The formation of papillae on bacterial colonies. II

Observations are recorded on the formation of secondary colonies of Bact. lactis aerogenes or of Bact. coli mutabile grown on agar plates containing various sugars to which the parti­cular strain requires adaptation. The papillae arise during a process of ageing and may not appear until long after utilization of the specific sugar begins. Cultures derived from papillae show some at least of the adapted or mutant character, but so also may cultures derived from the primary colony. Consideration of colony morphology and of the inhomogeneities which may arise in dense bacterial cultures, suggests that the occurrence of spontaneous mutants is neither a necessary nor a sufficient condition for secondary colony formation.

The formation of papillae on bacterial colonies. I

Observations are recorded of the formation of secondary colonies of papillae on bacterial colonies (mostly of Bact. lactis aerogenes ) grown on solid media containing drugs. The papillae appear to bear no special relation to drug-resistant mutants, since they form in growth on plates containing phenol to which no resistance is developed by the strain of bacteria used. They form only in large, ageing colonies, and when the same total bacterial growth is distributed on the one hand among many small colonies on the plate and on the other hand among a few large ones, it is only in the latter case that the papillae form. Cultures derived from papillae and re-plated sometimes show repeated secondary colony formation and some­times not.