- Volume 38, Issue 3, 1965

Several phosphatases have been demonstrated in Dictyostelium discoideum. The alkaline phosphatase, pH optimum 9·0, is a 5′-nucleotidase, attacking adenosine monophosphate and deoxyadenosine monophosphate, but catalyses also hydrolysis of p-nitrophenyl phosphate. In the absence of exogenous nutrients this enzyme increases about 6-fold in vitro during differentiation. Its activity in vivo may in part be controlled through endproduct inhibition by orthophosphate which has been found to accumulate in the cells during sporulation. Exogenous orthophosphate and glucose repress the levels of alkaline phosphatase in the spores. The data support the conclusion that end product inhibition and repression collaborate to ensure maximal alkaline phosphatase activity in vivo during culmination. Exogenous adenosine and deoxyadenosine increase the alkaline phosphatase levels in the sorocarps.

The diversity of colonial types of Pseudomonas aeruginosa which may be encountered is described, together with a series of biochemical tests and the application of serological and pyocine typing which are of use in identifying atypical strains. These methods are particularly recommended for strains which do not form pigment. It is suggested that absence of pigment production even on special media does not preclude the possibility that a strain is P. aeruginosa.

The presence of inorganic or organic iron in the growth medium induces the production of a reddish-violet pigment in Micrococcus violagabriellae. This pigment protects the organism against short exposures to ultraviolet (u.v.) radiation of wavelength below 300 mμ. The presence of iron also increases the degree of recovery of the normally white organism after such irradiation. Anaerobic growth renders both the red and the white micrococci more resistant to damage by u.v. radiation. However, the addition of nitrate, an alternative to oxygen as a terminal electron acceptor, restores the u.v. sensitivity of these micrococci to that of aerobically grown organisms. It is suggested that the initial site of u.v. irradiation damage is extranuclear and involves one or more cytochrome-linked systems, and that it is within this system(s) that the iron functions both as a radiation-protective and as a restorative agent.

Plasma of rats infected with Trypanosoma evansi contained soluble antigen detected by the agar diffusion method. The antigen protected mice against homologous challenge but was not agglutinogenic. Whether the two properties were due to one or two antigens, respectively, was not ascertained. Trypanosome homogenate contained three antigens, two of which were exclusive to the trypanosome, whereas the third antigen was the same as the soluble antigen of the infected rat plasma as established by the gel diffusion and indirect haemagglutination tests.

A study has been made of 607 cultures of Gram-positive and catalase-positive cocci received from workers and collections in different parts of the world. These cultures were examined for a wide range of morphological and physiological characters and representative cultures were further studied to determine the chemical constituents of the organisms. Five hundred and sixty-four of the cultures received were aerobic members of the Micrococcaceae, and of these 96% were classified in the author's groups and subgroups; a further subgroup was, however, introduced to accommodate the not previously studied pink-pigmented micrococci. It appears that the Gram-positive and catalase-positive cocci are best separated into the genus Staphylococcus and the genus Micrococcus on the ability of members of Staphylococcus to grow and produce acid from glucose anaerobically; six subgroups of staphylococci were recognized and eight of micrococci. The relationship of named species, groups and subgroups to the author's classification was examined; several species and groups of micrococci had been incorrectly classified. Thus, M. denitrificans, M. halodenitri-ficans and M. radiodurans possess characters which suggest that they should be reclassified with the Gram-negative genera and that Abd-El-Malek and Gibson's group IIIB should be classified with the Gram-positive microbacteria.

A filterable ether-sensitive agent was isolated from a pool of ticks collected during September 1960 from cattle in the Thogoto forest near Nairobi, Kenya. The pool consisted of Boophilus decoloratus, Rhipicephalus appendiculatus, R. simus and R. evertsi. The agent is apparently antigenically unrelated to 75 known arboviruses and is considered to be a previously undescribed virus, which has been named Thogoto virus. High degrees of immunity were found in livestock in some areas of East Africa.

A major feature in the classical conception of the morphology of the T-even type coliphage is the shape of the head, believed to be a bipyramidal hexagonal prism. The present paper shows that this shape is not consistent with the appearance in electron micrographs, and an alternative model is proposed. The fine structure of the head is compared with that of polymerized head protein (polyhead) obtained from naturally-occurring lethal mutants. Certain hexagonal and star-shaped objects have been described in the literature as base-plates. Because of inconsistencies in their appearance, they have now been measured and studied. The results given here indicate that the star-shaped objects are disorganized base-plates and the hexagonal objects are collars. By using the rotation method for printing micrographs of collars it is found that they have a hollow subunit at each corner.

Two seed pools of rhinovirus were contaminated accidentally at different times with the same virus. This contamination was detected only in certain ‘spinner flask’ experiments under circumstances which suggested the possibility that a mechanism other than contamination was responsible for the appearance of this virus. Experiments were made to test some of these possible mechanisms, but the results strongly indicated a contamination. The circumstances under which this contamination probably occurred are discussed.

Ureases of Proteus vulgaris, P. mirabilis and P. rettgeri were found to be serologically indistinguishable, while that of P. morganii was distinct from the other three. This finding, together with recent observations on the phage susceptibilities and base ratios of the nucleic acids of these organisms, would seem to indicate that P. mirabilis and P. rettgeri are merely variants of P. vulgaris, while P. morganii is a distinct species.

Vaccinia virus forms plaques in monolayers of RK 13, HEp. 2 and HeLa cells grown in concentrations of 5-fluorodeoxyuridine (FUDR) higher than those previously claimed to inhibit completely the synthesis of vaccinia virus DNA in suspended tissue cultures. The limited virus synthesis observed is not due to a varying susceptibility of the cells to FUDR, nor to the selection of virus resistant to FUDR. Experiments suggest that virus synthesis is made possible by thymidine from the DNA of dead cells.

The multiplication of rabbitpox virus in HeLa (ERK) cells was inhibited by p-fluorophenylalanine (FPA) 400 μg./ml. When added early in the growth cycle, FPA prevented the formation of viral DNA. The FPA-sensitive process necessary for DNA synthesis began about 11/4 hr after infection. This was at least 1 hr before the first development of viral DNA, but coincided with the time of synthesis of the earliest viral antigens. On the basis of this and other evidence, it is suggested that some soluble viral antigens are enzymes concerned in the synthesis of viral DNA.