Rare Gene Cluster for Desferriferrichrome Biosynthesis Controls the Conflict between Trap Formation and Nematicidal Activity in .

The formation of the trapping device induced by nematodes has been assumed as an indicator for a switch from saprophytic to predacious lifestyles for nematode-trapping fungi. However, fungal nematocidal activity is not completely synonymous with fungal trap formation. We found that the predominant nematode-trapping fungus harbored a rare () gene cluster that was mainly distributed in nematode-trapping fungi. The gene putatively encodes a protein with a unique domain organization, distinct from other NRPSs in other fungi. Mutation of the two key biosynthetic genes and combined with nontarget metabolic analysis revealed that the gene cluster was responsible for the biosynthesis of a hydroxamate siderophore, desferriferrichrome (). Lack of desferriferrichrome () and its hydroxamate precursor () could lead to significantly increased Fe content, which induced fungal trap formation without a nematode inducer. Furthermore, the addition of Fe strongly improved fungal trap formation but deleteriously caused broken traps. The addition of significantly attenuated trap formation but enhanced fungal nematicidal activity. Our findings indicate that iron is a key factor for trap formation and provide a new insight into the underlying mechanism of siderophores in nematode-trapping fungi.