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Two aerobic, gramnegative, red-pigmented, rod-shaped bacteria were compared morphologically and physiologically with Serratia species, which they resembled superficially. The pigment produced by the marine isolates was shown to be similar to prodigiosin, the red pigment of S. marcescens . The isolates had a single polar flagellum, were oxidative, and did not produce acetoin from glucose or reduce nitrates, which made them distinct from both S. marcescens and S. marinorubra . The latter conformed well to the descriptions of S. marcescens in Bergey's Manual . The marine isolates displayed an absolute growth requirement for sea water or its equivalent. The growth requirement for sea water was replaced by sea-water levels of sodium, potassium, and magnesium chloride. Pigment was produced only when this salt mixture was further supplemented with calcium chloride. Neither sea water nor a high salt level was required for growth or prodigiosin synthesis by the Serratia species examined.