ASSOCIATION OF COLONY VARIATION IN SERRATIA-MARCESCENS WITH THE DIFFERENTIAL EXPRESSION OF PROTEASE AND TYPE-1 FIMBRIAE

Several clinical isolates of Serratia marcescens were found to dissoci ate on peptone glycerol agar into colonies with red and pink or white and gray phenotypes that differ in the expression of proteolytic activ ity and mannose-sensitive type of hemagglutination. Colonies of red an d white type were proteolytically active but did not express hemagglut ination, whereas pink and gray colonies were protease-deficient but ag glutinated guinea pig erythrocytes. Site-directed mutagenesis of a red laboratory strain S. marcescens SM6 resulted in selection of protease negative derivative prt::G7 which expressed the pink phenotype with h emagglutinating activity. It is suggested that a DNA-regulatory elemen t may be involved in this type of colony variation.