Utilization of cystine by dermatophytes on a gelatin medium

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Abstract
All 16 strains of dermatophytes investigated utilized cystine (added to the gelatin medium) as a Rource of sulfur and also of carbon and nitrogen. Excess sulfur was oxidized and excreted to the medium, primarily as inorganic sulfate. Six strains used up all eystine and excreted more than 90% stoichiometrie amount of sulfur. Cystine utilization proceeded in parallel with the development of the culture and was terminated during the stationary phase or as late as in the autolytie phase. Other strains did not use up cystine eompletely and excreted 17–70% sulfur in the oxidized form. In addition to sulfate, sulfite was always produced during the initial growth phases and in poorly growing strains. Free sulfite was only rarely detected; it usually reacted with the residual cystine yielding S-sulfocysteine that was also used up later. Specific features of cystine metabolism (known fromMicrosporum gypseum) are generally valid in dermatophytes.