Breeding of New Koji-molds through Interspecific Hybridization between Aspergillus oryzae and Aspergillus sojae by Protoplast Fusion

Abstract

Interspecific protoplast fusion between Aspergillus oryzae and Aspergillus sojae and subsequent haploidization of the fusants were done to search for a further possibility in breeding of new Aoyr-molds for soy sauce fermentation. Fusion between the yellow-spored, met- mutant of A. oryzae and the white-spored, bio- mutant of A. sojae produced green-spored-fusants on the minimal medium with a frequency of 5 × 10-5 per protoplast pairs. The fusants, which were thought to be heterokaryons for their frequent segregation of the parental marker strains, could be stabilized through repeated subcultures. The resulted green-spored-diploids were haploidized with benomyl, and a variety of phenotypes including recombinants were obtained. The haploidized recombinants were obtained with a frequency of 0.97-1.25×10-1. Behaviors Of some phenotypic properties in the fusants and the haploidized segregants were investigated. Although markers of conidial color and auxotrophies were complemented in the fused diploids, the morphology of conidial walls of only A. oryzae-type (rough) or A. sojae-type (echinulate) was observed in the diploids and no intermediate type appeared. Gel electrophoresis of the extracellular alkaline proteinases from the diploids and the haploidized recombinants showed that they produced one of the A. oryzae type or A. sojae type but not both. © 1990, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.