The phzI gene of Pseudomonas aureofaciens 30-84 is responsible for the production of a diffusible signal required for phenazine antibiotic production.

The production of phenazine (Ph) antibiotics in Pseudomonas aureofaciens (Pau) 30-84 is positively regulated by PhzR, a protein belonging to the LuxR family of transcriptional activators. We have now identified phzI, a second gene required for PH production. The product of phzI is a member of the LuxI family of N-acyl-homoserine lactone (N-acyl-HSL) synthases. Inactivation of phzI results in the loss of Ph production in Pau 30-84. The presence of phzI in Escherichia coli is sufficient for the production of a diffusible signal which activates phzB expression in Pau 30-84 and traA expression in a N-acyl-HSL-dependent reporter strain of Agrobacterium tumefaciens. In addition, synthetic N-(3-oxohexanoyl)-L-HSL induces phzB expression in Pau 30-84. These results suggest that Pau 30-84 produces a N-acyl-HSL signal that regulates Ph production, and that phzI plays a central role in this signaling pathway.