Abstract
Penicillium rubrum Stoll, a toxigenic mould, was first implicated in a mycotoxicosis in 1956 when it was suspected to be one of the causal agents of swine poisoning. Since then a number of studies have been performed on the toxins elaborated by this organism and on the effects of the external environment on their synthesis. The present study was performed using the CMI 112715 strain of this mould and several nutritional factors have been examined. A chemically defined medium has been developed during the course of this study which gave rise to toxin yields comparable with those of the enriched Raulin-Thom medium. Of special interest were the effects of carbon and nitrogen content of the medium on toxin synthesis and some interesting results have been obtained through the use of metabolic inhibitors such as malonate and ferrocyanide. The secondary metabolic nature of the toxins has been established and attempts have been made to establish the relative importance of the various primary metabolic pathways in generating the intermediates required in rubratoxin synthesis, by use of the above mentioned inhibitors. This study confirmed the importance of the C/N ratio in secondary metabolic activity of fungi and in the case of rubratoxin synthesis indicated a possible indirect effect of absence of zinc on toxin synthesis. Effects of some other nutritional factors are discussed in connection with the biosynthesis of rubratoxins by this mould.