Utilization ofL- andDL-cystine by the fungusMicrosporum gypseum

Growth of the fungusMicrosporum gypseum and utilization of cystine during this growth was studied in a glucose-arginine medium containing either sodium sulphate, andL-cystine orDL-cystine. Replacement of sulphate withL-cystine brought about no significant changes in the growth of the microorganism. Utilization ofL-cystine as a source of carbon and nitrogen was rapid and complete and excess sulphur was excreted into the medium in the form of sulphate. Similarly excreted were also minute amounts of sulphite which immediately reacted with the remaining cystine to formS. sulphocysteine. Growth ofM. gypseum in a medium withDL-cystine was slow. Although this substance was not utilized as readily asL-cystine, its utilization was still complete and excess sulphur was similarly excreted in the form of sulphate and sulphite. The initial step in the utilization of theD-isomer is probably its extracellular deamination.