Germanium toxicity in selected bacterial and yeast strains

Summary The toxicity of germanium dioxide (GeO₂) to 21 bacterial and 13 yeast strains was investigated in liquid broth medium to obtain information on strains tolerant to high (1 to 2 mg/ml) GeO₂ concentrations.Arthrobacter sp. NRC 32005,enterobacter aerogenes NRC 2926,Klebsiella aerogenes NCTC 418 andPseudomonas putida NRC 5019 were tolerant to 1 mg/ml GeO₂.Bacillus sp. RC607 was able to grow in the presence of 2 mg/ml GeO₂ at pH 10 in broth culture. The yeastsCandida guilliermondii, Candida shehatae andPachysolen tannophilus were the most sensitive to GeO₂ as evidenced by their diminished growth rates at a GeO₂ concentration as low as 0.1 mg/ml. None of the yeast strains tested exhibited growth in the presence of 1 mg/ml GeO₂. The high pH of the medium containing germanium may be partially responsible for the growth inhibition of the yeast cultures. Select bacterial cultures previously exposed to 1 mg/ml GeO₂ could tolerate and grow better at 2 mg/ml GeO₂, suggesting the existence of very efficient adaptive mechanisms. The pH of the medium could modulate GeO₂ tolerance and this effect was found to be strain-dependent.     

Large-scale mapping and chromosome jumping in the q27 region of the human X chromosome

We have used pulsed field gel electrophoresis for further physical mapping studies in the q27 region of the human X chromosome. We show that the DXS 102 locus and the F9 gene are separated by only 300 kb despite a genetic distance of 1.4 cM; this linkage orients our large-scale map and shows that the mcf.2 transforming sequence is telomeric to F9. A BssHII complete-digest jumping library was used to jump toward the DXS 105 locus; a 130-kb jump was achieved and the corresponding "linking clone" was obtained.     

Protein denaturation during heat shock and related stress. Escherichia coli beta-galactosidase and Photinus pyralis luciferase inactivation in mouse cells

In an attempt to question the toxic effect of heat shock and related stress, we have studied the activity of reporter enzymes during stress. Escherichia coli beta-galactosidase and Photinus pyralis luciferase were synthesized in mouse and Drosophila cells after transfection of the corresponding genes. Both enzymes are rapidly inactivated during hyperthermia. The corresponding polypeptides are not degraded but become insoluble even in the presence of non-ionic detergents. The heat inactivation is more dramatic in vivo within the living cell than in vitro, in a detergent-free crude cell lysate. The extent of enzyme inactivation at a given temperature depends on the cell type in which the enzyme is expressed. Luciferase is inactivated at lower temperatures within Drosophila cells than within mouse cells, whereas beta-galactosidase is inactivated at higher temperatures in E. coli than in mouse cells. A "priming" heat shock confers a transient increased resistance (thermotolerance) of cells against a second "challenging" heat shock. Enzyme inactivation during heat shock or exposure of the cells to ethanol is attenuated in heat shock-primed cells. A comparable thermoprotection is raised by a priming heat shock for both luciferase activity and protein synthesis. Thus, the study of reporter enzyme inactivation is a promising tool for understanding the molecular basis of the toxicity of heat shock and related stress as well as the mechanisms leading to thermotolerance.     

Experimental determination of wall shear rate in canine carotid arteries perfused in vitro

The mathematical model of Hung (Tsai and Hung, 1984) is employed to determine the wall shear rate acting on canine carotid arteries perfused in vitro. Model equations for pulsatile flow in a deformable vessel are coupled with experimental data of dynamic pressure drop, flow rate, vessel radius and radial wall motion. Derived quantities, e.g. velocity profiles and wall shear, are obtained for vessels exposed to 'normotensive' hemodynamics, 'hypertension' simulations and perfusions in which the compliance of the vessel wall is deliberately altered. Our results indicate that wall shear varies markedly as a function of the hemodynamic environment. The effects of vessel radius vs flow rate on the development of wall shear are also demonstrated. It is found that convective processes correlate with the magnitude of wall shear in the 'hypertension' simulations. The present findings and complementary published data may explain, at least in part, the variations in vessel wall transport and endothelial cell biology we observe as a function of the hemodynamic environment. For example we have documented that the exposure of canine carotids to 'hypertensive' (vs 'normotensive') hemodynamics is associated with an increased flux of lipoproteins (LDL) into the intima and luminal media. Alternations in wall compliance, on the other hand, profoundly influence endothelial shape, orientation and cytoskeletal array.     

