Abbau und Assimilation von Glukose und Aminosäuren durch Microsporum gypseum: Degradation and Assimilation of Glucose and Amino Acids by Microsporum gypseum

Utilization of cystine by dermatophytes on glucose-peptone media

All the 16 strains of dermatophytes tested here metabolized cystine (3 mmol/L) in two glucose-peptone media with a different C: N ratio. Cystine was utilized as a sulfur source and, in addition, as a carbon and nitrogen source, in parallel with growth. Excess sulfur was excreted to the medium after its oxidation as inorganic sulfate and sulfite. In a physiologically alkaline medium the growth was fast and was accompanied by a pH increase and cystine was utilized intensively. Eleven species used up all cystine available. Sulfate was the main oxidation product, sulfite was produced at a low concentration, at the beginning of growth in particular. Only traces of thiol compounds (cysteine) were present in the medium. In a physiologically acid medium growth was soon limited by a decreased pH (below 5.0) but cystine continued to be utilized at an identical rate. All cystine was used up by 5 species. The tendency to produce sulfite in addition to sulfate further increased and sulfite was often the predominant product. Concentrations of thiol compounds were also substantially higher. Thus, dermatophytes can utilize cystine even under conditions that do not support good growth and increase the sulfite production.

Utilization of cystine by dermatophytes on a gelatin medium

All 16 strains of dermatophytes investigated utilized cystine (added to the gelatin medium) as a source of sulfur and also of carbon and nitrogen. Excess sulfur oxidized and excreted to the medium, primarily as inorganic sulfate. Six strains used up all cystine and excreted more than 90% stoichiometric 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 autolytic phase. Other strains did not use up cystine completely 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 from Microsporum gypseum) are generally valid in dermatophytes.

Utilization of various concentrations of free cystine by the fungus Microsporum gypseum

The dermatophyte Microsporum gypseum was cultivated on two liquid media enriched with 50 to 1000 micrograms/ml free L-cystine. The presence of cystine in concentrations above 250 micrograms/ml (gelatin medium) or 500 micrograms/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 micrograms/ml but decreased again with 1000 micrograms/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.

Cystine catabolism in mycelia of Microsporum gypseum, a dermatophytic fungus

The fate of 35S label was studied during cystine degradation by mycelia of the dermatophytic fungus Microsporum gypseum. Excess free cystine in the medium was readily taken up and its sulfur moiety excreted as inorganic sulfate and sulfite. At intervals after 3-60 min of incubation with 35S cystine the products of cystine catabolism were extracted from the mycelia by boiling water and separated by thin layer chromatography and electrophoresis. A total of 10 sulfur-containing compounds were identified, and their relative radioactivity was assessed. After 3 min the mycelia contained, in addition to cystine, labeled cysteine and particularly cysteine sulfinic acid which was accompanied by a smaller amount of cysteic acid. Later on, oxidized and reduced glutathione, inorganic sulfate and taurine appeared consecutively. In all extracts, small amounts of labeled S-sulfocysteine were found, not, however, sulfite. The results suggest that the intermediates of cysteine degradation in the fungal mycelia are cysteine, cysteine sulfinate, unstable sulfinylpyruvate, sulfite and sulfate, i.e., that the catabolic pattern is similar to that of higher organisms. The formation and the role of S-sulfocysteine, cysteic acid, and of taurine is not yet completely understood, although certainly autoxidative processes are involved in the formation of the latter two compounds, and sulfitolysis in that of the former compound.

Metabolism of sulfur-containing amino acids in the dermatophyte Microsporum gypseum. I. Neutral amino acids

The dermatophyte Microsporum gypseum was cultivated on a glucose-arginine medium to which on out of six sulfur-containing amino acids was added (L-cystine, L-djenkolic acid, DL-lanthionine DL-homocystine, L-methionine, or L-methionine-sulfone at a concentration of 5 mM with respect to sulfur content). The addition of these substances did not stimulate the growth and some amino acids (djenkolic acid and particularly methionine and methionine-sulfone) were inhibitory. All tested compounds were utilized during the growth not only as sulfur source but as a source of carbon and nitrogen as well. In four substrates excess sulfur was excreted after oxidation into the medium in the form of sulfate. Small amounts of sulfite were also observed. It usually reacted with remaining disulfides in the medium forming S-sulfo compounds (R-S.SO3H). Cystine and djenkolic acid were oxidized rapidly and completely. In contrast, lanthionine and particularly homocystine were oxidized slowly and only after a longer adaptation. To some extent lanthionine was already oxidized extracellularly in the medium. With methionine and its sulfone, excess sulfur was not removed by oxidation but by demethiolation to methane thiol and further volatile products.