Inactivation of Thirty Viruses by Gamma Radiation

Decimal reduction values (D value) for 30 viruses were determined. The weighted D values of the viruses suspended in Eagle's minimum essential medium ranged from 0.39 to 0.53 Mrads. It was necessary to increase the radiation dose by a factor of >3 to inactivate virus suspended in Eagle's minimum essential medium as compared to the same virus suspended in distilled water. The destruction rate curves were of a first-order reaction.     

Metabolic Regulation by Homoserine in Escherichia coli B/r

A mathematical analysis of branched pathway regulation has led to the prediction of a novel homoserine control in Escherichia coli B. Experimental support for such control is presented in this paper. Homoserine, the precursor of both threonine and methionine, inhibits nicotinamide adenine dinucleotide phosphate (NADP(+))-specific glutamate dehydrogenase (EC 1.4.1.4), the enzyme catalyzing the first reaction in ammonia assimilation. Physiological and biochemical evidence for this effect are offered. Homoserine depresses the growth rate of the organism, and glutamate, the product of the inhibited reaction, reverses this effect. The NADP(+)-specific glutamate dehydrogenase activity in cell-free extracts is inhibited by homoserine, and this inhibition parallels the restriction of growth rate. These effects are found in other enteric bacteria which share a similar overall pattern of control for the amino acids derived from aspartate. On the other hand, a sampling of more distantly related species which have different pathways and/or regulatory patterns provides no evidence for homoserine inhibition of the glutamate dehydrogenase reaction.     

Role of Differential Air Pressure Zones in the Control of Aerosols in a Large Animal Isolation Facility

The uncontrolled transmission of hog cholera in a large animal isolation facility, designed to control the movement of aerosols within and between individual wings of a multiunit building, indicated the need for a critical study of aerosol behavior under existing conditions of operation. Studies with aerosols of Escherichia coli B T3 bacteriophage (T3 coliphage) conclusively demonstrated the impossibility of obtaining the desired control by means of a "static" air balance relationship between adjacent areas within the facility. Modifications needed to provide the desired control of the air-handling system are outlined and discussed.     

Adventitious shoot regeneration from leaf tissue of three pear (Pyrus sp.) cultivars in vitro

To develop an adventitious regeneration system for pear cultivars, several experiments were conducted with 2 cultivars of Pyrus communis L. (Seckel and Louise Bonne) and one cultivar of P. bretschneideri Rehd. (Crystal Pear). Half-leaves, taken from shoots proliferating on Lepoivre medium, were plated in petri-dishes on medium supplemented with various combinations of cytokinins and auxins. Cultures of the above cultivars had been established from mature trees. Among the growth regulators tested, thidiazuron (TDZ), combined with naphthalene-acetic acid (NAA), was the most efficient for stimulation of adventitious shoots. The optimum level of TDZ was about 3 uM; shoot regeneration was observed over a wide range of TDZ and NAA concentrations (0.5 to 5 uM and 2.5 to 13 um, respectively). Among different macronutrient compositions, 1/2 and 1/4 Murashige and Skoog were the most effective. Sucrose concentrations (10 to 50 g L-1) had a linear significant effect on shoot regeneration of Crystal Pear.Abbreviations BAP 6-benzylaminopurine - IBA indole-3-butyric acid - NAA a-naphthaleneacetic acid - NoA 2-naphthoxyacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - TDZ thidiazuron (N-phenyl-N'-1,2,3-thidiazol-5-ylurea) - MS Murashige and Skoog (1962) macroelements - L Lepoivre (Quoirin and Lepoivre, 1977) macroelements     

Temperature dependence of inorganic nitrogen uptake and assimilation in Antarctic sea-ice microalgae

Summary The influence of temperature on NO ₃ ^- and NH ₄ ⁺ uptake, and the activity of the assimilatory enzyme NO ₃ ^- reductase (NR) was compared to inorganic C uptake (photosynthesis) in natural assemblages of Antarctic sea-ice microalgae. NO ₃ ^- and NH ₄ ⁺ uptake reached a maximum between 0.5°–2.0°C and 2.0°–3.0°C, respectively, which was close to that for photosynthesis (2.5°–3.0°C). NR showed a distinctly higher temperature maximum (10.0°–12.0°C) and a lower Q₁₀ value than inorganic N and C transport. Our data imply that, owing to differential temperature characteristics between N transport and N assimilation at in situ temperature (-1.9°C), the incorporation of extracellular NO ₃ ^- into cellular macromolecules, may be limited by transport of NO ₃ ^- into the cell rather than the intracellular reduction of NO ₃ ^- to NH ₄ ⁺ . Despite differences in temperature maxima between N transport and N assimilation, the overall low temperature maxima of inorganic N metabolism characterizes Antarctic sea-ice microalgae as psychrophilic. Our study is the first to examine the temperature dependence of inorganic N uptake and assimilation in sea-ice microbial communities.     

Linkage analysis of seven kindreds with the X-linked lymphoproliferative syndrome (XLP) confirms that the XLP locus is near DXS42 and DXS37

Summary Analysis of seven kindreds indicates that the XLP locus exhibits 1% recombination with DXS42 (lod = 17.5) and no recombination with DXS37 (lod = 13.3).