Mutant strain
Japanese: 変異株（ミュータント）
A microbial strain with naturally or artificially altered DNA sequences. Created through UV irradiation, chemical mutagenesis, genome editing, etc., used for breeding superior industrial strains.
A mutant strain is a microbial strain whose DNA sequence has changed, either spontaneously or artificially. Microbial genes constantly undergo small changes from UV radiation, reactive oxygen, and DNA replication errors. Identifying individuals with useful traits among these changes is the process of mutant strain breeding.
White koji mold was discovered as a natural mutant of black koji mold. Citrinin-free strains of red koji mold were also developed through breeding techniques.
Today, in addition to classical methods like UV irradiation and NTG (chemical mutagen) treatment, genome editing technologies such as CRISPR-Cas9 enable more precise introduction of mutations.
The evolution of fermentation is also a history of microbial mutation and selection. The act of a brewery master selecting good microbes was, without conscious awareness, a screening of mutant strains.