麹菌の自然変異に関する研究

Abstract

(1) Natural variation in monospore lines of Koji-molds (Asp. oryzae, Asp. sojae and its related strains) isolated from the commercial Koji materials or soils and from the stock cultures of the authors' laboratory has been observed. (2) There seem to be two groups of strains in. about 100 strains of Koji molds investigated, one group consists of inconstant strains which are very liable to produce natural variants and the other consists of the strains which remain constant through many generations. (3) The inconstant strains exhibit conidia bearing partly floccose colonies (X-type). They form generally large conidia. (Asp. oryzae var. magnasporus(1) and some members belonging to Asp. oryzae s. str. which produce large conidia occasionally). The colonies of the constant strains show abundant conidium formation and smooth surface (S type or sporogenous type). Sizes of the conidia are mostly small (Asp. oryzae var. microsporus(1)) or medium (Asp. oryzae s. str.). (4) The variations are more frequent among so called “wild strains” isolated from soils or Koji factories than among the strains from stock cultures, or “culture strains” (5) The colony types of the variants on Czapek agar are as follows: S (sporogenous, whole surface covered with conidia), F (floccose), FR (F-restricted), FN (floccose but very faint growth upon Czapek agar, or nitrate less assimilative strains(2)), N (no growth on Czapek agar, or nitrate non-assimilative, ) LS (semi-lethal, or growth being stopped directly after germination), L. (lethal, or no growth on any media). (6) Pedigree cultures of 8 incostant strains have been carried out, but no definite segregation ratios of each variant type has been recognized through successive generations. (7). Strains belonging to each variant type have ordinarily become constant or fixed after 5 or 6 generations of pedigree cultures which were carried out at the intervals of 10_??_14 days, 80_??_100 colonies by monospore culture being taken at each generation. From old cultures of some fixed strains which have-been kept for about 5 months at room temperature, remarkable segregations have again been recognized. (8). The LS or L type strains have commonly been obtainable from the. strains of the F-type.