Interspecific Hybridization of Aspergillus usamii mut. shirousamii and Aspergillus niger by Protoplast Fusion

Abstract

The protoplast fusion technique has been applied successfully to Aspergillus usamii mut. shirousamii and Aspergillus niger, leading to the recovery of recombinant progeny. A strain obtained from a heterokaryon using ^/-camphor showed a 2-fold DNA content per conidium and an about 1.2- fold conidial diameter compared to those of the original strains, and was regarded as a heterozygous diploids. The diploid strain was treated with benomyl as a haploidizing agent, many segregants being obtained. The segregants were phenotypically single and double auxotrophs, and prototrophs. The prototrophic segregants were selected and their haploidy was confirmed by their conidial sizes and DNA contents per conidium. A prototrophic segregant strain derived from these haploids was considered phenotypically to be a recombinant with some excellent characteristics, that is, higher amylase and citric acid productivities than those of the original strains. The results indicate that the segregants of diploid strains induced by benomyl cause genetic changes affecting enzyme and citric acid production.