- Volume 9, Issue 1, 1953
Volume 9, Issue 1, 1953
- Article
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The Establishment of Serologically Identifiable Strains of Rhizobium trifolii in Field Soils in competition with the Native Microflora
More LessSUMMARY: Field trials were made at thirteen centres in varied localities to test whether a strain of clover Rhizobium used as a seed inoculum in the field could establish itself in the crop in competition with the native strains already present in the soil. Each experiment comprised four sets of plots, one uninoculated and the other three each sown with seed inoculated with a different strain of Rhizobium.
The difficulty in identifying a strain re-isolated from a nodule was met by using as inocula strains whose antigenic composition made them readily identifiable by agglutination tests. From each plot, twenty-five nodules were selected, and isolates from these tested against selected antisera. This method of identification enabled the percentage of nodules produced by each inoculant strain to be ascertained. Strains differed in their ability to establish themselves in the field: a suitable strain gave rise to 50% or more of the nodules. In sand culture competition between pairs of inoculant strains was not related to their ability to establish themselves in the field, but each strain whose establishment was superior also showed competitive dominance on at least one date of sampling.
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The Fermentation of Malt Extract by an Osmophilic Yeast
More LessSUMMARY: The fermentation of malt extract by the osmophilic yeast Saccharomyces rouxii Boutroux is described. It is found that the limiting factor determining whether an extract will ferment or not is its relative humidity, the critical level of which is about 73%. If the relative humidity is raised above this level, either by raising the moisture content or by lowering the proportion of sugars in the total solids, the extract can be fermented by S. rouxii.
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A Probable Growth Cycle in Bacillus megaterium
More LessSUMMARY: The sequence of events which occurs as Bacillus megaterium grows and divides is shown to involve cells with fusion nuclei and cells which undergo an apparently sexual process. An account is also given of the part played in cell division by granules associated with the cell membrane. These resemble mitochondria in that they are centres of intense oxidative activity, and they are shown to be related to growing points which have been reported in other organisms.
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Radiation-induced Instabilities in Streptomyces
More LessSUMMARY: A variety of heritable changes affecting colony morphology and colour are induced in a Streptomyces sp. by exposure of the spores to ultraviolet and gamma rays. Most of the changes are associated with instabilities which give rise to further variation during colony growth and spore formation. The instabilities persist indefinitely in most lines of descent and give rise to characteristic proportions of new variant types each having its own pattern of instability. The ultraviolet dose/effect curve shows the familiar peak and decline found for mutations in many other organisms. The present changes, however, differ from the gene mutations previously studied in that they can be induced with much greater frequencies (30-60% of the colonies being affected), and that gamma rays are as effective or more so than ultraviolet irradiation. This suggests that the initial changes, and perhaps subsequent ones as well, might be more of the nature of the chromosomal rearrangements, rather than of the gene mutations, of higher organisms. Similar instabilities arise spontaneously but with a much lower frequency.
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Interrelationships between Amino -acids in the Growth of Coliform Organisms
More LessSummary: Three hundred and fifty-six strains of Bacterium coli, which were capable of growing on a simple salt medium containing ammonia as sole nitrogen source and glucose, were tested for inhibition of growth by added amino-acids. Inhibitions by certain amino-acids were found, and each inhibition could be prevented by the simultaneous presence of one or more other amino-acids. It was not possible to correlate these inhibitions with any other biochemical property of the strains. There was, however, a remarkably high proportion of serine-inhibited strains amongst those which had been isolated from cases of infantile gastro-enteritis.
