- Volume 27, Issue 3, 1962

SUMMARY: Heterokaryons obtained between nutritional mutants of the imperfect fungus Verticillium albo-atrum (Reinke & Berth) were very unstable, and heterokaryotic hyphal tips growing out from mixed inocula were difficult to find. Heterokaryotic conidia were not detected, in spite of the fact that about 1% of the spores contained two or three nuclei. Heterozygous nuclei in uninucleate conidia from mixed cultures yielded recombinant pheno-types at a higher frequency than usually observed in the other imperfect fungi which have been studied genetically. With no easily applicable criterion of chromosome number, such as spore size, the interpretation of results is difficult, but the genetic recombination demonstrated here seems likely to be accomplished through a parasexual system. Nuclei heterozygous at some loci but homozygous at others were formed from nuclei heterozygous at four marked loci, and were detected by isolating second-order segregants. These heterozygous segregants were presumably produced by mitotic recombination.

SUMMARY: Morphological, cultural and serological evidence is presented to suggest that a relationship exists between corynebacteria of human vaginal origin and pleuropneumonia-like organisms (PPLO). It is concluded that many PPLO are L-forms of corynebacteria, and that the differences between these and the L-forms of Gram-negative bacteria, most commonly studied, are in conformity with the differences between the parent bacterial forms.

SUMMARY: Electron microscopy of ultrathin sections enabled the fine structural peculiarities of a myxobacterium (Sorangium sp.) to be studied. The myxobacteria did not show the dense membrane characteristic of eubacterial cells. A very thin membrane in the myxobacteria cells was not distinguishable from the cytoplasm. In ultrathin sections of the myxobacteria there was observed a broad dark coloured cytoplasmic layer, a light mesh-like nuclear vacuole located in the centre of the cell and a rather large nucleus situated in the vacuole; the nucleus displayed density, dark colour and roundness. The elongated myxobacteria cells may include two to three nuclei. Phase-contrast microscopy of living unstained organisms of the Sorangium sp. studied revealed large rounded nuclei. The observations of living cells permitted the amitotic division of nuclei which precedes cell division in myxobacteria to be studied. The studies of the ultrathin sections with the aid of electron microscopy and the microscopy of the living cells supply similar data about the fine structure of the myxobacterial cells. The structure of the myxobacterial cells is more complicated than in the Eubacteria. The peculiar life cycle and the existence of a large nucleus easily detectable (by various methods) enables one to place the myxobacteria among the relatively highly organized micro-organisms.

SUMMARY: The ability of extracts of rabies-infected suckling mouse brains, freed from virus by centrifugation, to fix complement in the presence of mouse anti-rabies serum was confirmed. The complement-fixing (CF) activity, which was unstable, was partially purified by precipitation, solvent treatment, adsorption, chromatography and electrophoresis. There appeared to be constituents of normal brain which closely resembled the CF activity in their behaviour towards these treatments. Descriptions are given: of (a) a device for stepwise elution of chromatograph columns; (b) modifications to the LKB Produkter electrophoresis apparatus to ensure constant electrical resistance; (c) a method for estimating ‘protein’ which is useful when the ultra-violet (u.v.) radiation method is inapplicable.

SUMMARY: Virus-free extracts of rabies-infected suckling mouse brains contain a relatively large antigen which is slowly sedimentable at 70,000 g and resistant to trypsin; a smaller antigen which is destroyed by trypsin; probably at least two antigens of intermediate size also probably sensitive to trypsin. The antigens differ but slightly from each other and from one or more brain components in electrophoretic mobility in agar and in chromatographic behaviour on DEAE cellulose.

SUMMARY: Two further groups of pigment mutants have been isolated from irradiated suspensions of the non-sulphur purple bacterium Rhodopseudomonas spheroides. Both contain the normal red carotenoid of the wild type, but in place of bacteriochlorophyll one group contains a derivative at the oxidation level of chlorophyll a, and the other a pigment at the oxidation level of protochlorophyll. Both these groups are non-photosynthetic. All attempts to produce stable photosynthetic mutants containing a pigment absorbing at the same wavelengths as chlorophyll a failed, although transient photosynthesis seemed to occur on several occasions. The relationship of these mutants to the biosynthetic pathway of bacteriochlorophyll suggested by Granick is discussed.

SUMMARY: The cellular form of Trigonopsis variabilis may be either triangular or ellipsoidal in outline. Development of form in this yeast is subject to nutritional control. Cell populations, almost exclusively of triangular form, are obtained in defined media containing methionine, or other suitable methyl group donor. Cultures in defined media devoid of methyl group donor usually consist exclusively of ellipsoidal forms.

SUMMARY: Extraction and fractionation of lipids from intact ellipsoidal and triangular forms of Trigonopsis variabilis showed both to be rich in lipid, the content in triangular forms being twice that in ellipsoidal forms. Lipid was chiefly present in bound form with which principally choline was associated in triangular cells, whilst in ellipsoidal cells ethanolamine and serine predominated. Very little unsaturated lipid was found in the triangular forms, whereas a threefold greater iodine value was noted with the ellipsoidal forms. Polysaccharides of both cellular forms were extracted and fractionated. The triangular forms were seemingly devoid of glucan or chitin but contained a reducing polysaccharide that formed an unusual copper complex and appeared to be a polymer of glucose and mannose. The ellipsoidal forms contained a small amount of glucan and considerable amounts of glycogen. Cell walls were isolated from both triangular and ellipsoidal forms and found to consist principally of polysaccharide, nearly all of which was alkali-soluble. Walls of triangular forms contained somewhat more lipid than those of ellipsoidal forms, and phospholipid was twice that of ellipsoidal form walls.

