- Volume 37, Issue 1, 1964

Summary: The cultural, physiological and serological characters of new Pediococcus isolates have been studied. Suggestions are made for the amendment of the definition of the genus Pediococcus. The genus is considered to contain the four species P. cerevisiae, P. parvulus, P. damnosus and P. halophilus.

Summary: The fraction of bacteria of a proline-requiring auxotrophic strain of Escherichia coli strain B which was able to originate macrocolonies on a defined nutrient medium after exposure to γ-rays under anoxic conditions was markedly increased when the organisms were deprived of proline or were treated with chloramphenicol for the initial period after irradiation. Either treatment was equally effective and the maximum degree of survival which was obtained was above that observed when the cells had been incubated throughout on a proline + inorganic salts + glucose medium. The depression in survival caused by including NaCl in the defined nutrient medium, on which the irradiated bacteria were grown, was completely eliminated by both treatments. ‘Rescue’ appears to depend on the temporary inhibition of protein synthesis.

Summary: The germination of spores of Clostridium bifermentans in media based on acid hydrolysates of casein has been studied. Germination of spores was estimated by observing the decrease in turbidity of a spore suspension and confirmed by observation with the phase contrast microscope and by the increase in permeability to stains. The optimum conditions for germination of spores suspended in phosphate buffer were incubation at 37° within the range pH 6·0-7·8 following heat shock at 85° for 10 min. Anaerobic conditions were not necessary for germination, and addition of mercaptoacetate decreased the rate of germination. The minimum requirements of compounds needed for the germination of spores of C. bifermentans was the presence of L-α-alanine, L-phenylalanine and lactate. L-phenylalanine could be replaced by L-leucine but the rate of germination was slower. L-α-Alanine was essential for germination and was not replaced by any other amino acid examined.

Summary: Ten leucine-requiring mutants of Salmonella typhimurium were induced to revert with the alkylating agent, diethylsulphate (DES). The pattern of reversion was studied by following the appearance of leucine-independent colonies on minimal plates, and of turbid (revertant) tubes among tubes containing 105-106 treated bacteria in minimal medium. Five mutants gave high (0·6-5 x 10−5) frequencies of reversion. The other five gave lower (5 x 10−8-1·3 x 10−6) frequencies immediately after plating on minimal agar or dilution in minimal medium, but reversion continued to take place until a high frequency was attained. This delayed mutation was found to be independent of cell metabolism. The possibility is discussed that the different patterns of reversion reflect alkylation of different base pairs. It is suggested that mutants having guanine: cytosine (G:C) base pairs at the mutant site revert mainly by pairing errors made by alkylated guanine. Mutants with adenine: thymine (A:T) sites are assumed to revert through the production of apurinic gaps, formed by the hydrolysis of ethyladenine.

Summary: When synchronized single-generation cultures of the unicellular water mould Blastocladiella britannica are grown in the presence of white light, they develop into nearly colourless thin-walled sporangia; in the dark they develop into brown pitted thick-walled resistant sporangia. Under these conditions, dry weight/cell increases exponentially at the same rate in light and dark. However, the capacity for uptake of glucose by cells of various ages grown in the dark exceeds that of light-grown cells. Furthermore, just as the course of development along either of the two morphogenetic pathways can be reversed by excluding or supplying light before their respective points of no return, so, too, the rise in their capacities for glucose uptake can be similarly reversed. However, the point of no return for glucose uptake precedes the point of no return for morphogenesis by several hours. The light-sensitive glucose uptake by B. britannica may be a factor in determining the ultimate morphology of this organism.

Summary: High-frequency sonic oscillations destroyed the plaque-forming ability of actinophages. Among the 31 actinophage strains studied, the fraction of viral particles which survived an exposure for 1 min. to vibrations of 20 kcyc./sec. varied from 100 to 0·0002%. Coliphage T2hr+ was more susceptible to ultrasonic treatment than were some actinophages and was more resistant than other actinophages. In general, large actinophage particles were more sensitive to sonic treatment than small particles. A 60 W. 20 kcyc./sec. M.S.E. Ultrasonic Disintegrator destroyed actinophages more rapidly than a 50 W., 9 kcyc./sec. Raytheon Sonic Oscillator. Electron micrographs of actinophage MSP8 treated with sonic vibrations showed progressive disruption of the viral particles. Susceptibility to sonic inactivation gave an additional criterion for grouping actinophages.

Summary: Strains of three groups of Mycoplasma with different nutritional requirements were analysed for β-glucosidase activity. The enzyme was found in the cell membrane of Mycoplasma laidlawii strain b and M. gallisepticum strain J, which metabolize carbohydrates; negligible β-glucosidase activity was found in M. hominis strain 07 which does not metabolize carbohydrates. βglucosidase in all strains was inactivated by heating at 56° for 30 min. or at 100° for 10 min. With M. laidlawii strain B as the test organism, βglucosidase was found to possess the following characteristics: pH optimum, 6·8; optimum temperature, 30°; no dialysable cofactors required; phosphate ions had no effect on activity; enzyme was specific for substrates (glucosides) with β configuration; aglycon of the glucoside must be an aryl group; enzyme exhibited absolute specificity for carbon atoms number 4 and 5 of the glycon. The presence of β-glucosidase in M. laidlawii strain B and M. gallisepticum strain J is assumed to be involved in the synthesis and hydrolysis of carotenyl glucoside and sterol glucoside by these organisms.

