Beschreibung:
<jats:title>Abstract</jats:title><jats:p>Prototrophic revertants were obtained from 4 auxotrophic mutants <jats:italic>A. niger</jats:italic>, 2 of which originated from amylolytically highly active prototroph <jats:italic>A. niger</jats:italic> C, whereas 2 from weakly active prototrophs <jats:italic>A. niger</jats:italic> 23 and 71. A hundred of revertants randomly chosen from each group were initially evaluated with respect to total amylolytic activity. Ten revertants which in this respect reached the highest indices were closely studied in regard to the synthesis of glucoamylase. All of them showed a distinct increase in the activity of this enzyme in relation to their ancestor both auxotrophic and prototrophic. In the case of revertants, derivatives of <jats:italic>A. niger</jats:italic> C prototroph, maximal glucoamylase activity increased over 40%. Among the derivatives of <jats:italic>A. niger</jats:italic> 71 prototroph the increase in glucoamylase activity exceeded many times the level of glucoamylase activity of its prototrophic ancestor.</jats:p>