title: Identification of an rsh gene from a Novosphingobium sp. necessary for quorum-sensing signal accumulation.
abstract: 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 (rsh(Nsp)) 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 rsh(Nsp) gene restored these phenotypes. This is the first discovery of a functional rsh gene in a member of the Novosphingobium genus.
authors.affiliation: Department of Biological Sciences, Rochester Institute of Technology, 85 Lomb Memorial Dr., A350 Gosnell Bldg., Rochester, NY 14534, USA. massbi@rit.edu
authors.forename: Han Ming
authors.initials: HM
authors.lastname: Gan
authors.forename: Larry
authors.initials: L
authors.lastname: Buckley
authors.forename: Erno
authors.initials: E
authors.lastname: Szegedi
authors.forename: André O
authors.initials: AO
authors.lastname: Hudson
authors.forename: Michael A
authors.initials: MA
authors.lastname: Savka
mesh_terms: D054742:Acyl-Butyrolactones / Q000378:metabolism*; D000595:Amino Acid Sequence; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D020459:Genes, rRNA; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010802:Phylogeny; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D053038:Quorum Sensing; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D042301:Sphingomonadaceae / Q000145:classification / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D027843:Vitis / Q000382:microbiology
chemical_list: D054742:Acyl-Butyrolactones; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D011135:Polysaccharides, Bacterial; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S