Utilization of various concentrations of free cystine by the fungusMicrosporum gypseum

Publisher Website
Google Scholar
Abstract
The dermatophyte Microsporum gypseum was cultivated on two liquid media enriched with 50 to 1000 μg/ml free L-cystine. The presence of cystine in concentrations above 250 μg/ml (gelatin medium) or 500 μg/ml (glucose-glutamate medium) inhibited the growth. In all variants, however, cystine was utilized from the very beginning of growth and exhausted completely until stationary phase. The rate of cystine metabolization grew with its concentration to 500 μg/ml but decreased again with 1000 μg/ml. The excess sulfur was oxidized and excreted back into the medium mainly as inorganic sulfate. Moreover, sulfite was also produced which immediately reacted with the residual cystine in the medium giving rise to S-sulfocysteine. Sulfite excretion was higher in the initial phases of growth and on the medium with poorer growth (gelatin medium). The sulfate-to-sulfite ratio was different on the two media used but was little influenced by cystine concentration. The excretion of strongly acidic compounds (sulfate, sulfite, and S-sulfocysteine) reduced the usual alkalinization of the medium in the course of growth.