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Journal of Bacteriology, April 2009, p. 2551-2560, Vol. 191, No. 8
0021-9193/09/$08.00+0     doi:10.1128/JB.01692-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Identification of an rsh Gene from a Novosphingobium sp. Necessary for Quorum-Sensing Signal Accumulation{triangledown} ,{dagger}

Han Ming Gan,1 Larry Buckley,1 Erno Szegedi,2 André O. Hudson,1 and Michael A. Savka1*

Department of Biological Sciences, Rochester Institute of Technology Rochester, New York 14623,1 Research Institute for Viticulture and Enology, P.O. Box 25, H-6001 Kecskemét, Hungary2

Received 4 December 2008/ Accepted 29 January 2009

The stringent response is a mechanism by which bacteria adapt to environmental stresses and nutritional deficiencies through the synthesis and hydrolysis of (p)ppGpp by RelA/SpoT enzymes. Alphaproteobacteria and plants contain a single Rsh enzyme (named for RelA/SpoT homolog) that is bifunctional. Here we report the identification of a new species of bacteria belonging to the genus Novosphingobium and characterization of an rsh mutation in this plant tumor-associated isolate. Isolate Rr 2-17, from a grapevine crown gall tumor, is a member of the Novosphingobium genus that produces the N-acyl-homoserine lactone (AHL) quorum-sensing (QS) signals. A Tn5 mutant, Hx 699, deficient in AHL production was found to have an insertion in an rsh gene. The Rsh protein showed significant percent sequence identity to Rsh proteins of alphaproteobacteria. The Novosphingobium sp. rsh gene (rshNsp) complemented the multiple amino acid requirements of the Escherichia coli relA spoT double mutant by restoring the growth on selection media. Besides QS signal production, the rsh mutation also affects soluble polysaccharide production and cell aggregation. Genetic complementation of the Hx 699 mutant with the rshNsp gene restored these phenotypes. This is the first discovery of a functional rsh gene in a member of the Novosphingobium genus.

* Corresponding author. Mailing address: Department of Biological Sciences, Rochester Institute of Technology, 85 Lomb Memorial Dr., A350 Gosnell Bldg., Rochester, NY 14534. Phone: (585) 475-5141. Fax: (585) 475-5760. E-mail: massbi{at}rit.edu

{triangledown} Published ahead of print on 6 February 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, April 2009, p. 2551-2560, Vol. 191, No. 8
0021-9193/09/$08.00+0     doi:10.1128/JB.01692-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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