Summary: Sodium azide, 2,4-dinitrophenol and iodoacetate did not inhibit hydrolysis of lactose by cell-free preparations of Saccharomyces fragilis β-galactosidase, but with intact organisms fermentation and hydrolysis were inhibited to a similar extent. This suggests that these inhibitors may interfere with the transport of lactose into the cell. Galactose fermentation was inhibited by sodium azide and dinitrophenol to a much greater extent than was glucose or lactose fermentation. Hydrolysis of lactose and o-nitrophenyl-β-d-galactoside required potassium ion at an optimal concentration of 0·1M; ammonium ion also activated, but sodium ion was much less effective and, in presence of optimal concentrations of potassium ion, were inhibitory, as were calcium and zinc ions. Lithium, magnesium and manganese ions were without effect in presence of potassium optimal ion. The β-galactosidase activity of aqueous suspensions of acetone-dried organisms, or of cell-free extracts, decayed rapidly at 25°. This decay was prevented by addition of sodium phosphate or various potassium salts, but not by sodium or potassium chloride or by potassium sulphate. Sodium azide, arsenate or 2,4-dinitrophenol decreased the rate of decay and promoted partial recovery when decayed preparations were subsequently incubated with potassium phosphate. The enzyme was most stable in 0·1m-potassium phosphate (pH 7·0). A purified (237-fold) preparation of the β-galactosidase was obtained; this too decayed rapidly in water or potassium chloride solution but not in potassium phosphate solution.

Summary: The decay of β-galactosidase activity which occurs when acetone-dried Saccharomyces fragilis organisms are suspended in water at 25° is prevented by various potassium salts, sodium sulphide, azide, fluoride and citrate, manganous chloride and sulphate, cobaltous chloride, oxine, diethyldithio-carbamate, dimethylglyoxime and 2,4-dinitrophenol. Ethylenediamine-tetra-acetate (EDTA) has no effect on the decay but inhibits the enzyme, the inhibition being annulled by various metal cations, notably manganous and ferrous ions. Sodium pyrophosphate increased β-galactosidase activity of intact organisms. This effect is to some extent reversible and is prevented by glucose. It is not accompanied by uptake of sodium pyrophosphate into the organisms. The possible mode of action of pyrophosphate is discussed.

Summary: Forty-five strains of sulphate-reducing bacteria showed marked differences in their resistance to Hibitane (I.C.I. Ltd.) and, to a lesser degree, to cetyltrimethylammonium bromide. Panacide (British Drug Houses Ltd.) was effective against all the strains. The relevance of these findings to modern views on the taxonomy of the sulphate-reducers and to the problem of inhibiting these organisms in the field is discussed.

Summary: All of eight Mycoplasma strains tested were capable of hydrolysing tributyrin. The saprophytic Mycoplasma laidlawii strains showed the lowest lipolytic activity, and the parasitic Mycoplasma gallisepticum the highest. The properties of M. gallisepticum lipase were studied in some detail. The lipolytic activity of this organism was highest at the logarithmic phase of growth and declined steeply afterwards. The enzyme was not bound to the cell membrane and appeared in the soluble fraction of disrupted cells. The cell extract hydrolysed tributyrin much faster than trilaurin or triolein. Methyl oleate and ‘Tween 80’ were only slowly hydrolysed. Cholesteryl acetate and stearate were not hydrolysed by cell extract or by intact M. gallisepticum. Partial purification of the lipase was accomplished by ammonium sulphate fractionation of cell-extract proteins, followed by anion-exchange chromatography. The partially purified enzyme did not require inorganic ions for activity and its optimal pH value varied between 7·5 and 8·0, depending on the substrate tested.

Summary: Salmonella typhimurium Q1, when grown in standard medium at a temperature of 37°, is a uninuclear organism in which nuclear division precedes cell division, so that some 25 to 30% of the bacteria show various stages of nuclear division. When incubated at a lower temperature (e.g. 25°) nuclear division outruns cell division, and binucleate and quadrinucleate forms appear. In experiments at 37°, infection of Q1 or superinfection of Q1 (A1 a) with temperate phage A1 b temporarily arrests bacterial division, producing a lag period of 30–45 min. Decision to lyse is taken from 1 to 9 min. after exposure to infection, and the ensuing productive development leading to the release of a brood of temperate phage particles is an immediate sequel of this decision. Decision to lysogenize, as evidenced by immunity to a heavy challenge by homologous virulent phage, is taken within one minute of infection. 60 to 70% of bacteria infected or super-infected with a single phage particle produce pure clones of lysogenized, prophage-substituted, or doubly lysogenized bacteria. It is suggested that the mixed clones of uninfected and converted bacteria derived from the remaining 30 to 40% may result from the lysogenization of one-half of a nucleus already embarked on the process of division; evidence favouring this theory is discussed. It is concluded that, contrary to current belief, and under the conditions of our experiments, the infective material of a phage particle which has penetrated a sensitive bacterium proceeds with little delay either to become integrated with the chromosome as prophage or to undergo productive development and produce lysis, and does not remain for one or more bacterial generations an unattached cytoplasmic inclusion.

Summary: The corrected sedimentation coefficients, expressed as (S 20,w)0, of ribosomes from nine different yeasts, representing a wide taxonomic range, were found to be 51·5 ± 2·4, 68·6 ± 3·3 and 86·7 ± 2·9 x 10−13 sec. Very small quantities of a faster (approximately 128 x 10−13 sec.) and a slower particle were sometimes detected. Yeast ribosomes have thus sedimentation coefficients which are distinctly different from bacterial ribosomes.