SUMMARY: The yeast Trigonopsis variabilis can utilize many single amino acids as sole source of nitrogen. Of the amino acids utilized, the d-isomers are oxidatively deaminated, whilst the l-isomers are transaminated with either α-ketoglutarate or pyruvate. The d-amino acid oxidase activity of this organism, when grown on dl-methionine as sole source of nitrogen, is the highest yet recorded, and may be recommended for the preparation of keto acids.

SUMMARY: Mutants of a strain of Rhizobium trifolii were obtained by selective action of bacteriophage and streptomycin and by exposure to ultraviolet (u.v.) radiation. All mutants resistant to bacteriophage were streptomycin-susceptible and all resistant to streptomycin were bacteriophage-susceptible; no survivor after exposure to u.v. radiation resisted either the bacteriophage or streptomycin. Mutation to bacteriophage resistance was closely correlated with inability to fix nitrogen in symbiosis with red clover. Some streptomycin-resistant mutants used streptomycin as a nutrient supplement, enabling them to grow on a mineral medium without growth factors. All but two mutants remained serologically indistinguishable from the original strain.

SUMMARY: The Rothamsted culture of tobacco necrosis virus contains two serologically unrelated viruses one of which, called the ‘satellite virus’ (SV), causes no lesions and multiplies detectably only when the other (TNV) is present. It decreases the size of necrotic local lesions formed by TNV. Inocula containing both viruses gave the same, fewer or more lesions than inocula containing only TNV; the results depended on the ratio of the two viruses in the mixed inoculum, on the species and age of the test plants and, particularly, on the temperature at which the plants were kept after the inoculation. The concentration of TNV decreased when SV was also present; the extent of the decrease depended on the ratio of the two viruses in the inoculum and other factors. Inoculation with SV 5 days before inoculation with TNV still decreased lesion size and led to the multiplication of SV. Phenol-disrupted SV affected lesion size only when inoculation with TNV followed within a few hours, but when inoculation with TNV was delayed by up to 2 days, SV sometimes multiplied detectably. SV has the smallest particle reported for any plant virus; diameter c. 17 mμ and weight equivalent to a molecular weight of about 1·9 x 106, of which 20% is nucleic acid. It is exceptionally stable, retaining infectivity after 17 years at 3° and after heating for 10 min. at 90°. TNV was much more susceptible to inactivation by heat and by ultraviolet light than SV. The two differed greatly in electrophoretic mobility and were readily separated from mixed preparations by electrophoresis.

SUMMARY: Rod-shaped particles suspended in a liquid undergo a partial orientation during flow; the flowing suspension has the property of scattering light mainly in certain preferred directions. The elementary theory of the phenomenon shows that it can be applied practically as a photometric method of following changes in length. A simple and effective apparatus for this purpose is described, and its performance illustrated. A brief discussion of size changes in synchronized cultures indicates the relation between these changes and the rate of fission.

SUMMARY: The viruses of trachoma and inclusion blennorrhoea, like other members of the psittacosis-lymphogranuloma group, contain heat-stable and heat-labile complement-fixing antigens. The heat-stable antigen, which is soluble in ether and partly destroyed by periodate, appears to be chemically similar, as well as serologically related to, the lipopolysaccharide-protein complex shared by other viruses of the group. Complement-fixing group antigen was detected at all times during one cycle of multiplication of a strain of inclusion blennorrohea virus in HeLa cells. The amount of cell-associated antigen, about half of which sedimented under the same conditions as mature elementary bodies, remained constant for the first 16 hr. after adsorption; after 16 hr. it increased linearly, reaching a maximum 28 hr. after adsorption. The group antigen probably forms at a stage in the developmental cycle when large forms predominate and is later distributed among the smaller infectious elementary bodies.

SUMMARY: The establishment of vesicular-arbuscular mycorrhizal infections by inoculation with germinated resting spores of an Endogone sp. was investigated under microbiologically controlled conditions; pure two-membered cultures were obtained for the first time.

Seedlings were grown in a nitrogen-deficient inorganic salt medium; in these conditions the fungus failed to form an appressorium and to penetrate the plant roots unless a Pseudomonas sp. was also added. Adding soluble nitrogen to the medium completely inhibited root penetration, even in the presence of the bacteria. Various sterile filtrates could be used to replace the bacterial inoculum but these substitutes induced only few infections per plant.

Mycorrhizal roots grew more vigorously than non-mycorrhizal roots of the same seedling. They were longer and more profusely branched. At first mycorrhizal infections were predominantly arbuscular, but many prominent vesicles developed as the seedlings declined, and then the fungus grew out of infected roots and colonized the agar. The fungus could not be subcultured without a living host.

The possible interpretation of these results is considered with reference to the specialized nutritional conditions under which test plants were grown.

SUMMARY: Resting organisms of Shigella flexneri 3 were able to synthesize protein and nucleic acids in a chemically defined medium. Protein synthesis was markedly inhibited while ribonucleic acid (RNA) synthesis was stimulated by low concentrations of chloramphenicol; deoxyribonucleic acid synthesis was inhibited slightly. Neither glycine, l-phenylalanine nor l-tyrosine annulled the action of the antibiotic. Inhibition of protein synthesis and stimulation of RNA synthesis in resting organisms of a chloramphenicol-resistant mutant of S. flexneri 3 was observed only in the presence of high concentrations of chloramphenicol. The results presented in this paper show that chloramphenicol suppresses the growth of S. flexneri 3 by interfering with the synthesis of protein. The stimulation of RNA synthesis suggests that chloramphenicol may exert its inhibitory action by promoting the formation of RNA with altered biological activity.