[Selection of mutant branched-chain amino acid producers in the methylotrophic yeasts Hansenula polymorpha]

The object of the work was to test several methods for selection of the methylotrophic yeast Hansenula polymorpha mutants accumulating amino acids with a branched chain (valine, leucine, isoleucine). Selection of strains resistant to norvaline, an analogue of valine and leucine, was found to be the most effective method. The mutants were grown in a medium with methanol and accumulated mainly valine and, in lesser quantities, leucine, isoleucine, aspartate, asparagine and a cysteine derivative. The mutants accumulated up to 110 mg of amino acids per 1 L of the cultural broth, while the wild type strain accumulated only 5 mg/L.