Characterization of a human homologue of the murine peripheral lymph node homing receptor

Lymphocyte trafficking is a fundamental aspect of the immune system that allows B and T lymphocytes with diverse antigen recognition specificities to be exposed to various antigenic stimuli in spatially distinct regions of an organism. A lymphocyte adhesion molecule that is involved with this trafficking phenomenon has been termed the homing receptor. Previous work (Lasky, L., T. Yednock, M. Singer, D. Dowbenko, C. Fennie, H. Rodriguez, T. Nguyen, S. Stachel, and S. Rosen. 1989. Cell. 56:1045-1055) has characterized a cDNA clone encoding a murine homing receptor that is involved in trafficking of lymphocytes to peripheral lymph nodes. This molecule was found to contain a number of protein motifs, the most intriguing of which was a carbohydrate binding domain, or lectin, that is apparently involved in the adhesive interaction between murine lymphocytes and peripheral lymph node endothelium. In this study, we have used the murine cDNA clone to isolate a human homologue of this peripheral lymph node-specific adhesion molecule. The human receptor was found to be highly homologous to the murine receptor in overall sequence, but showed no sequence similarity to another surface protein that may be involved with human lymphocyte homing, the Hermes glycoprotein. The extracellular region of the human receptor contained an NH2 terminally located carbohydrate binding domain followed by an EGF-like domain and a domain containing two repeats of a complement binding motif. Transient cell transfection assays using the human receptor cDNA showed that it encoded a surface glycoprotein that cross reacted with a polyclonal antibody directed against the murine peripheral lymph node homing receptor. Interestingly, the human receptor showed a high degree of sequence homology to another human cell adhesion glycoprotein, the endothelial cell adhesion molecule ELAM.     

Freezing pattern in apple seeds as affected by the temperature of fruit storage

Storage of apple fruits ( Pyrus malus L. cv. Golden Delicious) at different temperatures (0, 12 and 35°C) markedly altered the pattern of water freezing in the seeds. Higher temperatures of storage brought about a shift from the sequential to the discontinuous type of freezing in seeds, the low temperature exotherm (LTE) being much more pronounced than the high temperature one (HTE). The occurrence of LTE was highly correlated with embryo death. Fruit storage at higher temperatures also caused a decrease in the threshold super cooling temperature of seeds and of naked embryos, removed from the seed coat and endosperm. The decrease was less pronounced in naked embryos than in intact seeds. The results presented show that the frost resistance of apple seeds relies mainly on the supercooling ability of the embryos and is increased by the presence of seed coat and endosperm. The broad peak of the LTE indicates that, in contrast with other seeds and many super cooling organs, massive ice nucleation in apple seeds occurs within the embryo tissues and that extra organ freezing seems to be of less importance. Therefore, the increased super cooling ability of apple seeds, isolated from fruits stored at higher temperatures, seems to rely on those seed properties that protect embryo cells against heterogeneous ice nucleation.     

Influence of gestation on jugular plasma thyroxine levels in Murrah buffalo and Karan Swiss cows

Plasma samples from 106 pregnant Karan Swiss (Brown Swiss x Sahiwal) cows and 108 Murrah buffalo were tested for thyroxine (T(4)) levels to determine the relationship between the hormonal changes and advancing pregnancy in the two species. All samples were collected within 2 months (January and February) to avoid seasonal interference on T(4) levels. In pregnant cows, the concentration of T(4) increased sharply during the first trimester, reaching a peak at the third month of gestation followed by a gradual decline until the last month of pregnancy. In pregnant buffalo, peripheral plasma T(4) levels fluctuated slightly throughout pregnancy without exhibiting a specific trend. Statistical analysis revealed that the magnitude of T(4) levels was significantly lower in buffalo (P < 0.01) than in the cows throughout pregnancy and that the hormonal patterns of the two species were significantly different (P < 0.05) during gestation. It was hypothesized from this study that T(4) requirements for the fetal buffalo calf may be lower than that for the fetal cattle calf since the buffalo gestation period is a month longer and the metabolic rate lower vis-a-vis the cow.