- Volume 2, Issue 1, 1948

Summary: Giant amoeboid organisms may be isolated from soil and other materials by the use of suitable edible bacteria supplied on a base of non-nutrient agar.

Leptomyxa reticulata is widely distributed in the soils of Great Britain. The common occurrence of this organism in soils which have been unmanured or treated with artificial fertilizers for 100 years or more proves that it is a soil inhabitant.

Degrees of pH between 4·1 and 8·7 had no effect on the abundance of growth when a suitable bacterial strain was supplied as food on non-nutrient agar.

Ninety-two very varied strains of bacteria tested as food for L. reticulata varied greatly in edibility. Bacteria producing red, violet and blue pigments were mostly inedible. There was no correlation between Gram-staining and edibility.

Certain bacterial strains induced the formation of cysts by L. reticulata. This property was not correlated with their edibility.

SUMMARY: The effect of pH over the range 5–9 on the growth of Bacterium coli with a constant food supply was studied at 20 and 30°. Total and viable counts were made and growth curves constructed. To discover the effects of starvation, sampling was continued after stopping the food supply.

The total count always substantially exceeded the viable. Each growth curve showed an ‘initial phase’ of varying daily increment in cell numbers merging into a ‘steady phase’ of roughly constant increment, which continued as long as food was supplied. Low pH slightly shortened the initial phase, low temperature greatly prolonged it. In the early initial phase development was slow at pH 5, but later became exceedingly rapid. Altogether, the conversion of the food supplied into (total) bacterial cells was best effected in conditions of low temperature and low pH, low temperature being the more important. These conditions also favoured high viable counts, and consequently smaller non-viability indices.

During starvation the apparent total counts declined, except at 30° and pH 5, when a steady increase occurred. Higher pH and lower temperature led to faster rates of decline. Viable counts remained approximately constant at pH 5, but otherwise the numbers declined.

SUMMARY: Pantothenic acid was essential for the growth of a strain of Lactobacillus plantarum. It increased acetylcholine formation during growth and in washed suspensions of pantothenate-deficient organisms. Added pantothenic acid did not affect the glucose utilization or lactic acid formation by the pantothenate-deficient organism in washed suspension.

The co-enzyme concerned in acetylation of choline in brain and of sulphanil-amide in liver has been shown to contain pantothenic acid (Lipmann, Kaplan, Novelli, Tuttle & Guirard, 1947). At the suggestion of Dr Lipmann, pantothenic acid was tested as a factor in the synthesis of acetylcholine by a strain of Lactobacillus plantarum. It proved to be essential both for acetylcholine formation and for growth (Stephenson & Rowatt, 1947). This paper contains a more detailed examination of the phenomenon.

Summary: Three main antigens were found to be variously distributed amongst strains of Pseudomonas pyocyanea. The serological behaviour of the strains studied depended on the presence and quantity of these antigens. It was not possible to distinguish between flagellar and somatic antigens, but those found were probably somatic.

Amongst the peculiarities of serological behaviour of bacteria in this species the most striking was a complete loss of agglutinability on moderate heating, which left the antigenic activity unimpaired.

Summary: The use of plate glass sheets carrying twenty-four cylinders in place of Petri dishes for the biological assay of streptomycin by the cylinder-plate method initially led to large assay errors. The substitution of cavities for cylinders, of a single layer of agar for two layers, one sterile and one inoculated, of the four-point assay design for ‘reading off the curve’, and of an optical projection method of measurement diminished the fiducial limits of error of an assay to 80–125% (P = 0·95).

Over the range of concentrations 0·1–100·0 units streptomycin/ml. the deviations from linearity of the graph of zone diameter against the logarithm of the concentration were very small.

Variations in thickness of the agar layer and in the intensity of inoculation had a marked effect on zone diameter.

An 8 × 8 Latin square lay-out reduced the internal error of an assay to 91–110% (P = 0·95), and with this increased accuracy a bias in the results was revealed arising from the time interval between filling successive cavities on the plate. This time effect was eliminated by the adoption of an appropriate order of filling, with a quasi-Latin square lay-out. The form of the assay finally adopted had fiducial limits of error, estimated both internally and externally, of about 95–105% (P = 0·95).

SUMMARY: Soil micro-organisms have been counted by a new technique whose essential feature is the suspension of measured amounts of soil in a molten agar gel from which small drops are removed and allowed to solidify as thin films on a haemocytometer slide of known depth. The instantaneous gelation of the agar ensures the fixation of the soil constituents in their original distribution. The films are dried and stained in a solution of acetic-aniline blue and permanent preparations made by subsequent dehydration in ethanol and mounting in euparal. If the suspension is of known dilution, since films of a definite volume contain a known quantity of soil, differential counts of a measured area of film will yield a quantitative estimate of soil micro-organisms.

