Nitrogen availability and production of bikaverin and gibberellins in Gibberella fujikuroi

Production of bikaverin and gibberellins by Gibberella fujikuroi started af ter depletion of the nitrogen source, but not after depletion of phosphate. Despite this similarity, the regulation of both pathways by nitrogen invol ved two different mechanisms. This conclusion was supported by the fact tha t the production of bikaverin, in contrast to the gibberellins, was not inh ibited by nitrate in a mutant that could not utilize it. The different regu lation of both pathways was clearly demonstrated by a mutant that overprodu ced bikaverin but lacked gibberellins. An optimal bikaverin production requ ired a low pH, with a sharp drop at about pH 5. The syntheses of fungal sec ondary metabolites, such as bikaverin and gibberellins, are not subject to common regulation, but respond to various combinations of signals, such as nitrogen availability, nitrate and the pH of the medium. (C) 1999 Federatio n of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.