Yeast cell mortality related to a high-pressure shift: occurrence of cell membrane permeabilization

The shrinkage of yeast cells caused by high-pressure treatment (250 MPa, 15 min) was investigated using direct microscopic observation. A viable staining method after treatment allowed the volume variation of two populations to be distinguished: an irreversible volume decrease (about 35% of the initial volume) of pressure-inactivated cells during pressure holding time, and viable cells, which were less affected. A mass transfer was then induced during high-pressure treatment. Causes of this transfer seem to be related to a pressure-induced membrane permeabilization, allowing a subsequent leakage of internal solutes, where three ions (Na+, K+ and Ca2+), plus endogenous glycerol, were verified. This glycerol leakage was found to occur after yeast pressurization in a medium having low water activity, although the yeast was not inactivated. All these observations lead to the hypothesis that pressure-induced cell permeabilization could be the cause of yeast inactivation under pressure.     

Schriftenschau

Ohne Zusammenfassung     

Modeling Tetrahymena thermophila growth and protease production

Oxygen concentrations stimulated growth (maximum number of cells) and protease secretion by Tetrahymena thermophila. Agitation and aeration conditions for growth and protease secretion were optimised by a central composite design. The best optimised combination was a stirrer speed of 338 rpm and an aeration of 1 vvm. Journal of Industrial Microbiology & Biotechnology (2000) 25, 58–61. Received 24 September 1999/ Accepted in revised form 06 March 2000     

A rapid colorimetric assay for heparinase activity.

A rapid, sensitive, assay for enzymes that degrade heparin is described. The procedure is based on the interference of heparin with color development during the interaction of protein with the dye Coomassie brilliant blue. The loss of this property when the glycosaminoglycan is degraded by heparinase can be used to quantify activity of the enzyme in pure form, or in complex biological samples such as tissue homogenates or serum. The assay is also suitable for studying dependence of heparinase activity under conditions such as varying pH and temperature.     

Amperometric alcohol electrode with extended linearity and reduced interferences.

Conventional amperometric alcohol electrodes were constructed with oxygen- and hydrogen peroxide-base sensors and a much improved electrode was designed by placing a hydrophobic, gas-permeable membrane over the conventional hydrogen peroxide-based alcohol electrode. The immobilization of alcohol oxidase with glutaraldehyde was also studied and optimized. The upper linear ranges of the conventional and newly designed alcohol electrodes were 0.02 and 0.5% ethanol, respectively. The hydrophobic membrane of the new design eliminated the classical electrochemical interferences of hydrogen peroxide-based electrodes and the typical pH dependence of enzymatic systems.     

Procedure and Analysis of a Useful Method in Determining Mycelial Dry Weights from Agar Plates

The evaluation of growth by dry weight determination of fungus mycelium for agar plates was examined. The data obtained were statistically analyzed. This method was shown to be sufficiently accurate to be used as an investigative tool.     

Feasible mechanisms for algal digestion in the king angelfish

To determine the ability of the king angelfish Holacanthus passer to digest algae, three algal species were immersed in acidic conditions similar to that found in the stomach of fish. Only one of them was not susceptible to acidic lysis; two were affected after 40 and 60 min at pH 2·0. King angelfish have an expanded region of the intestine called here the hindgut chamber (HC) containing populations of micro-organisms. Some of these micro-organisms have the capacity to grow in cellulose, agar, and alginic acid; the main components of algal cell walls. Micro-organisms grew in carboxymethylcellulose cultures under aerobic and micro-aerobic conditions. The HC is highly vascularized, which could increase absorptive efficiency of material digested in it.     

Heat treatment results in a loss of transgene-encoded activities in several tobacco lines.

Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum) plants led to a reversible reduction or complete loss of transgene-encoded activities in about 40% of 10 independent transformants carrying the luciferase-coding region fused to the 355 cauliflower mosaic virus or the soybean small subunit promoter and the nopaline synthase promoter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of the lines, temperature sensitivity of the transgene-encoded activities depended on the stage of development, occurring in either seedlings (40% luciferase and 50% neomycin phosphotransferase) or adult plants (both 40%). The phenomenon did not correlate with copy numbers or the homo- or hemizygous state of the transgenes. In lines harboring a temperature-sensitive luciferase activity, reduction of bioluminescence was observed after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reaction to the heat treatment, the level of luciferase RNA was slightly increased at 37 degrees C. Only in lines showing temperature sensitivity of transgene-encoded activities was the amount of luciferase and neomycin phosphotransferase strongly reduced. In sterile culture, heat treatment for 15 d did not cause visible damage or changes in plant morphology. In all plants tested a slight induction of the heat-shock response was observed at 37 degrees C.