darkly staining nuclear body is formed. This ‘fusion cell’ can be compared to a zygote though it is not yet the resting cell of the species. The fusion cell becomes oval, its nucleus divides into two, and its outer layer becomes tough and dense. Thus the microcyst is formed. When it germinates its outer layer disappears, and the cell is transformed by elongation into the young vegetative organism.

The characteristic dry powdery appearance of the aerial mycelium of actinomycetes and the difficulty of wetting the constituent spores appear to be due to lipid substances in their outer walls. These substances are removed by fat solvents, and wetting agents, destroyed by alkali and are probably glyceride in nature. A staining with Sudan IV in ethanol clearly distinguishes the lipid-containing aerial mycelium from the vegetative mycelium.

SUMMARY: When first isolated on soil extract agar, soil actinomycetes consistently produce aerial spores in surface colonies. They retain this property when maintained in sterile soil, or when grown on washed suspensions of common soil bacteria, living or dead, in a water agar medium. In soil, when the composition, moisture content and temperature are kept constant, the initial stimulus towards the production of aerial mycelium is free access of air: the quantity and nature, vegetative or sporogenous, of the inoculum, and, within a broad range, the pH of the soil are of minor importance. Once growth is established, the next most important factor stimulating sporulation in the soil is also physical, namely dehydration. In natural and sterilized soils of different origins, and in a ‘Synthetic’ soil containing 250 p.p.m. of nitrogen as nitrate, the modes of growth of different actinomycetes strains are similar, and generally uncharacteristic of their species.

SUMMARY: By a method for determining the free amino-acid content of bacterial cells, Streptococcus faecalis (Lancefield Group D) was found to have free lysine, glutamic acid, ornithine and histidine in its internal environment, the amount depending to a certain extent upon the growth medium. The internal lysine and glutamic acid are unable to diffuse out of the cells when these are suspended in water or suitable salt solutions.

When the cells are grown in a medium deficient in amino-acids, the internal environment is also deficient and those cells can be used to study the conditions governing the passage of certain amino-acids into the cell. Lysine enters the cell by diffusion, probably passing the cell wall in the isoelectric state. Glutamic acid, glutamine and histidine cannot pass across the cell wall unless energy is supplied by some exergonic metabolism such as the simultaneous fermentation of glucose.

Under equilibrium conditions the internal concentration of free lysine or glutamic acid within the cell is markedly greater than that outside; the lower the external concentration, the higher the concentration difference across the cell wall.

Glutamic acid inside the cell can pass out into the external environment if fermentation is taking place. The final equilibrium conditions are the same whether the glutamic acid is entering or leaving the cell. Lysine cannot diffuse freely out of the cell, but outward migration takes place if fermentation occurs simultaneously. The uptake of lysine by deficient cells is decreased by the presence of glucose and this effect is, in turn, partially abolished by the uptake of glutamic acid in the presence of glucose.

SUMMARY: Treatment of Streptococcus faecalis cells containing high internal concentrations of lysine and glutamic acid with tyrocidin, Aerosol O.T., cetyltrimethylammonium bromide or phenol resulted in loss of the internal amino-acids. The substances used affected the cell wall so that the internal amino-acids leaked into the external environment; the rate of leakage was followed by a manometric method. The lytic action of tyrocidin, cetyltrimethylammonium bromide, Aerosol O.T., and phenol is sufficient to explain the disinfecting action of these substances.

SUMMARY: Sixteen Gram-positive organisms (including three yeasts) were able to assimilate glutamic acid and lysine from the external medium and to concentrate these amino-acids in the internal environment, while eleven Gram-negative organisms were unable to do so.

SUMMARY: Six antigenic components have been identified in toxic filtrates from Clostridium oedematiens, which hage been designated α, β, γ, δ, ε and ζ.

α is the classical lethal toxin of Cl. oedematiens and β and γ are haemolytic lecithinases, β being certainly necrotizing; δ and ζ are haemolytic, δ being oxygen labile; and ζ is probably responsible for pearly layer formation. Type A strains of Cl. oedematiens produce α, γ, δ and ε; type B stFins α, β and ζ; type C strains produce none of these components when examined by our methods. Two strains of Cl. haemdgticum produced the β lecithinase.

By methods based on certain characteristic properties of these six antigenic components, ‘oedematiens’ antisera can be tested for the corresponding antibodies.

In the identification of the various types of Cl. oedematiens, methods based on the properties of the β, γ and ε components give more consistent and clear-cut results than those depending on morphology, colonial formation or fermentation reactions.