- Volume 16, Issue 3, 1957

Summary: The accumulation of pyruvate in cultures of Proteus vulgaris grown with limiting concentrations of nicotinic acid has been investigated. Nicotinic acid-deficient organisms remaining in contact with a lactate medium under conditions where pyruvate accumulation is occurring gradually become deficient in thiamine. The thiamine content of organisms at various stages of growth was estimated, and a relationship between thiamine content and length of lag phase found. Maximum rates of pyruvate oxidation were obtained in organisms which were not deficient in either nicotinic acid or thiamine. The possible metabolic significance of these findings is discussed.

Summary: The variations in Vibrio cholerae studied included changes from Ogawa to Inaba type, smooth→rough, and motile→non-motile. With a sloppy-agar technique it was possible to estimate the rate of formation of these variants (i.e. probable mutation rate 1 in 105 and 1 in 104, respectively). It was possible to show that the action of antiserum in promoting the change from Ogawa to Inaba was selective rather than mutagenic. With the other two variations studied no selective process had to be considered owing to their high spontaneous rate of appearance. It may be said that all three variations studied were due to spontaneous mutants in the parent cultures giving rise to these forms.

Summary: The infectivity curve of the virus of foot-and-mouth disease was studied in cultures of suspended trypsinized cattle-tongue epithelial cells. By this technique a known number of cells could be exposed to a known amount of virus. The pattern of multiplication was that adsorption of the virus by the cells occurred rapidly and, except with low concentrations of virus, was complete in 15–30 min. A latent period of about 2·5 hr. followed during which the virus was closely associated with the cells, was protected from the neutralizing action of antiserum, was not readily extractable but retained its infectivity. At the end of the latent period the infected cells became producers of virus at a rate estimated to be between 102 and 103 ID 50/15 min. At about 12 hr. the infectivity of the culture began to decline because of death of virus-producing cells and thermal inactivation of the virus.

SUMMARY: Corynebacterium pyogenes has been observed to give rise to mutants which are indistinguishable from Corynebacterium haemolyticum. C. pyogenes ferments lactose and xylose (Xyl +), elaborates a soluble haemolysin and/or a proteolytic enzyme (H+), and its cell walls contain glucose units in addition to certain other components. On horse blood agar C. pyogenes forms small colonies (s) surrounded by large zones of haemolysis. C. haemolyticum and the mutant derived from C. pyogenes ferment lactose but not xylose, produce no soluble haemolysin, and glucose cannot be detected in hydrolysates of their cell walls. The change in the basal structure of the cell wall is accompanied by a lack of immunochemical cross-reaction between the wild type and the mutant or C. haemolyticum. On horse blood agar both C. haemolyticum and the mutant produce relatively large colonies (L) surrounded by narrow bands of haemolysis. The possibility that a single mutation involving cell- wall structure may account for the apparent change from Xyl+H+ to Xyl−H− is discussed. It is suggested that neither C. pyogenes nor C. haemolyticum is a corynebacterium, and that taxonomically both organisms belong to the genus Streptococcus.

SUMMARY: Influenza virus filaments can be made visible in the ordinary microscope by various staining procedures; a technique involving potassium permanganate and Victoria blue is described.

SUMMARY:Ultraviolet irradiation of spores of three leaf-infecting fungi, Botrytis fabae, Uromyces fabae (causes of ‘chocolate spot’ and rust of broad beans, respectively) and Erysiphe graminis (cause of barley powdery mildew), decreased their pathogenicity, as assessed by counts of local lesions or pustules. The infectivity of B. fabae was lost more rapidly than the ability to form colonies on agar; with E. graminis infectivity was lost more rapidly than the ability to germinate. Ultraviolet radiation damage to spores of all three fungi was mitigated by exposure to daylight after irradiation. The extent of such photoreactivation of B. fabae was the same whether the spores were on the host plant or in vitro. Ultraviolet irradiation of leaves before inoculation decreased the number of pustules of E. graminis on barley, had no effect on the pustule number caused by U. fabae and increased the number of lesions caused by B. fabae on broad beans. Rubbing leaves with Celite before inoculation also increased the number of B. fabae lesions. Retaining u.v.- irradiated broad bean plants in daylight or darkness after inoculation with unirradiated spores of B. fabae did not significantly alter the lesion number. In contrast, more pustules of E. graminis developed on u.v.-irradiated barley leaves kept in daylight than in darkness.