- Volume 25, Issue 2, 1961
Volume 25, Issue 2, 1961
- Article
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The Action of Acriflavine on Brewers’ Yeasts
More LessSUMMARY: The absorption of acriflavine by strains of Saccharomyces carlsbergensis and S. cerevisiae occurred at approximately the same rate and extent and was greatest in the range pH 4–5. In this range, the proportion of respiration-deficient cells produced by acriflavine treatment was also maximal. Furthermore, under more alkaline conditions, the acriflavine exerted a pronounced toxic effect. At pH 4–5, the proportion of mutant cells produced was about 50 times greater in strains of S. cerevisiae than in those of S. carlsbergensis, while fewer cells were killed. With S. cerevisiae the production of mutants was rapid and in certain strains exposure for 1 hr. to 50 μg. acriflavine/ml. led to about one-third of the cells mutating, while after 4 hr., all the cells were respiration-deficient. In contrast, exposure of strains of S. carlsbergensis for 24 hr. at this concentration of acriflavine induced only about one-tenth of the cells to mutate. The mutants took up no measurable amount of oxygen when examined in Warburg respirometers. As compared with the parent cultures, there was no difference in the ability of the cells to utilize carbohydrates and to undergo flocculation.
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The Function of Glycerol, Cholesterol and Long-Chain Fatty Acids in the Nutrition of Mycoplasma mycoides
More LessSUMMARY: Mycoplasma mycoides var. mycoides requires for growth a number of preformed lipid precursors. Media containing glycerol, cholesterol, a saturated and an unsaturated fatty acid, defatted bovine serum albumin and an additional defatted serum protein fraction (Fraction C) can supply these requirements. Albumin is believed to function by binding fatty acids, and Fraction C by binding cholesterol. The requirement for a saturated fatty acid can be satisfied by myristic, palmitic, stearic or margaric acid, lauric acid being less effective. The requirement for an unsaturated fatty acid can be satisfied by oleic acid, linoleic and linolenic acids being less effective. Organisms incubated in a medium deficient in either glycerol, the Fraction C + cholesterol system, or oleate, but adequate with respect to all other nutrients, died rapidly. Death was accompanied by lysis. Death due to a deficiency of glycerol or of cholesterol was prevented either by the omission of uracil (an essential nutrient) or by addition of chloramphenicol. Death due to oleate deficiency was not prevented by the omission of uracil. Morphological changes which resulted from each of these deficiencies are illustrated by electron micrographs. The hypothesis is advanced that glycerol, cholesterol and long-chain fatty acids are all needed for the synthesis of an undetermined cell component which is necessary for the structural integrity of the cell, and that the synthesis of this is more sensitive to a deficiency of these nutrients than is the synthesis of cytoplasm.
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Glyceride Hydrolysis and Glycerol Fermentation by Sheep Rumen Contents
More LessSUMMARY: Microbial hydrolysis of triglycerides was observed when these were incubated anaerobically at 37° with sheep rumen contents. The extent of hydrolysis was variable, but was often considerable ( > 90 %) when linseed oil was used as substrate. The free fatty acids liberated Were analysed by gas chromatography and, as compared with the acids present initially in glyceride combination, they were less unsaturated because of microbial hydrogenation. Linolenic acid was particularly effectively hydrogenated. No synthesis of long-chain fatty acids took place during the incubations and, apart from the possibility that in some experiments a limited conversion of stearic acid to palmitic acid took place, there was no evidence of significant degradation of long-chain acids. Glycerol liberated during the hydrolysis was completely metabolized, in part to volatile fatty acids, largely propionic acid. No mono- or diglycerides were detected as intermediates in the lipolysis of triglycerides. Analysis of the contents of the rumen, abomasum and small intestine of each of two slaughtered sheep, one of which had previously been fed on a diet rich in linseed oil, showed that most of the total higher fatty acids present in each of these three portions of the alimentary tract was in the form of free acids. It is concluded that microbial lipolysis results in the pre-digestion of much of the lipids ingested by the sheep as part of its feed.
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The Isolation of Glycerol-Fermenting and Lipolytic Bacteria from the Rumen of the Sheep
More LessSUMMARY: Facultatively anaerobic bacteria appear to play little part in glycerol fermentation in the sheep rumen. Amongst the most important members of the glycerol-fermenting flora are strict anaerobes of the group Selenomonas ruminantium var. lactilyticas. Three isolates of a different group of strictly anaerobic curved Gram-negative rods, which hydrolyse linseed oil and tributyrin as well as fermenting glycerol, were obtained in numbers which suggest they are amongst the more important lipolytic bacteria in the rumen. The main product of fermentation of glycerol by the seleno-monads and the lipolytic bacteria is propionic acid, but other acids are also formed. The properties of these bacteria and some others isolated during the experiments are described. All the bacteria appear to be normal inhabitants of the rumen of sheep fed a number of different rations. The numbers of these organisms were not appreciably increased by feeding glycerol or triglycerides to the animals.
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The Isolation and Characterization of Bacteriophages from Listeria monocytogenes
More LessSUMMARY: The bacteriophages of Listeria monocytogenes have been studied with respect to isolation techniques and their use as diagnostic tools and as aids in epidemiological investigations. The occurrence of lysogeny was investigated in 123 strains isolated from human and animal sources throughout the world. Conventional procedures for isolation of phage were unreliable with Listeria since lysogenic strains did not always, by spontaneous lysis, release a detectable amount of phage. However, after exposure to ultraviolet radiation, such strains were induced to produce up to 107 plaque-forming particles/ml. Some strains which did not release phage produced substances after irradiation possibly analogous to colicines. The lytic spectrum of 11 phages against 149 strains of Listeria was studied and a system of classification, with five of these phages, was used to place 127 of these strains in 8 phage types. Nearly all of the untypable strains were rough, undergoing dissociation, or were lysogenic. Phage susceptibility appeared to be closely associated with the serological type of the strain, but showed no relation to the animal source or the geographical origin. These studies indicated that Listeria phages could be used as a means of generic identification and also as a substitute for or an adjunct to serological typing in epidemiological investigations.
