VARIATION IN MORPHOLOGY OF COLONIES OF LACTOBACILLI

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Abstract
The morphology of colonies from strains of Lactobacillus lactis and L. helveticus, but not of L. casei and L. bulgaricus, was shown to depend on the composition of agar media and on environmental conditions during growth. Smooth colonies from susceptible strains were favored in agar with an initial pH of about 5 and in agar buffered to stay at that pH value. Smooth colonies were favored also by anaerobic conditions, especially if the pH of the agar was simultaneously reduced. Cysteine or cystine favored smooth colonies but sorbitan monooleate was of doubtful value. The total number of colonies from cultures was unaffected by any of these treatments, and it appears that the smooth colonies did not arise at the expense of rough colonies through a selective action. The smooth colonies that arose under special conditions were unstable and could not be kept smooth when they were returned to a reference medium of carrot-liver agar.