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The Cultivation and Metabolism of Oligotrich Protozoa from the Sheep’s Rumen
More LessSummary: Suspensions of the oligotrich protozoan, Metadinium medium, were extracted from whole rumen contents by allowing the large protozoa to settle out from the bulk of the rumen liquor and concentrating by pouring off the supernatant. The settled protozoa were separated from the associated rumen debris by incubation with maltose, when a bacterial fermentation set in with a vigorous production of gas which carried most of the rumen debris to the surface for removal by gentle suction. After repeated washing of the protozoa by resuspension in buffer and removal of the supernatant, M. medium was cultivated on powdered cotton-wool (0·5 %) and powdered hay (0·05 %) in buffer at pH 6·8. These oligotrich protozoa remained alive and dividing for 12 days. A species of Entodinium, concentrated from rumen liquor and washed by centrifugation, after the larger protozoa had settled out, was kept alive for 12–14 days under similar conditions in the presence of rice starch grains instead of powdered cotton-wool. Streptomycin (560 µg./ml.) was used to prepare cultures of protozoa which were bacteriologically sterile when tested by streaking agar plates containing yeast extract, starch and glucose or cellobiose. Under these conditions, Entodinium spp. disappeared within 24 hr. and M. medium in 3 or 4 days. This suggests that these organisms are dependent on bacteria for some of their metabolic processes. It is concluded that the species of Metadinium studied here contained symbiotic cellulolytic bacteria which were destroyed by streptomycin, but that the protozoa continued at least for some time to draw on their polysac-charide reserves after treatment with the antibiotic. Rumen oligotrichs may be of use to the sheep by acting as ‘reservoirs’ of polysaccharide and so preventing rapid bacterial breakdown. The relationship between the protozoa and the ruminant is considered to be a true symbiosis.
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The Release of Soluble Constituents from Washed Cells of Pseudomonas aeruginosa by the action of Polymyxin
More LessSummary: The addition of polymyxin E to washed cell suspensions of a strain of Pseudomonas aeruginosa caused a release of materials which had absorption maxima at 260 mµ., pentose and phosphate from the cells. This release did not occur at 2 and in this respect differed from the leakage resulting when cells were suspended in distilled water or were treated with cetyltrimethylammonium bromide (CTAB). There was an optimum concentration of polymyxin for maximum release of cell constituents, higher concentrations inhibiting the release. A similar release of cell constituents, which was prevented at low temperatures, occurred when cells were suspended in buffer at pH 53. Morphological changes resulting from polymyxin treatment have been studied using the electron microscope.
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The Vi Type-determining Phages carried by Salmonella typhi
More LessSummary: The properties of the latent phages present in twelve of the thirty recognized Vi-phage types of Salmonella typhi are described. The isolation and characterization of these phages presented great technical difficulties which have been partly overcome.
Nine of the latent phages were shown to control Vi-phage type specificity in the lysogenic strains that carry them. The remaining three phages have not so far been demonstrated to have type-transforming properties.
The latent phages are O phages, as indicated by their lytic action on the Vi-negative Sal. typhi strain O 901 and on Sal. gallinarum. By cross-neutralization tests the twelve phages are subdivided into four serological groups, one of which shows a considerable degree of antigenic community with an anti-O phage known to attack many salmonella species belonging to different O groups. No serological relationship was found between any of the latent phages and Vi-phage II.
The Vi-phage type of lysogenic strains of Sal. typhi is an expression of a resistance pattern dependent on the carried phages. These phages seem to confer resistance against unadapted Vi-phage II and simultaneously to induce phenotypic modifications in it to yield specifically adapted Vi-phage preparations.
Artificially prepared Vi-phage types of the typhoid bacillus, produced by the treatment of susceptible strains with type-determining phages, appear to be as stable as the corresponding Vi-types found in naturally occurring lysogenic strains. The fact that world-wide experience with the Vi-phage typing technique over many years has proved its epidemiological reliability suggests that the chances of the typhoid bacillus encountering type-changing phages under natural conditions are remote.
It is shown that the recently proposed method of typing bacteria by identifying the phages they carry is unsuitable for application to Sal. typhi.
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The Utilization of Nitrate Nitrogen by the Azotobacter
More LessSummary: Four types of utilization of nitrate nitrogen were observed with fourteen strains of the azotobacter. These were:
(a) Those which utilize NO− 3 -N with no or only a short lag; three strains of Azotobacter vinelandii, a stock culture of A. chroococcum C-77, and seven strains of A. chroococcum freshly isolated from soil were in this group;
(b) A single strain, a stock culture of A. chroococcum C-44, which uses NO− 3 -N only when conditions permit selection of a mutant capable of using this form of nitrogen;
(c) A single strain, A. indicum 10, which uses NO− 3 -N very slowly in air and in which NO− 3-N accumulates;
(d) A single strain, A. agile 4·4, which does not use NO− 3 -N. Certain other morphological and physiological differences between strains of A. vinelandii and the strain of A. agile 4·4 are pointed out which suggest that the question of the recognition of these strains as a single species be re-examined.
