Two-component transcriptional regulation of N-acyl-homoserine lactone production in Pseudomonas aureofaciens

Production of phenazine antibiotics by the biological control bacterium Pse udomonas aureofaciens 30-84 is regulated in part by the PhzI/PhzR N-acyl-ho moserine lactone (AHL) response system (L. S. Pierson III,V. D. Keppenne, a nd D. W. Wood, J Bacteriol. 176:3966-3974, 1994; D. W. Wood and.. Pierson H i, Gene 168:49-53, 1996). Two mutants, 30-84W and 30-84.A2, were isolated a nd were found to be deficient in the production of phenazine, protease, hyd rogen cyanide (HCN), and the AHL signal N-hexanoyl-homoserine lactone. Thes e mutants were not complemented by phzI, phzR, or the phenazine biosyntheti c genes (phzFABCD) (L. S. Pierson III, T. Gaffney, S. Lam, and F. Gong, FEM S Microbiol. Lett. 134:299-307, 1995). A 2.2-kb region of the 30-84 chromos ome which fully restored production of all of these compounds in strain 30- 84W was identified, Nucleotide sequence analysis of this region revealed a single open reading frame encoding a predicted 213-amino-acid protein which is very similar to the global response regulator GacA. Strain 30-84.A2 was not complemented by gacA or any cosmid from a genomic library of strain 30 -84 but was complemented by gacS (formerly lemA) homologs from Pseudomonas fluorescens Pf-5 (N. Corbel and J. E. Loper, J. Bacteriol. 177:6230-6236, 1 995) and Pseudomonas syringae pv. syringae B728a (E. M. Hrabek and D. K. Wi llis, J. Bacteriol. 174:3011-3020,1992). Transcription of phzR was not alte red in either mutant; however, phzI transcription was eliminated in strains 30-84W and 30-84.A2. These results indicated that the GacS/GacA two-compon ent signal transduction system of P. aureofaciens 30-84 controls the produc tion of AHL required for phenazine production by mediating the transcriptio n of phzI; Addition of exogenous AHL did not complement either mutant for p henazine production, indicating that the GacS/GacA global regulatory system controls phenazine production at multiple levels. Our results reveal for t he first time-a mechanism by which a two-component regulatory system and an AHL-mediated regulatory system interact.