The two-way selection of mutants and revertants in respect of acetate utilization and resistance to fluoro-acetate in Aspergillus nidulans

Abstract

An extension of two-way selection (i.e. selection of mutant from wild-type and vice versa within the same locus and with the same efficiency) to four different mutational or segregational situations was made possible by using acetate, fluoro-acetate and other substances related to their metabolism.Two types of mutants resistant to fluoro-acetate were selected, the first of which (designated fac) cannot grow on acetate as the sole carbon source, while the second (designated fan) can.Commencing with either a fac or a fan strain a double fac fan strain may be isolated, which is much more resistant to fluoro-acetate than either single mutant strain. Such double mutant strains may also be obtained by crossing a fac to a fan strain. Various characteristics of growth response of these strains on various media were observed.fac mutants are recessive and map in three meiotically unlinked loci, one in linkage group V and two in linkage group VIII.fan mutants are recessive and map in five loci, one in each of the linkage groups V, VII and VIII, and two linked in linkage group VI.Most fac mutants isolated did not revert and this failure is considered genuine. Of the revertants tested, most resulted from extra-cistron suppressors, while revertants of two fac mutants resulted from very closely linked or intra-cistron suppressors.It is argued that the findings indicate the existence of two pathways for acetate utilization in Aspergillus nidulans, a major and a minor; fac mutants are blocked in the major pathway, fan mutants in the minor pathway.