Rhizobium meliloti mutants that overproduce the R. meliloti acidic Calcofluor-binding exopolysaccharide

Journal Article · Thu Sep 01 00:00:00 EDT 1988 · Journal of Bacteriology; (USA)

OSTI ID:7068014

Doherty, D; Glazebrook, J; Walker, G C ^[1]; Leigh, J A ^[2]

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1. Massachusetts Institute of Technology, Cambridge (USA)
2. Univ. of Washington, Seattle (USA)

The acidic Calcofluor-binding exopolysaccharide of Rhizobium meliloti Rm1021 plays one or more critical roles in nodule invasion and possible in nodule development. Two loci, exoR and exoS, that effect the regulation of synthesis of this exopolysaccharide were identified by screening for derivatives of strain Rm1021 that formed mucoid colonies that fluoresced extremely brightly under UV light when grown on medium containing Calcofluor. The exopolysaccharide produced in large quantities by the exoR95::Tn5 and exoS96::Tn5 strains was indistinguishable from that produced by the parental strain Rm1021, and its synthesis required the function of at least the exoA, exoB, and exoF genes. Both the exoR and exoS loci were located on the chromosome, and the exo96::Tn5 mutation was 84% linked to the trp-33 mutation by {Phi}M12 transduction. Synthesis of the Calcofluor-binding exopolysaccharide by strain Rm1021 was greatly stimulated by starvation for ammonia. In contrast, the exoR95::Tn5 mutant produced high levels of exopolysaccharide regardless of the presence or absence of ammonia in the medium. The exoS96::Tn5 mutant produced elevated amounts of exopolysaccharide in the presence of ammonia, but higher amounts were observed after starvation for ammonia. The presence of either mutation increased the level of expression of exoF::TnphoA and exoP::TnphoA fusions. Analyses of results obtained when alfalfa seedlings were inoculated with the exoR95::Tn5 strain indicated that the mutant strain could not invade nodules. However, pseudorevertants that retained the original exoR95::Tn5 mutant but acquired unlinked suppressors so that they produced an approximately normal amount of exopolysaccharide were able to invade nodules and fix nitrogen.

• DOE Contract Number: FG06-86ER13532
• OSTI ID: 7068014
• Journal Information: Journal of Bacteriology; (USA), Vol. 170:9; ISSN 0021-9193
• Country of Publication: United States
• Language: English

Related Subjects

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ALFALFA
NITROGEN FIXATION
BACTERIA
GENE REGULATION
MUTATIONS
RADIOINDUCTION
POLYSACCHARIDES
BIOSYNTHESIS
FLUORESCENCE
GENES
ULTRAVIOLET RADIATION
CARBOHYDRATES
ELECTROMAGNETIC RADIATION
LEGUMINOSAE
LUMINESCENCE
MAGNOLIOPHYTA
MAGNOLIOPSIDA
MICROORGANISMS
ORGANIC COMPOUNDS
PLANTS
RADIATIONS
SACCHARIDES
SYNTHESIS
560130* - Radiation Effects on Microorganisms