Yeast lysis structures

The two models of yeast lysis presented here have been developed to serve two different purposes. The simple model is a lumped, two-step model which follows the major features of the data and may prove useful for design of lysis reactors. The structured model, which can account for the source of protein within the cell, was developed to gain a mechanistic basis for predicting the effects of untested process conditions, and to aid insight into the physical processes at work during lysis. 

The simple and structured model simulations for yeast mass and soluble protein, peptides and carbohydrates are compared in Figure 6 for the yeast and enzyme concentration shown in Figures 3 and 4, and in Figure 7 for a concentrated yeast cell slurry. The simple model fits the data fairly well at both yeast concentrations, in every variable except the peptides. The fit for all variables at longer reaction times is directly related to use of the extent-of-reaction term Y , in the yeast lysis equation. 

Figure 5 Structured model simulation of yeast lysis 5a Cell structures...

Flash-pasteurization (heating between 72 and 76°C for 20 seconds) seems to be effective. It improves the fermentability of wines with stuck fermentation (Dubemet, 1994). This operation is valid for red, rose and dry white wines and should be carried out before inoculating. Its heating effect can be likened to the effect observed during thermo-vinification (Section 12.8.3). In spite of the destruction of yeasts, the heated musts ferment especially well. The effects of this process merit further study but several explanations can be proposed fermentation by a sole strain avoiding microbial antagonisms addition of nntri-tive elements due to yeast lysis elimination of toxic substances and modification of the colloidal structure. 

Many cells are susceptible to the appreciable shearing forces that arise on repeated freezing and thawing, or to hypotonic buffers which cause cells to swell up, and in certain cases to lyse this is particularly the case for cells in soft plant and animal tissue. Such treatments only rarely lead to complete cell lysis, the exceptions to this being erythrocytes and reticulocytes which are lysed quantitatively under hypotonic conditions. Non-mechanical homogenisation is of particular relevance to cells like yeast which are refractory to other procedures. One of the simplest procedures for yeast, which can certainly not be described as gentle, is toluene-induced autolysis. This is carried out at room temperature and leads to permeabilisation of the cell walls this causes various hydrolases to be activated causing breakdown not only of the cell structure, but also (undesirably) of many sensitive proteins and nucleic acids in the cell. Consequently, this process is mainly of historical interest. 

Structured and Simple Models of Enzymatic Lysis and Disruption of Yeast Cells... 

Hunter, J.B. and Asenjo, J.A., "A structured, mechanistic model of the kinetics of enzymatic lysis and disruption of yeast cells", Biotechnol. Bioeng., 1986 (being submitted). 

Papulacandin B, an antibiotic produced by the deuteromycete Papularia sphaerosperma, inhibits the growth of yeasts, but has no effect on other fungi, bacteria, or protozoa.The mode of action involves the inhibition of synthesis of alkali-insoluble jS-D-glucan of Saccharomyces cerevisiae and Candida albicans in sphaeroplasts and causes lysis of cells by osmotic rupture.Echinocandin B and a structurally related antibiotic aculeacin A also inhibit j3-D-glucan synthesis in yeast, possibly in a similar manner.Papulacandin B has been shown to inhibit the transfer of D-glucose from UDP-D-glucose, but not D-mannose from GDP-D-mannose, into dolichyl phosphate. 

Li and Harrison carried out the first cell assay in microchannels [2]. This seminal work made use of electrokinetically driven flow (electroosmosis and electrophoresis) to transport bacteria, yeast, and mammalian cells in channels and to implement low-volume chemical lysis (cell death). This theme of microfluidics-based cell transport, sorting, and lysis has continued to be a popular application, as well as related work in using microfluidics to culture cells and to pattern them into structures. The utility of these methods is acknowledged (and that they are featured in several good reviews [1] and other entries in the encyclopedia) but focuses here on describing microfluidics-based cell assays that fit the definition described above - application of a stimulus and measurement of a response. 

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