Development of a Highly Efficient Gene Replacement System for an Industrial Strain of Aspergillus oryzae Used in the Production of Miso, a Japanese Fermented Soybean Paste

A homologous gene replacement system was developed for an industrial strain of Aspergillus oryzae KBN630 used in miso production. This system was based on a transformation method involving a bidirectional marker gene, pyrG. To increase the integration of exogenous DNA fragments by homologous recombination, the ku70 gene encoding the Ku70 component of the nonhomologous end-joining machinery was removed from the genome of a pyrG deletion mutant derived from A. oryzae KBN630. The efficiency of homologous integration at the amyR locus was more than 90%.