Stimulation of bikaverin production by sucrose and by salt starvation in Fusarium fujikuroi

The fungus Fusarium fujikuroi (Gibberella fujikuroi mating group C) exhibits a rich secondary metabolism that includes the synthesis of compounds of biotechnological interest, such as gibberellins, bikaverin, and carotenoids. The effect of the carbon source on their production was checked using a two-phase incubation protocol, in which nine different sugars were added upon transfer of the fungus from repressed to appropriate inducing conditions, i.e., nitrogen starvation for gibberellins and bikaverin and illumination for carotenoids production. Most of the carbon sources allowed the synthesis of these metabolites in significant amounts. However, bikaverin production was strongly increased by the presence of sucrose in comparison to other carbon sources, an effect not exhibited for the production of gibberellins and carotenoids. The bikaverin inducing effect was enhanced in the absence of phosphate and/or sulfate. Similar results were also observed in carotenoid-overproducing strains known to be altered in bikaverin production. The induction by salt starvation, but not by sucrose, correlated with an increase in messenger RNA levels of gene bik1, encoding a polyketide synthase of the bikaverin pathway.