Colonial Dimorphism in Nonmotile Salmonella.

Enomoto, Masatoshi (National Institute of Genetics, Mishima, Japan) and Tetsuo Iino. Colonial dimorphism in nonmotile Salmonella. J. Bacteriol. 86:473-477. 1963.-Two distinct colonial types, LP-type and SD-type, appeared among the nonmotile mutant clones originated from a strain of Salmonella typhimurium when they were cultivated on semisolid gelatin-agar medium (NGA) at 37 C. These colonial types reflect the nonmotile character of the mutant clones: a nonflagellated clone formed an LP-type colony which was large, translucent, and pale yellowish-gray, whereas a paralyzed flagellated clone formed an SD-type colony which was small, opaque, and dense yellowish-gray. Colonial dimorphism was also present in cells paralyzed by nonheritable change: flagellated cells, immobilized by treatment with homologous anti-H serum, formed SD-type colonies, while cells which had lost flagella, growing in the NGA medium containing 0.12% phenol, formed LP-type colonies. The distinction between the two colonial types was not impaired by addition of motility phage or various sugars to NGA, but became obscure when gelatin was omitted from the medium or the temperature of cultivation was lowered. It is concluded that the difference between the two colonial types is due to the presence or absence of flagella on the surface of the bacterial cells. Such correlation between flagellation and colonial type was observed on nonmotile mutants of several other smooth-type Salmonella strains and Escherichia coli but was not found in a rough-type Salmonella strain.