Isolation of auxotrophic mutants ofAspergillus niger by ethylmethane sulphonate treatment

The alkylating agent EMS can be employed for the isolation of auxotrophic mutants of theAspergillus niger strain K 10. The maximum number of auxotrophic mutants (2.9–5.1%) corresponded approximately to the number of mutants obtained by EMS treatment of yeasts, but it was by order lower than the number of mutants generally obtained by EMS treatment in bacteria. The majority of isolated mutants grew worse than the parent strain in the liquid medium and also formed lower amount of organic acids. The organic acid which was most frequently accumulated by mutants was citric acid.