Abstract
A number of small-colony variants of the G-type were isolated from plates streaked with 2- to 5-month cultures of S. paradysenteriæ Sonne. These variants occurred irregularly and infrequently — to the extent of one per cent of the colonies counted. Cells possessing the potentiality of developing G-colonies were not encountered in 18- to 24-hour cultures. The variants produced colonies from 0.04 mm. to 0.20 mm. in diameter. In microculture the normal cell divided by a process similar to budding while the variant divided by simple transverse fission. The minimal reproductive time of the normal was about 36 minutes and that of the variants from one hour and 45 minutes to 3 hours and 54 minutes.
Reversion of the variants to the large-colony or normal form was brought about by cultivating in serum-enriched media, incubation for 5 days or by 15 to 20 serial transfers in nutrient or veal-infusion-broth. After reversion, normal biochemical, serological and cultural characteristics were reëstablished. Some strains, while believed to be true variants, could not be made to revert completely to the normal colonial size.
The biochemical activity of the variants was greatly reduced as compared to the normal. Sugars were fermented very slowly and in some cases not at all. The variants often required 10 to 30 days to produce acid in some sugar-broths. The addition of serum to, the medium usually resulted in better growth and fermentation of a wider range of sugars.
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