INTERPOPULATION SIGNALING VIA N-ACYL-HOMOSERINE LACTONES AMONG BACTERIA IN THE WHEAT RHIZOSPHERE

The biological control bacterium Pseudomonas aureofaciens 30-84 utiliz es an N-acyl-homoserine lactone (AHL) signal molecule to control phena zine antibiotic production in the wheat rhizosphere (D. W. Wood and L. S. Pierson III, Gene 168:49-53, 1996), In this study, we demonstrate that naturally co-existing, non-isogenic bacterial populations interac t with strain 30-84 at the level of gene expression via the exchange o f diffusible signals on wheat roots. Wheat plants from three geographi c locations were used to generate a random library of 700 rhizobacteri al isolates. Roughly 8% of the isolates from each location restored ph enazine gene expression to an AHL-deficient strain of 30-84 in vitro. Five of these isolates were further tested for their ability to influe nce gene expression of an AHL-deficient reporter of strain 30-84 on wh eat roots. All five, isolated from different geographic locations, res tored phenazine gene expression by the reporter to wild-type levels. T his suggests that in vitro assays can identify bacterial isolates with the potential to influence phenazine expression in strain 30-84 via A HLs on wheat roots. The occurrence of such strains in all fields sampl ed suggests that AHL-mediated communication is a common occurrence in the wheat rhizosphere.