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The Nutrition of a Lactobacillus acidophilus Variant Isolated from the Duodenum of a chick
J. E. Ford and M. RogosaSUMMARY: Allen, Stephens, Jaffe & Wakelam (1959) isolated a lactobacillus which they found to require a growth factor present in malt distillers’ dried solubles. We have identified the organism as belonging to the subgroup Thermobacterium Orla-Jensen. It was grown through many serial passages in a chemically defined medium containing thymidine, and had no residual indispensable requirement for unidentified nutrients.
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A phage, 𝜙χ, which attacks motile bacteria
More LessSUMMARY: A salmonella phage which attacks only flagellated bacteria (Sertic & Boulgakov, 1936b) has been studied. Tests with naturally occurring strains, and with artificial serotypes to which foreign H antigens had been transduced, have shown that sensitivity depends on the H antigen: bacteria with antigens of the g-complex are resistant, and with antigens l…, e,h, or Arizona 13, are sensitive only to appropriate host-range mutants. Tests with non-mo tile and motile variants of the same strains showed that paralysed (non-motile H) as well as non-flagellated bacteria are resistant and thus that the flagella must be active as well as of correct antigenic type. Where resistance was due to absence of suitable flagella, it was associated with impaired adsorption of phage. Removal of the flagella from a sensitive strain led to diminished adsorption; a similar result was obtained when the bacteria were artificially paralysed in various different ways. No adsorption to detached flagella was detected, probably because they were inactive. Adsorption of the phage led to immobilization and agglutination of the bacteria, probably by a direct effect on the flagella. Electron micrographs showed phage particles attached to flagella, and infection could evidently follow adsorption to distal parts of a flagellum. The genome of the infecting particle may perhaps reach the bacterial body by being injected into an active flagellum at the point of initial attachment, and then travelling inside the flagellum.
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Substances which Protect Lyophilized Escherichia coli against the Lethal Effect of Oxygen
More LessSUMMARY: The lethal effect of oxygen on Escherichia coli organisms freeze-dried from water may be partly abolished by the addition of certain compounds before lyophilization. Three groups of such protective compounds were found: (i) thiourea, some of its derivatives and analogues; (ii) sugars, especially monosaccharides and some of their derivatives; (iii) some simple inorganic salts. The protective action was not unequivocally correlated with reducing power. Certain reducing agents (e.g. sodium dithionite, cysteine, reduced glutathione) even enhanced the lethal effects of oxygen.
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The Oxidase Reaction as a Taxonomic Tool
More LessSUMMARY: The oxidase test of Kovacs (1956) was applied to 1660 strains of various genera, of which 210 gave a positive reaction and 64 gave a delayed positive reaction. Members of the Neisseriaceae and Pseudomonadaceae were generally oxidasepositive, whereas members of the Enterobacteriaceae and, with few exceptions, Gram-positive organisms, were oxidase-negative; equivocal results were obtained in the Brucellaceae and the genus Bacillus. Kovacs test is simple and quickly performed, but very sensitive. Some taxonomic implications of the results are discussed.
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Inhibition of Enzyme Formation Following Infection of Escherichia coli with phage T2r+
A. P. Levin and K. BurtonSUMMARY: The synthesis of aspartate carbamyl transferase (ureidosuccinic synthetase), of dihydroorotic dehydrogenase and of alkaline phosphatase by a uracil-requiring strain of Escherichia coli, when the organisms were suspended in a minimal medium lacking uracil, was followed subsequent to infection of the cells with bacteriophage T2r+ or with ghosts of the bacteriophage particles. The results were compared with the synthesis of these enzymes in uninfected cells. Following infection, the formation of all three enzymes was halted. Supplementation of the medium with casein hydrolysate and tryptophan or with 0·0lm-Mg++ + 10−3 m-spermine did not prevent the inhibition caused by bacteriophage infection.
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The Action of Tetanus Toxin in Frogs
More LessSUMMARY: The development of tetanus intoxication in the frog is dependent on the environmental temperature being above about 15°. The incubation period and time to death become shorter as the environmental temperature is raised. Cooling below about 15° prevents both the fixation of the toxin and its action after fixation but does not increase the speed at which the toxin is destroyed or excreted. The absorption of the toxin after injection into the dorsal lymph sac is not prevented by cooling. It is possible to produce local tetanus in frogs by the intramuscular injection of tetanus toxin, but the dose needed for this is very critical. In most cases either generalized tetanus develops or there are no signs of intoxication. However, local tetanus can regularly be produced when the toxin is given intramuscularly to frogs partially protected from generalized tetanus by an injection of tetanus antitoxin given via the dorsal lymph sac. The local tetanus so produced does not progress to involve the opposite limb. The muscular spasm is abolished by cutting the motor nerve or by general anaesthesia. Tetanus toxin appears to act on the central nervous system of the frog in the same manner as in mammals. However, frog brain tissue does not neutralize tetanus toxin in low concentrations as does mammalian brain tissue, but concentrated tetanus toxoid gives immediate protection to frogs in the same way as it does in mammals.
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