The distribution of bacteria per microscopic field was found to be complex. The frequencies of bacterial colonies and of pieces of fungal mycelium form a Poisson series; those of the number of bacteria per colony form a logarithmic series; and those of the total number of bacteria per field fall into a negative binomial distribution.

The method appears to be capable of modification by the use of selective nutrient media for determining the quality of the microflora and possibly the percentage viability of the organisms present.

Summary: Penicillium notatum gives high yields of spores on media containing carbohydrates, ammonia and an organic acid such as citric, tartaric, or succinic acid. The media are similar to those which are good for the production of penicillin, but the choice of organic acids is less restricted.

Of physical factors influencing the yield of spores the most interesting was variation in the volume of medium. Within certain limits the number of spores produced depended almost entirely on the volume of the medium and not on the surface area; i.e. the yield of spores/unit area depended on the depth of the medium. An increase in the concentration of metabolites above normal level did not greatly increase the yield of spores, and the addition of further nutrients to a previously used medium gave only a small second crop. The production of spores therefore appeared to be limited by the accumulation of toxic substances in the medium.

Summary: A non-sporulating form of Streptomyces griseus occurred spontaneously in culture. It appears to be a true variant of the species. Ultra-violet irradiation stimulated the variation. The variant was readily isolated on media containing relatively large amounts of organic nitrogen, but capable of propagation upon very simple media. The fact that the variant can be stabilized throws some doubt upon the validity of the present basis for classification of the actinomycetes.

Summary: In those members of the genera Bacterium and Bacillus studied, the constituent bacteria of Smooth cultures are typically unicellular, containing two chromatinic bodies. On division, a membranous septum is first formed, the bacillus subsequently dividing by constriction at this point.

The constituent bacteria of Rough cultures may comprise several cellular units, typically four, each containing a single chromatinic body and separated by membranous septa which, as growth proceeds, are transformed into true cell-wall septa, by the splitting of which the bacillus divides.

SUMMARY: Excellent cytological preparations may be made from growth of Leptomyxa reticulata on cover-slips on a film of agar.

The organism is multinucleate. Each resting nucleus contains a deeply staining mass, the nucleolus, which is surrounded by a clear zone in which chromatin material is scattered. There is always a definite nuclear membrane. The nuclei divide simultaneously by intranuclear mitosis and the whole process is completed in a short time. At prophase the dispersed chromatin granules aggregate and later assume a thread-like structure and enter upon the metaphase. The formation of the spindle can be seen at the beginning of the metaphase. No centrosomes are seen at any stage. During anaphase the chromosomes begin to separate and it is difficult to count their numbers. The nuclear membrane disappears at late anaphase. At telophase the daughter chromosomes fuse together, the connecting threads break and the daughter nuclei are formed.

Under suitable cultural conditions and on certain strains of bacterial food supply, multinucleate cysts are produced in clusters. The process of cyst formation is described.

The scientific names of organisms are the means by which one worker is able to relate his observations or opinions to those of others, and no one would benefit more than the microbiologist from an internationally acceptable and stable nomenclature. A large measure of agreement has already been reached on what constitutes an internationally acceptable name, but because appropriate and universally accepted names only reflect an agreed classification it will require much work by both systematists and experimental microbiologists before stability can be approached in many groups of micro-organisms. As a first step towards the goal microbiologists are urged only to use names which conform to international agreements because such usage makes for precision and at least does not hinder developments in classification. The purpose of this article is to advocate care in the use of names and to draw the attention of those who may wish to propose new taxonomic groupings or to change old names to certain requirements of the International Rules of Nomenclature. Also, systematists frequently feel obliged to make changes in the names of the groups of organisms which they study; changes which may at times seem arbitrary and unnecessary. A knowledge of the International Rules often enables the reasons for such changes to be more fully appreciated and sometimes allows a distinction to be made between name changes which are obligatory on all and those which need not be accepted at once, if ever, when they would disturb some long-established usage.

SUMMARY: Following the original inoculation of cotton rats with material from the spleen of a golden hamster containing Leishman-Donovan bodies, a number of serial passages were subsequently carried out in these animals. The parasite became rapidly adapted to the new host and a progressive infection resulted comparable with that in the golden hamster. Whereas death in the latter animal is the invariable sequel of infection, the cotton rat appears to be unaffected by the disease. The cotton rat thus provides a new and easily obtainable host for the study of experimental leishmaniasis in this country, including the chemotherapy of the disease.