title: Sinorhizobium fredii HH103 mutants affected in capsular polysaccharide (KPS) are impaired for nodulation with soybean and Cajanus cajan.
abstract: The Sinorhizobium fredii HH103 rkp-1 region, which is involved in capsular polysaccharides (KPS) production, was isolated and sequenced. The organization of the S. fredii genes identified, rkpUAGHIJ and kpsF3, was identical to that described for S. meliloti 1021 but different from that of S. meliloti AK631. The long rkpA gene (7.5 kb) of S. fredii HH103 and S. meliloti 1021 appears as a fusion of six clustered AK631 genes, rkpABCDEF. S. fredii HH103-Rif(r) mutants affected in rkpH or rkpG were constructed. An exoA mutant unable to produce exopolysaccharide (EPS) and a double mutant exoA rkpH also were obtained. Glycine max (soybean) and Cajanus cajan (pigeon pea) plants inoculated with the rkpH, rkpG, and rkpH exoA derivatives of S. fredii HH103 showed reduced nodulation and severe symptoms of nitrogen starvation. The symbiotic capacity of the exoA mutant was not significantly altered. All these results indicate that KPS, but not EPS, is of crucial importance for the symbiotic capacity of S. fredii HH103-Rif(r). S. meliloti strains that produce only EPS or KPS are still effective with alfalfa. In S. fredii HH103, however, EPS and KPS are not equivalent, because mutants in rkp genes are symbiotically impaired regardless of whether or not EPS is produced.
authors.affiliation: Departamento de Microbiología, Facultad de Biología, Universidad de Sevilla, Av. Reina Mercedes 6. 41012-Sevilla, Spain.
authors.forename: Maribel
authors.initials: M
authors.lastname: Parada
authors.forename: José M
authors.initials: JM
authors.lastname: Vinardell
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Ollero
authors.forename: Angeles
authors.initials: A
authors.lastname: Hidalgo
authors.forename: Rocío
authors.initials: R
authors.lastname: Gutiérrez
authors.forename: Ana M
authors.initials: AM
authors.lastname: Buendía-Clavería
authors.forename: Wang
authors.initials: W
authors.lastname: Lei
authors.forename: Isabel
authors.initials: I
authors.lastname: Margaret
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: López-Baena
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Gil-Serrano
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Rodríguez-Carvajal
authors.forename: Javier
authors.initials: J
authors.lastname: Moreno
authors.forename: José E
authors.initials: JE
authors.lastname: Ruiz-Sainz
mesh_terms: D036561:Cajanus / Q000382:microbiology*; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D019906:Nuclear Magnetic Resonance, Biomolecular; D011135:Polysaccharides, Bacterial / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D042181:Sinorhizobium fredii / Q000145:classification / Q000235:genetics* / Q000502:physiology*; D013025:Glycine max / Q000166:cytology / Q000382:microbiology*
chemical_list: D011135:Polysaccharides, Bacterial