Versicolin

Antibiotically active producer mutants derived from the spontaneous degenerate parent Aspergillus versicolor N5 possessed not only mutual but also self-sensitive activity. The producer mutants, like the inactive parent, were only 3.5-fold less sensitive than the most sensitive unrelated organism, Trichophyton rubrum. The germination of spores is generally more sensitive than growth of vegetative cells. The antifungal spectrum of these mutual and self-sensitive mutants was fairly wide, unlike the host range specificity of bacteriocinogenic strains acting on organisms closely related to the producers. The self and mutual growth inhibitory principle was finally identified as the antibiotics mycoversilin and versilin in the case of producer mutants (N5)17 and N5T10(7), respectively, or Vx, an antibiotic of unknown molecular species, in the case of another producer mutant N5T10(8). Thus self-sensitivity, instead of self-resistance, of these antibiotically active mutant derivatives is a unique property among filamentous fungi in having simultaneously expressed two loci of contradictory functions, one for synthesis of, and the other for sensitivity towards, the same or related antibiotics.

Soil supports the growth of a jute pathogen Colletotrichum gloeosporioides but only to a limited extent that of its antagonist Aspergillus versicolor. The growth of the sensitive pathogen is considerably checked by the antagonist in mixed soil culture although versicolin production could not be demonstrated within the limits of assay. Both the sensitive and the antagonistic organisms grow well in soil-compost medium and versicolin production by the latter is also enhanced. The antagonistic effect of Aspergillus versicolor on Colletotrichum gloeosporioides is expectedly more marked in soil-compost medium than in soil medium.

Versicolin is mainly active against Trichophyton rubrum. It is inactivated by serum. However, attainable blood level can be fifteen to twenty times higher than the fungicidal concentration for as long as 4 hours after a single intravenous administration of the maximum tolerable dose of 25 mg/kg body weight of mouse. It has no haemolytic activity like other polypeptide antibiotics. Skin does not show the presence of any measurable amount of the antibiotic. It is excreted through urine to the extent of 65% of the maximum tolerable dose of the antibiotic administered intravenously. Versicolin is effective against experimental infection by T. rubrum in guinea pigs at dose as low as 2.5 mg/kg body weight. The antibiotic shows no sign of subacute toxicity at these curative doses.