Biosynthesis of the antifungal compound fragin is controlled by a novel quorum sensing signal

Members of the diazeniumdiolate class of natural compounds show great potential for drug development. Yet, their biosynthesis has remained elusive to date. Here, we identify a gene cluster directing the biosynthesis of the diazeniumdiolate compound fragin in Burkholderia cenocepacia H111. We provide evidence that fragin is a metallophore and that metal chelation is the molecular basis of its antifungal activity. We also show that a subset of the fragin biosynthetic genes is involved in the synthesis of a novel cell-to-cell signaling molecule, valdiazen. RNA-Seq analyses revealed that valdiazen not only controls fragin biosynthesis but affects expression of more than 100 genes. Homologs of the valdiazen biosynthesis genes are found in various bacteria, suggesting that valdiazen is the first representative of a new signal molecule class. Using structural information, in silico prediction of enzymatic functions and biochemical data we propose a biosynthesis route for fragin and valdiazen. Triple RNA-seq datasets of B. cenocepacia H111 wild type compared with a mutant strain and the chemical complementation of the mutant strain.