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The production of mutant strains of Photobacterium fischeri has been reported by McElroy and Farghaly (1948), who succeeded in isolating amino acid mutants following exposure to ultraviolet radiations. The examination of such mutants as these may prove to be of value in the study of the relationships between respiratory and luminescent systems within the cells. In the course of studies upon the respiration of Photobacterium fischeri it was necessary occasionally to reisolate in order to maintain a pure culture. This was accomplished by the conventional plating method. Brightly glowing colonies picked from the agar surface were transferred to slants of a complete medium for use as stock cultures. This report deals with a purine-requiring mutant strain of this organism which was isolated in the foregoing manner from the parent culture.' The failure of a basal medium described and used by Doudoroff (1942) to support growth of this organism,2 led to the investigation of its nutritional requirements. It was discovered that growth occurred only in the presence of one of the following purine bases: adenine, hypoxanthine, guanine, or xanthine. The extent of growth was found to be proportional to the amount of purine present. There are descriptions in the literature of purines that may function as essential growth factors or stimulatory substances for particular organisms. Guthrie (1949) has described an Escherichia coli mutant that possesses purine requirements quite similar to those of the P. fischeri mutant described here. Tatum (1946) produced a mutant strain of E. coli which required purines, and Pappenheimer and Hottle (1940) found a strain of hemolytic streptococcus with a purine requirement. Mitchell and Houlahan (1946) produced a Neurospora mutant deficient for both adenine and hypoxanthine, and these investigators have proposed this mutant for use as an assay organism.

A PURINE-REQUIRING STRAIN OF PHOTOBACTERIUM FISCHERI