Tenellin acts as an iron chelator to prevent iron-generated reactive oxygen species toxicity in the entomopathogenic fungus Beauveria bassiana

Iron is an essential element for life. However, the iron overload can be toxic. Here, we investigated the significant increase of tenellin and iron-tenellin complex production in ferricrocin-deficient mutants of Beauveria bassiana. Our chemical analysis indicated that the ferricrocin-deficient mutants T1, T3 and T5 nearly abolished ferricrocin production. In turn, these mutants had significant accumulation of iron-tenellin complex in their mycelia at 247-289 mg g(-1) cell dry weight under iron-replete condition. Both tenellin and iron-tenellin complex were not detected in the wild-type under such condition. Mass analysis of the mutants' crude extracts demonstrated that tenellin formed a 3:1 complex with iron in the absence of ferricrocin. The unexpected link between ferricrocin and tenellin biosynthesis in ferricrocin-deficient mutants could be a survival strategy during iron-mediated oxidative stress.