Saccharomyces cerevisiae operation

Effluent is drawn off from a side port. Under conditions in which a conventional three-phase fluidized bed bioreactor operated in an unstable manner because of gas logging, the new bioreactor converted glucose to ethanol at a 27% higher rate. Saccharomyces cerevisiae was grown in alginate beads for this reaction. 

Biosynthesis.—Ubiquinone. The identification of 3,4-dihydroxyhexaprenylben-zoate (162) in a Saccharomyces cerevisiae mutant strain that cannot synthesize ubiquinone suggests that (162) may be an intermediate in ubiquinone-6 biosynthesis in eukaryotes, in contrast to the pathway via 2-polyprenylphenol which operates in prokaryotes. In mammalian systems alternative routes have been discussed for ubiquinone biosynthesis in rats." Some properties of mitochondrial 4-hydroxybenzoate-polyprenol transferase have been described."" ... 

The rate constant k at typical operating pressures of 500-1000 bar is found to be proportional to the pressure raised to a power a dependent on the organism (a =2.9 in Saccharomyces cerevisiae and 2.2 in Escherichia coli (Hetherington, 1971) a= 2.5... 

A set of alcoholic fermentations experiments was conducted in order to verify the performance of the model-based substrate sensor. Diluted molasses was used in the experiments as feed substrate and bread yeast, Saccharomyces cerevisiae, as inoculum. The operational conditions and kinetic parameters used are given in Table 1 for two different experiments (tests 1 and 2), and values of ethanol and biomass concentrations were also determined off-line using gas chromatography (CG) and dry cell weight standard (7) methods, respectively. 

Alumina and other ceramic membranes of various microfiluaiion pore sizes have been used for the separation of yeast (saccharomyces cerevisiae) from the broth and the clarification of thin stillage [Cheryan, 1994]. A typical flux of 110 L/hr-m can be obtained with a crossflow velocity of 4 m/s and a transmembrane pressure of 1.7 bars. The crossflow velocity is found to markedly affect the membrane flux. Concenuation factors (ratios of final to initial concentrations) of 6 to 10 for both the broth and the stillage can be achieved. Backflushing with a frequency of every 5 minutes and a duration of 5 seconds helps maintain the flux, particularly in the initial operating period. The permeate flux for both types of separation reaches steady state after 30 to 90 minutes. 

A highly specific hydrolysis of sucrose could also be achieved by use of invertase from Saccharomyces cerevisiae (P-o-fructofuranosidase). Nevertheless high enzyme costs and the batch-wise operation mode proved economically disadvantageous over the ion exchange process. 

Guillas, L, Kirchman, P.A., Chuard, R., Pfefferli, M., Jiang, J.C., Jazwinski, S.M., and Conzelmann, A. C26-CoA-dependent ceramide synthesis of Saccharomyces cerevisiae is operated by Laglp and Laclp. Embo J, 20, 2001, 2655-2665. 

Continuous SSF processes are usually operated in plug flow mode. Such processes will require pasteurization or sterilization of the substrate as it enters the bioreactor, mixing with an inoculum, and at the outlet end of the bioreactor, continuous removal of spent substrate. Such a process was operated on a pilot scale for the production of ethanol from fodder beets by Saccharomyces cerevisiae [81,82]. The bioreactor had a screw within a 4.7 m long and 15.25 cm diameter tube. The screw was rotated intermittently to mix the substrate and move it along the tube. At the front end was a hammer-mill and a pasteurization chamber for substrate preparation and a port for inoculation. New substrate was added, inoculated, and the screw rotated at 12-h intervals, resulting in a residence time of 72 h. 

Systematic investigations of microbial cell recovery by foam flotation were performed by Hansenula polymorpha [113-117] and Saccharomyces cerevisiae [ 118 -123] in continuous operation. The equipment used for flotation was often identical to that used for protein flotation. The microorganisms were cultivated in laboratory reactors on synthetic media in the absence of antifoam agents in continuous operation and the cell-containing cultivation medium was collected in a buffer storage and was fed into the middle of the colunm, at the top of the interface between the bubble and the foam layers. The height of the interface was controlled by an overflow. The foam left the colunm at the top. The cells were recovered from the foam liquid by a mechanical foam destroyer. The liquid residue left the column through an overflow [113] (Fig. 6). 

Hansenula polymorpha and Saccharomyces cerevisiae were cultivated on synthetic medium with 1% glucose in fed-batch and continuous mode, respectively, in the absence of antifoam agents. For the nutrient preparation, sterilization and storage, 300-, 600-, 1000- and 5000-1 stirred tank vessels were used. The nutrient salt medium was steriUzed without glucose. The glucose solution was autoclaved separately and was added to the cold, sterilized nutrient medium. The flotation column was operated in continuous mode. 

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