Genetic improvement and production of lysine-rich yeast
1993
Touchapon Rupasut
Lysine is an essential amino acid for human and animals. It may intakes in the form of pure amino acid and diet with high lysine content, such as adding yeast cell into the diet. However yeast cell contained high amount of nucleic acid which may cause problem to the one who take it. Therefore, increasing of lysine content of yeast cell is necessry. Of various methods to increase the lysine content of yeast genetic improvement by mutation was used in this study. Cells of Saccharomyces cerevisiae B120 were mutagenized by NTG and 2,000 colonies of survival cells were screened for the lysine rich mutant. The mutant RL-6 which showed highest lysine content was selected. The mutant RL-6 was cultured in Erlenmayer flask with rotary shaking incubation the highest lysine content of 79.6 microg/ml was obtained by using the medium contained 2.0 % glucose, 0.1 % ammonium nitrate, pH 5.0 and incubation at 35 deg C for 96 hrs. While the wild type, S. cerevisiae B120, revealed highest lysine content of 14.0 microg/ml when cultivated in the medium contained 1.0 % glucose, 0.5 % urea, pH 5.0 and incubated at 35 deg C for 120 hrs. When the mutant RL-6 was cultivated in a jar-fermentor with various agitation speed and aeration rate, the highest lysine content of 121.8 microg/ml (12.1 mg lysine/g cell) was obtained after 48 hrs cultivation when 600 rpm agitation speed and 1.0 vvm aeration rate were used.
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