The involvement of cAMP in the growth inhibition of filamentous fungus Rhizopus nigricans by steroids

Several steroids, in particular progesterone, are toxic for the filamentous fungus Rhizopus nigricans and, at high concentrations, inhibit its growth. Previous studies on this microorganism revealed progesterone specific receptors coupled to G proteins at the plasma membrane. In this study, the next step of steroid signalling in R. nigricans following G protein activation is investigated, together with the possible impact of this pathway on fungal growth inhibition. The intracellular level of cAMP decreased in the presence of steroids, demonstrating the probable involvement of cAMP signalling in the response of R. nigricans to steroids. Results of the growth analysis in the presence of cAMP increasing agents suggest that the role of cAMP in fungal growth inhibition by steroids cannot be ruled out, but it would appear to be minor and not make a major contribution to growth inhibition.