Providencia stuartii genes activated by cell-to-cell signaling and identification of a gene required for production or activity of an extracellular factor

By utilizing reporter transposons, five Providencia stuartii genes that are activated by the accumulation of self-produced extracellular signals have been identified. These genes have been designated cma for conditioned mediu m activated. The presence of conditioned medium from stationary-phase cultu res grown in rich media resulted in the premature activation of each gene i n cells at early log phase, with activation values ranging from 6- to 26-fo ld. Preparation of conditioned medium from an M9 salts medium and fractiona tion by gel filtration chromatography resulted in fractions within the incl uded volume which activated three of the cma fusions. In addition, dependin g on the reporter fusion, peak activity was found in different fractions. T he partially purified factors activated in a dose-dependent manner. Charact erization of the factors activating the cma fusions indicated that they wer e stable to heat, alkali, and acid. Furthermore, for each cma fusion, facto r activity,vas not reproduced by the addition of homoserine lactone, homocy steine thiolactone, pyruvate, Casamino Acids, or a-ketoglutarate. The ident ities of three cma genes have been determined and revealed physiological ro les in amino acid biosynthesis and nutrient import. To begin to address the pathways for production of or response to the extracellular factors, we ha ve identified a locus, aarA, that is required for the activation of four cm a fusions. The AarA product was required for factor activity in extracellul ar supernatants, indicating a possible role in biosynthesis or export.