Hereditary variation and genetic recombination in Koji-molds (Aspergillus oryzae and Asp. sojae). I. Natural...

Area of Science:

• Microbiology
• Mycology
• Food Science

Background:

• Koji-molds, including Aspergillus oryzae and Aspergillus sojae, are crucial in fermented food production.
• Natural variation within these fungal species can impact their industrial applications and genetic stability.

Purpose of the Study:

• To investigate and categorize the natural variation observed in monospore lines of Koji-molds.
• To differentiate between stable and unstable strains regarding variant production.

Main Methods:

• Isolation and culturing of 58 Koji-mold strains from various sources.
• Successive single spore culture to assess strain stability.
• Observation and classification of colony morphology and variant types (e.g., C-type, X-type, LS, Nit).

Main Results:

• Koji-mold strains were divided into two groups: inconstant (prone to variation) and constant.
• Inconstant strains (X-type) exhibited varied conidia and mycelium proportions, often producing larger conidia.
• Constant strains (C-type) showed abundant conidia and smooth surfaces, with smaller conidia.
• Identified variant colony types include Conidial (C), Mycelial (M), Restricted (R), Sterile (St), Nitrate-requiring (Nit), and Semi-lethal (LS).
• Pedigree cultures of inconstant strains did not reveal definite segregation ratios for variant types.
• LS and Nit types frequently arose spontaneously from the M-type.

Conclusions:

• Significant natural variation exists within Koji-mold monospore lines.
• The genetic instability of certain strains, particularly the inconstant types, presents challenges for consistent industrial use.
• Further research is needed to understand the genetic mechanisms underlying variant production in Aspergillus species.