- Volume 46, Issue 3, 1967

Host cell reactivation (hcr) of phage T1 by two strains of Escherichia coli k 12, Hfr c (λ +)thy – and Hfr b 1 (λ –)thy –, was studied. Strain Hfr c showed decreased ability to reactivate ultraviolet (u.v.)-irradiated phage T1, as predicted from its behaviour in mating experiments after thymine starvation. Thymine starvation of host Hfr B 1 bacteria resembled u.v. irradiation in decreasing hcr, but thymine starvation of Hfrc increased hcr, apparently as a result of λ induction. The presence of λ prophage in E. coli k 12 was found to decrease hcr.

The exposure of tryptophan-requiring Escherichia coli b/r wp2 to u.v.- and γ-irradiation (in either order) results in more revertants than would be expected if the two treatments were independent. The excess mutants (‘interaction mutants’) were produced in increasing number by increasing doses of u. v.-or γ-radiation. Evidence is presented that the interaction occurs post-irradiation. Although the excision-repair and mutation frequency decline systems for u.v. damage are not involved in the interaction itself (since a strain deficient in these systems, E. coli wp2 her–, is no less efficient at producing interaction mutants than E. coli b/r wp 2) the u.v. component involved in interaction is sensitive to one or both of these systems as is shown by the very much lower u.v. doses at which interaction occurs in E. coli wp2 her–.

The effect of various modifying agents has been studied on the synergistic interaction of u.v.- and γ-radiation in the induction of prototrophic revertants of tryptophan-requiring Escherichia coli b/r wp2. The component of γ-radiation damage involved in the interaction shows a large effect of oxygen during irradiation (dose modifying factor of up to 3) and is thus more like lethal than mutational damage. The interaction mutants respond to various post-irradiation treatments in the same way as u.v.-induced, but not γ-induced, mutants, i.e. they are photoreactivable, their frequency is increased by acri-flavine and nutrient broth after irradiation and they are susceptible to mutation frequency decline in minimal medium. It is postulated that damage induced in DNA by γ-radiation inhibits the repair of premutational lesions induced by u.v. thus increasing the yield of u.v.-induced mutants. The possible nature of the system involved in this repair (which is not that responsible for the excision of thymine dimers from DNA) is discussed.

Exogenous citrate induced the growing thin-walled ordinary colourless form (OC cell) of the water fungus Blastocladiella emersonii to produce more citric acid and, simultaneously, to re-utilize lactic acid liberated previously in one large wave of activity. In the absence of added citrate, release of citric acid was not detectable at the end of the cell’s generation time, while production and re-utilization of lactic acid did occur, but in very small amounts and in a series of successive waves. An increase in the generation time of an OC cell, previously known to be induced by visible light, was also induced by exogenous citrate in the dark, provided environmental conditions were favourable. Furthermore, increasing amounts of exogenous CO2 increasingly decreased the dark generation time; this inhibition was annulled by light. Some effects of gaseous (CO2/O2) and ionic (Na+/K+) balance are also described.

One hundred and forty-eight Gram-negative bacteria, mostly pseudo-monads and achromobacters, were tested for glucose utilization by detection of acid production and by an enzymic method for detecting residual glucose. The enzyme test showed that some bacteria which produced little or no acid in glucose media (e.g. Pseudomonas maltophilia, Pseudomonas groups III and IV of Shewan, Hobbs & Hodgkiss, 1960) did remove glucose from the media. Representatives of the genus Comamonas did not produce acid from glucose or remove it.

Three distinct species of the genus Nitzschia, lacking chloroplasts and therefore obligately heterotrophic, were isolated in pure culture from various marine shores. The organisms reproduced rapidly in a defined medium based on an artificial sea water supplemented with mineral nutrients, thiamine and cobalamin. Lactate or succinate served as sole organic carbon source for all three species; two of the species also used glucose or glutamate. Two of the species were identified as N. putrida Benecke and N. leucosigma Benecke, respectively. The third organism appears to be a new species, here named N. alba.

The present report gives the results of studies on the % guanine+cytosine (GC) content of the DNA of 29 strains designated as Micrococcus, by using the methods of Marmur & Doty (1962) and Frédéricq, Oth&Fontaine (1961). In 17 strains agreement was found between their taxonomic position and their % GC content. Five micrococci formed a very tight cluster around a mean of 50% GC. It is recommended to classify them in the genus Planococcus Migula. From the DNA base compositions these cocci form a group hitherto not described, intermediate between the genera Staphylococcus and Micrococcus. Micrococcus cryophilus McLean, Sulzbacher&Mudd, and Micrococcus cerolyticus Friedman&Kern differ in their % GC values from those of the genus Micrococcus and should be discarded from the genus. It is confirmed that % GC content in the DNA in the genus Micrococcus lies within the range of 65–75%.

Tetrin A, a polyene antifungal antibiotic, induced permeability changes in the cell membrane of Saccharomyces cerevisiae, resulting in the loss of cell constituents, e.g. amino acids, 260 mμ absorbing material and the leakage of labelled metabolites from the organism previously grown with uniformly labelled glucose. Also, the uptake of glucose, glycine, and uracil was prevented by the antibiotic. Like other polyenes, the addition of exogenous cholesterol partially prevented the action of tetrin A, probably by the formation of a weak complex between tetrin A and cholesterol and resulting in a lower effective concentration of the antibiotic. When the non-sterol-containing fungus Pythium ultimum was grown on a medium containing cholesterol, this fungus was sensitive to filipin. However, prior growth of the fungus with cholesterol did not confer sensitivity to the polyene antibiotics tetrin A, nystatin, or pimaricin. Contrary to most polyene antibiotics which cause rapid lysis of mammalian erythrocytes even at low concentrations, tetrin A only caused partial lysis of calf red cells after long exposure to high concentrations.

