Studies on the Natural Variation of Koji-molds (Asp. oryzae and Asp. sojae)

Part 12. Genetic Studies of Heterocaryosis by using Biochemical Mutants (Double-less Strains)

Abstract

1. The leucineless and histidineless mutant strains of Asp. sojae; which, had been known to be comparatively stable, were irradiated with ultraviolet rays, and the following double auxotroph is mutants were isolated.
From 1OS his* strain; reduced nitrate (11 strains), a rgininelessr⁽¹⁾, and. methionineless⁽¹⁾.
From 14S leu**strain; reduced nitrate⁽²³⁾, arginnineless⁽¹⁾, histidineless⁽¹⁾, lysineless⁽¹⁾, methionineless⁽²⁾, nicotinic-acidless⁽¹⁾, and adenine or hypoxanthineless⁽¹⁾-(Table 2).
2. As to the genetic markers such as colony type and nutrient requirement, 10 double-less-Mutant strains excepting reduced nitrates, were proved to be more stable than single-less mutant strains.
3. Allelism-tests were carried out in every combination of 3, arginineless strains, 3 methio. nineless strains, and 4 histidineless strains, by prototrophic heterocaryon method. with the results that the strains belonging to the two formers were observed to be non-allelic each other and the latter (histidineless mutants) were allelic.
4, Prototrophic heterocaryon-tests between 3 tester strains originating from 10S his and 6 auxotrophs from 14S leu were performed. The frequencies of prototrophic heterocaryon forma-tion were found to be 0.5_??_8.9%, indicating that there is little difference between single-less (0.4_??_4.8%) and these double-less mutants.
5. The heterocaryons formed between wild type tester strains and mutant strains were pro-ved to have the character of wild type in their phenotypes such as colour of colony, sporulation, and growth factor etc.
Therefore, it may be reasonable to say that wild type characters are dominant to mutant ones so far as the above mentioned characters concerned.
* (Sporogenous type, histidineless) ** (Sporogenous type, leucineless)