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Newsletter Oktober 2009 |
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Because of their simplicity shaken bioreactors are often underestimated and operated under unsuitable “standard” conditions without precise knowledge about the physical parameters which characterise the culture conditions.
This publication highlights the advantages and problems of shaken cultures with graphically presented examples. In particular the impact of the oxygen transfer rate is brought to the reader’s attention.
According to the author, experiments in shaken bioreactors are not significant if an oxygen deficiency disguises the impact of other parameters. Hence, screening for new metabolites, or the investigation of the effects of different media compositions on the cells, is impeded.
It was shown that stopping the shaker for a short time in order to take a sample interrupts the oxygen supply and thus the breathing activity of the culture, with lasting effects on the microbial metabolism. “Dr. Shaker” gives advice on how to get round this problem (s.u.).
Furthermore this paper shows the influence of the concentrations of different substances on the oxygen transfer rate in a shaking flask. Recognition of this phenomenon means misinterpretations of experimental results can be anticipated.
In our free publication database you will find abstracts and links for this paper and most of the articles cited in it.
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| Dr. Shaker´s helpful hint no.1 |
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Sometimes less is more To ensure good aerobic cultivation conditions in the shake flask, the ratio of liquid volume to flask size should be proportional.
The liquid volume for cultivation of respiratory active microorganisms like Escherichia coli should not exceed 5 - 10 % of the total flask volume (i. e. 10 to maximum 25 mL in a 250 mL flask) otherwise there may be a lack of oxygen supply.
Recommended culture conditions for the aerobic cultivation of E. coli in a 250 mL wide neck flask with cotton plug or membrane cap (s.u.) are: 10 mL filling volume 300 rpm shaking speed 50 mm shaking diameter Microorganisms with minor breathing activity, like yeasts or filamentous fungi should be cultivated as follows: 250 mL wide neck flask with cotton plug or membrane cap (s.u.) 25 mL filling volume 300 rpm shaking speed 50 mm shaking diameter For plant or animal cell culture the following conditions should be chosen:
disposable shake flask with membrane cap or narrow neck flask with cotton plug controlled humidity to reduce evaporation loss 50 - 100 mL filling volume 100 - 150 rpm shaking speed 50 mm shaking diameter Sampling reduces the filling volume of the flask and thereby changes the cultivation conditions. Usually the shaker is stopped during the sampling procedure resulting in an interruption of oxygen supply. This may influence the total metabolic activity of the cells.
To minimize the impact of this procedure on experimental results an appropriate number of flasks should be scheduled. One entire flask can then be harvested for sampling, the shaker is stopped for only a short period of time and the oxygen supply of the cells is guaranteed. |
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