Abstract
A strain of mutabile type (M) variant was obtained from each of the 3 strains of E. coli. When these M variants were cultivated in galactose peptone (GP) water, they were divided into 3 groups: (a) difficult to produce galactose fermenting daughter type variant (RT), (b) relatively easily produce them and (c) very easily produce them. Employing the last one, the author investigated as to whether the RT variant is derived from M variant or from daughter mutabile type (MT) variant. The results thus obtained revealed that RT variant is derived from M variant. When the above stated 3 strains of M variant were cultivated on galactose casamino medium containing B. T. B., which is extremely inhibitory to the growth of M variant, yellow colonies grew on the plate in addition to those of MT variant. This yellow growth was proved to be what Fukutome and his co-workers have named RT variant. The rate of appearance of RT variant was found related to the degree of the fermentation of GP water by M variant, The number of colonies of RT was in proportion to the bacterial number of the inoculum. For instance, when the bacterial concentration of the 10-3 dilution of M variant suspension was at the order of 100, 000 per cc, several colonies of RT variant appeared. In other words, RT variant appeared at the rate of 1/100, 000 of the bacterial number of M variant. When the dilution was more than 10-4, RT variant hardly appeared. Furthermore, the number of colonies appeared was not found increased according to the lapse of incubation period. Reviewing the results of the present work, the author found that his findings well coincide with the observations by Ushiba and his co-workers on MT variant, excepting that the rate of mutation differs according to varying strains. Generally, in most cases, the rate was much lower compared with that of the mutation to MT variant. This problem will be further investigated in a later report.
