EDB Gene Cluster-Dependent Indole Production Is Responsible for the Ability of Pseudomonas fluorescens NZI7 to Repel Grazing by Caenorhabditis elegans .

The "EDB" (from "edible") gene cluster, a variant of the ebo cluster of genes found in many bacteria and algae, allows Pseudomonas fluorescens NZI7 (referred to here as "NZI7") to repel grazing by the nematode Caenorhabditis elegans . The mechanism underlying this phenotype is unknown. Here we report that the EDB cluster is involved in the conversion of tryptophan to (1 H -indol-3-yl)-oxoacetamide, indole 3-aldehyde, and other indole-derived compounds. Inactivation of the EDB genes in NZI7 resulted in mutants that lack the ability to excrete indole-derived compounds as well as the ability to repel C. elegans . Heterologous expression of the NZI7 EDB cluster in E. coli cultivated in minimal M9 medium containing 2 mM l-tryptophan also released indole derivatives including tryptophol, 3-(hydroxyacetyl)indole, colletotryptin E, and two new dimeric indoles. Expression of the NZI7 EDB cluster in E. coli , cultured in minimal M9 medium and lacking tryptophan, did not produce detectable levels of indole derivatives. Both (1 H -indol-3-yl)-oxoacetamide and indole 3-aldehyde showed repellent activity against C. elegans , revealing the mechanism underlying the ability of P. fluorescens NZI7 to repel grazing by C. elegans .