Journal of Bacteriology, December 1999, p. 7185-7191, Vol. 181, No. 23
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Departments of Medicine and Molecular Biology
and Microbiology,
Received 25 August 1999/Accepted 15 September 1999
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 medium activated.
The presence of conditioned medium from stationary-phase cultures grown
in rich media resulted in the premature activation of each gene in cells at early log phase, with activation values ranging from 6- to
26-fold. Preparation of conditioned medium from an M9 salts medium and
fractionation by gel filtration chromatography resulted in fractions
within the included volume which activated three of the cma
fusions. In addition, depending on the reporter fusion, peak activity
was found in different fractions. The partially purified factors
activated in a dose-dependent manner. Characterization of the factors
activating the cma fusions indicated that they were stable
to heat, alkali, and acid. Furthermore, for each cma fusion, factor activity was not reproduced by the addition of homoserine lactone, homocysteine thiolactone, pyruvate, Casamino Acids,
or
-ketoglutarate. The identities of three cma genes
have been determined and revealed physiological roles in amino acid biosynthesis and nutrient import. To begin to address the pathways for
production of or response to the extracellular factors, we have
identified a locus, aarA, that is required for the
activation of four cma fusions. The AarA product was
required for factor activity in extracellular supernatants, indicating
a possible role in biosynthesis or export.
*
Corresponding author. Mailing address: Division of
Infectious Diseases, BRB-10, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106. Phone: (216) 368-0733. Fax: (216) 368-2034. E-mail:
pxr17{at}po.cwru.edu.
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