Selection of amino-acid overproducer yeast mutants
1992
Martinez-Force, E. | Benitez, T.
Mutants resistant to ethionine, a toxic analog of methionine, were selected by subjecting yeast cells to competition experiments under continuous culture, controlled by pH, with a wide range of increasing ethionine concentrations. The mutants accumulated up to over 30 mM methionine and were able to grow in ethionine concentrations from 0.5 to 50 mM, whereas the wild-type strain stopped growing at 0.1 mM ethionine, and its free methionine pool was 0.2 mM. From ethionine-resistant mutants, strains able to overproduce threonine were isolated by selecting either in continuous or in batch cultures, the latter supplemented with 0.1-5 mM hydroxynorvaline, a toxic analog of threonine. These mutants accumulated up to over 200 mM of threonine (the internal pool of threonine in the wild-type was around 5 mM), grew in minimal medium with growth rates similar to that of the wild-type, accumulated the analogs at internal concentrations proportional to the external, and accumulated other amino acids such as homoserine, aspartate, isoleucine and S-adenosyl-methionine.
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