Preparation and properties of spheroplasts from Aspergillus parasiticus with special reference to the de novo synthesis of aflatoxins

Abstract

Spheroplasts were prepared from Aspergillus parasiticus NRRL 3240 using β-glucuronidase from Helix pomatia. They were osmotically fragile spherical structures which lysed when suspended in hypotonic buffers. Purity of the preparation was confirmed by phase-contrast microscopy. Maximal conversion of mycelia to spheroplasts was achieved with 48 and 72 h old cultures. Spheroplasts were metabolically active as indicated by the incorporation of labelled thymidine, uridine and leucine into DNA, RNA and proteins, respectively. A significant incorporation of [methyl-³H] thymidine into trichloroacetic acid-insoluble material suggested the presence of thymidine kinase in this organism. Spheroplasts and lysates demonstrated the ability to incorporate labelled acetate into aflatoxins. Maximum incorporation was observed in those prepared from 96 h old cultures. Lysates were more efficient in de novo aflatoxin synthesis as compared to intact mycelia and spheroplasts.