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Relation of Bacteriophage Pattern to some Biological Properties of Staphylococci
More LessSummary: Representative coagulase-positive staphylococci that had been examined for their production of diffusible antigens, α- and β-haemolysins, fibrino-lysin and pigment, were typed by bacteriophage. Among strains from human sources there was no significant association between the phage group and the other properties. Strains of staphylococci obtained from animals seemed, however, to form a different biological group from those from human beings.
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Micromethod for the Methyl Red Test
More LessSummary: A micromethod for the methyl red (mr) test was worked out for suspensions of bacterial cells. The most important factors in the test are (1) the density of the cell suspension; (2) the ratio of glucose to buffer concentrations. Adaptation of the cells to glucose is essential for the success of the test, and cells from glucose-free media are not satisfactory. At the optimal glucose: buffer ratio Bacterium coli and Klebsiella aerogenes suspensions have different effects on the final pH value attained in the system.
Because the mr microtest is dependent on a fine balance between glucose and buffer concentrations, and is so greatly affected by even twofold differences in cell concentration, it is not really suitable for routine work in the characterization of bacteria.
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Identification of Strains of Streptococcus pyogenes of Types 5, 11, 12, 27 and 44 by the Precipitin Test for the T Antigen
More LessSummary: Strains of Streptococcus pyogenes belonging to Types 5, 11,12, 27 and 44 share a minor T antigen. In addition, there are three major T antigens in this set of types, one in Type 11, one in Type 12 and the third common to Types 5, 27 and 44.
T antigen, prepared by Pakula’s method, is a satisfactory fraction for absorbing the antibodies from serum, the advantage being that very little serum is lost with each absorption because the volume of T antigen required is so small. The Pakula method of extraction of the T antigen can also be satisfactorily used in routine typing. Type 11 strains can be definitely identified by the T precipitin test, and this test can also be used for identifying Type 12 strains that give no reaction with Type 12 anti-m sera. There are some strains which have agglutination patterns of the series 5, 11, 12, 27 and 44 but which give no precipitation with the T antisera. It may be that in these the major T antigen has not been recognized.
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Influenza Virus Multiplication in the Chick Chorioallantoic Membrane
More LessSummary: A description is given of techniques used for studying influenza virus infection of the allantoic and chorionic surfaces of the chick chorio-allantoic membrane. It was possible to infect one surface of the membrane at a time and to show that the two layers behaved independently and reacted differently. In contrast to the allantoic layer, the chorionic cells appeared to support only a single cycle of multiplication. This conclusion is based particularly on the small rise of infectivity which occurs following chorionic inoculation of virus, and on the proportion between the amount of virus inoculated and the yield of soluble antigen. Some evidence is presented which suggests that the elementary bodies are less readily released from chorionic cells than from the allantoic cells.
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Interference in the Chick Chorion
More LessSummary: Experiments were carried out in an attempt to demonstrate in the chorionic cells of the chick chorio-allantoic membrane some of the interference phenomena with influenza viruses which are readily demonstrable in the allantoic cells. When a mixture of PR 8 and Lee viruses was inoculated on the chorion, no interference occurred; on the contrary, the soluble antigen titres for A and B antigen showed a highly significant positive correlation in individual eggs. Influenza virus, partially inactivated by heat or ultraviolet irradiation and shown to produce ‘auto-interference’ in the allantoic cells, showed no such effect when inoculated on the chorion; on the contrary, a phenomenon which may be similar to that described under the name ‘multiplicity reactivation’ was observed. Influenza virus completely inactivated by heat or by ultraviolet irradiation caused pronounced interference with the multiplication of large inocula of virus in the allantoic cavity; no interference was found when the same materials were inoculated on the chorion. However, there is some evidence to show that irradiated virus caused slight inhibition of the increase in infectivity which results when small doses of influenza virus are inoculated on the chorion.
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Antigenic Relationships of Swine Influenza Virus
More LessSummary: Antigenic comparisons of six strains of swine influenza virus with three strains of human influenza A virus were made by the agglutination-inhibition technique. The strains were also compared in regard to inhibition by normal sera, rate of elution from red cells, pathogenicity for mice, and other properties. All swine strains were significantly different from human strains. Four American swine strains formed a fairly homogeneous group, but were less closely related to two strains recovered in the United Kingdom. The findings are briefly discussed in terms of the relationship between human and swine influenza.
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Mycobacterium tuberculosis var. muris
More LessSUMMARY: The valid name for the acid-fast bacillus which causes tuberculosis in voles is Mycobacterium tuberculosis var. muris Brooke.
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