Spontaneous and Induced Color-Variation of the Hy Strain of Serratia Marcescens

Since the elucidation of hereditary mechanisms is dependent largely on the observation of differ-ences and similarities between parents and off-spring, those species which exhibit conspicuous color-variations are often of great value in the perception and solution of genetic problems. For this reason bacteriologists have long recognized the usefulness of the fast growing, pigmented Serratia, and many observations have been made on spontaneous color changes in this species (reviewed by Bunting, 1946). The same proper-ties make it potentially valuable for the investiga-tion of induced mutations. Furthermore, since the organism grows readily on simple synthetic media and is capable of breaking down a very wide variety of organic compounds, it offers excellent material for genetic studies with bio-chemical mutants. Although neither sexual re-combination nor transformation has yet been demonstrated in Serratia, the organism is a gram negative rod closely resembling the coliform bacteria morphologically and physiologically and may well exhibit comparable genetic behavior. It appears, therefore, to be a particularly useful species for the study of many of the genetic problems which are carried out to advantage with bacteria and which promise to shed light not only on microbial phenomena but also on basic genetic mechanisms. Serratia marcescens is the type species in the genus Serratia (Breed et al., 1948) and is reported to be the species used in most genetic studies made with Serratia. However, different strains in the American Type Culture Collection and in various laboratories throughout the country differ markedly in color, stability, morphology, and physiological reactions. At the present time 1 Submitted in partial fulfillment of the re-quirement for a Ph.D. degree at Yale University by the senior author.