Dual-purpose isocyanides produced by <i>Aspergillus fumigatus</i> contribute to cellular copper sufficiency and exhibit antimicrobial activity.

Abstract

The maintenance of sufficient but nontoxic pools of metal micronutrients is accomplished through diverse homeostasis mechanisms in fungi. Siderophores play a well established role for iron homeostasis; however, no copper-binding analogs have been found in fungi. Here we demonstrate that, in <i>Aspergillus fumigatus</i>, xanthocillin and other isocyanides derived from the <i>xan</i> biosynthetic gene cluster (BGC) bind copper, impact cellular copper content, and have significant metal-dependent antimicrobial properties. <i>xan</i> BGC-derived isocyanides are secreted and bind copper as visualized by a chrome azurol S (CAS) assay, and inductively coupled plasma mass spectrometry analysis of <i>A. fumigatus</i> intracellular copper pools demonstrated a role for <i>xan</i> cluster metabolites in the accumulation of copper. <i>A. fumigatus</i> coculture with a variety of human pathogenic fungi and bacteria established copper-dependent antimicrobial properties of <i>xan</i> BGC metabolites, including inhibition of laccase activity. Remediation of xanthocillin-treated <i>Pseudomonas aeruginosa</i> growth by copper supported the copper-chelating properties of <i>xan</i> BGC isocyanide products. The existence of the <i>xan</i> BGC in several filamentous fungi suggests a heretofore unknown role of eukaryotic natural products in copper homeostasis and mediation of interactions with competing microbes.