title: Genetic analysis of a region of the Rhizobium meliloti pSym plasmid specifying catabolism of trigonelline, a secondary metabolite present in legumes.
abstract: Genes controlling the catabolism of trigonelline, a secondary metabolite that is often present in legumes, are located on the pSym megaplasmid of Rhizobium meliloti. To investigate the role of bacterial trigonelline catabolism in the Rhizobium-legume symbiosis, we identified and characterized the R. meliloti RCR2011 genetic loci (trc) controlling trigonelline catabolism. Tn5-B20 mutagenesis showed that the trc region is a continuous DNA segment of 9 kb located 4 kb downstream of the nifAB and fdxN genes. Trc mutants fell into two classes according to their phenotype and location: (i) mutants carrying Tn5-B20 insertions in the right-hand part of the trc region were incapable of growing on trigonelline as the sole carbon and/or nitrogen source, and (ii) insertions in the left-hand part of the trc region resulted in delayed growth on trigonelline as the sole carbon and/or nitrogen source. No significant defect in nodule formation or nitrogen fixation was detected for mutants of either class. Screening of a set of R. meliloti strains from various geographical origins showed that all of these strains are able to catabolize trigonelline and show sequence homology between their megaplasmids and a trc probe.
authors.affiliation: Laboratoire de Biologie Moléculaire des Relations Plantes-Microorganismes, Institut National de la Recherche Agronomique, Castanet-Tolosan, France.
authors.forename: C
authors.initials: C
authors.lastname: Boivin
authors.forename: L R
authors.initials: LR
authors.lastname: Barran
authors.forename: C A
authors.initials: CA
authors.lastname: Malpica
authors.forename: C
authors.initials: C
authors.lastname: Rosenberg
mesh_terms: D000470:Alkaloids / Q000378:metabolism*; D003001:Cloning, Molecular; D004251:DNA Transposable Elements; D007887:Fabaceae / Q000378:metabolism*; D005816:Genetic Complementation Test; D016254:Mutagenesis, Insertional; D010641:Phenotype; D010946:Plants, Medicinal; D010957:Plasmids; D015183:Restriction Mapping; D012231:Rhizobium / Q000235:genetics*; D013559:Symbiosis
chemical_list: D000470:Alkaloids; D004251:DNA Transposable Elements; C009560:trigonelline