Two types of mutants of Aerobacter aerogenes were obtained which grow anaerobically in a minimal medium with glucose as sole carbon source, but which require either succinate or methionine + lysine for aerobic growth in this medium. Only one type of mutant grew in minimal medium with succinate as sole carbon source. This type accumulated pyruvate and α-oxoglutarate during growth in minimal medium with glucose and succinate. It is apparently blocked in the oxidation of α-oxoacids. The other type of mutants accumulated only α-oxoglutarate during growth in minimal medium with glucose and succinate. Cell-free extracts of this type of mutant did not contain α-oxoglutarate dehydrogenase and washed organisms were unable to oxidize acetate. The aerobic molar growth yield of the mutant in minimal medium with glucose, methionine and lysine was much smaller than that of the wild type. Anaerobic growth of these mutants was strongly inhibited by nitrate; this inhibition was prevented by the addition of succinate.

The production of urease by Acinetobacter lwoffii and A. anitratus was studied in 20 strains. It is concluded that both species may produce urease under appropriate conditions and that this property is of no value in differentiating between them. This conclusion was tested in 40 other strains of which 37 produced urease independently of saccharolytic activity.

Two methods are described for determining the shortest route to an identification. The methods are based upon the reduction to a minimum test set, as suggested by Gyllenberg (1963), which will result in the most efficient separation of the organisms. The first method is used when no test results for characters are considered variable; the second method is applicable when some characters are variable and others are not. To illustrate the methods two sets of data are reduced. One set includes the reduction to a minimum set of 6 tests from 32 tests for 36 organisms in the Enterobac-teriaceae. The other set includes the reduction to a minimum set of 3 tests from 34 tests for 8 Pasteurella species. The methods described may be used manually or be programmed for a computer.

Cultures of 10 of 19 nomenspecies of the genus Xanthomonas liquefied a nutrient pectate gel. None of the 19 nomenspecies produced either hydrolytic polygalacturonase or pectin trans-eliminase. Seventeen of the nomenspecies showed a detectable, at times weak, pectinesterase activity. Seven of the 10 pectate-liquefying nomenspecies excreted polygalacturonic acid trans-eliminase in culture fluids containing pectin as growth substrate. The enzymo-logical basis, if any, is not at present known for the liquefaction of the nutrient pectate gel in the remaining three xanthomonads, which all lacked both the hydrolytic and the eliminative enzymes. Pectinesterase and polygalacturonic acid trans-eliminase were produced inducibly on pectin by most X. campestris cultures which were examined; some strains of this phytopathogen formed polygalacturonic acid trans-eliminase constitutively on glucose, but pectinesterase was never constitutive. The polygalacturonic acid trans-eliminase excreted by the tested xanthomonads degraded polygalacturonic acid in a random manner. The major end-products were unsaturated di- and tri-galacturonic acids, accompanied by lesser amounts of saturated mono-, di-, and tri-galacturonic acids.

Growth of lymphogranuloma venereum (LGV) agent in HeLa cells has been studied by light and electron microscopy. Infective elementary bodies enter the host cell by phagocytosis, transform directly into the larger forms known as initial bodies, and multiply by fission within a vesicular cytoplasmic inclusion. Later in the growth cycle, elementary bodies are produced by a process involving internal condensation and a progressive reduction in size of the dividing initial bodies. An envelope with two layers, ribosome-like granules and filamentous ‘nuclear’ material are components common to all developmental forms of the LGV agent. Penicillin prevents multiplication of initial bodies, but not their growth; the very large and vacuolated penicillin forms are similar to bacterial spheroplasts. 5-Fluorouracil affects chiefly the later part of the LGV growth cycle; non-infective forms develop, and the maturation of elementary bodies is blocked. The findings endorse the view that the psittacosis–lymphogranuloma–trachoma group agents are not viruses, but have close affinities with rickettsiae and certain bacteria.

Bovine actinomycosis exudate was studied to determine the chemical composition and mineral phase(s) of the so-called ‘sulphur granules’. The major constituents, CaO and P2Os, accounted for 86–89% of the ashed granules. The granules also contained Na, K, Mg (as oxides) and Cl which added up to 10–14 %. Although the X-ray diffraction patterns indicated only poorly formed apatite; the infrared spectrum could be interpreted as arising from poorly crystallized apatite and/or a partially dehydrated or hydrolysed octacalcium phosphate either or both mixed with anhydrous dicalcium phosphate. The formation of pyrophosphate (44·5 %) in the ignited granules indicated the presence of considerable acid phosphate in the original material.

The behaviour of certain non-nitrogenous compounds in mycelium of Aspergillus terreus during autolysis in culture medium was studied. The mycelium of A. terreus lost during autolysis 45 % of its maximum dry weight. The amount of glucose, which was present from the beginning of autolysis throughout the whole further period of incubation, continuously increased to a maximum and then sharply descended to a constant value. Xylose decreased to half of its initial concentration during the first 30 days of autolysis and then disappeared. Mannitol descended in 95 % between the 18th and the 114th day of autolysis. Seventy-four % of the fat present at the beginning of autolysis was lost during the first 138 days of autolysis. The disappearance of fat and mannitol accounted for about 48 % of the dry wt. of mycelium lost during the whole period of autolysis.