The Effect of Carbonation, Benzoic Acid and pH on the Growth Rate of a Soft Drink Spoilage Yeast as determined by a Turbidostatic Continuous Culture Apparatus

Summary: A turbidostatic continuous culture apparatus is described, which has been used to determine the effect of variations in carbonation, benzoic acid and pH on the growth rate of a soft drink spoilage yeast. Results are presented and a model is derived which, it is believed, enables the spoilage potential of many carbonated soft drinks to be predicted.     

Action of diphtheria toxin does not depend on the induction of large,stable pores across biological membranes

Summary Vero cells exposed to diphtheria toxin at pH 4.5 leak monovalent cations but not amino acids or phosphorylated metabolites; affected cells do not take up trypan blue. Monovalent cation leakage is inhibited by 1mmCd²⁺, but not by 1mmZn²⁺ or Ca²⁺. Cd²⁺ blocks calcein leakage from liposomes and closes diphtheria toxin-induced channels in lipid bilayers. It is concluded that translocation of the A fragment of diphtheria toxin across biological membranes does not depend on the formation of large stable pores, but that small Cd²⁺-sensitive pores may play a role.     

Staphylococcus aureus alpha-toxin-induced pores: Channel-like behavior in lipid bilayers and patch clamped cells

The conductance of pores induced by Staphylococcus aureus -toxin in Lettre cells has been compared to that in bilayers composed of synthetic lipids or Lettre cell membrane constituents. Previously described characteristics of toxin-induced conductance changes in lipid bilayers, namely rectification, voltage-dependent closure, and closure at low pH or in the presence of divalent cations (Menestrina, 1986) are displayed also in bilayers prepared from Lettre cell membranes and in patch clamped Lettre cells. It is concluded that endogenous proteins do not affect the properties of -toxininduced channels significantly and that the relative lack of ion channels in Lettre cells makes them ideal for studies of pore-forming toxins by the patch clamp technique.Dr. Sviderskaya is on leave of absence from the Physiology Institute, University of St. Petersburg, RussiaWe are grateful to Dr. J.P. Arbuthnott and Dr. K. Hungerer for gifts of S. aureus -toxin, to Dr. T.B. Bolton for collaboration with patch clamped cells and to Dr. J.M. Graham for help with the preparation of Lettre cell plasma membranes. This study was supported by the Cell Surface Research Fund, Medical Research Council, Science and Engineering Research Council, UNESCO (Molecular and Cell Biology Network) and The Wellcome Trust.     

Oscillations of redox states in synchronously dividing cultures of Acanthamoeba castellanii and Schizosaccharomyces pombe.

The redox state of the mitochondria of Acanthamoeba castellanii and Schizosaccharomyces pombe was assessed with a flying-spot fluorometer (Chance et al. 1978. Am. J. Physiol. 235:H 809) that provides excitation appropriate for oxidized flavoprotein or reduced pyridine nucleotide. Fluorescence signals could be resolved from the thin films of cultures that were only one cell deep. In both organisms anoxia was associated with an increased pyridine nucleotide and decreased flavoprotein fluorescence. The addition of mitochondrial uncoupling agents increased the flavoprotein fluorescence and the fluorometer was able to resolve uncoupler-sensitive and uncoupler-insensitive fractions of S. pombe cultures. In both synchronous and asynchronous cultures of A. castellanii and S. pombe the mitochondrial redox state oscillates with a period of 4.5 +/- 1.0 min. Oscillations with much longer period, of the order of an hour, are observed in synchronous cultures and these oscillations correlate with similar oscillations in respiratory rate, uncoupler sensitivity, and adenine nucleotide pool sizes. The results are consistent with the hypothesis that synchronous cultures of A. castellanii and S. pombe oscillate between the ADP-limited (state 4) and ADP-sufficient (state 3) respiratory states, i.e., exhibit in vivo respiratory control.     

Scanning ion conductance microscopy of living cells.

Currently there is a great interest in using scanning probe microscopy to study living cells. However, in most cases the contact the probe makes with the soft surface of the cell deforms or damages it. Here we report a scanning ion conductance microscope specially developed for imaging living cells. A key feature of the instrument is its scanning algorithm, which maintains the working distance between the probe and the sample such that they do not make direct physical contact with each other. Numerical simulation of the probe/sample interaction, which closely matches the experimental observations, provides the optimum working distance. The microscope scans highly convoluted surface structures without damaging them and reveals the true topography of cell surfaces. The images resemble those produced by scanning electron microscopy, with the significant difference that the cells remain viable and active. The instrument can monitor small-scale dynamics of cell surfaces as well as whole-cell movement.