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Appl Environ Microbiol. 1992 July; 58(7): 2308-2314
Copyright © 1992, American Society for Microbiology. All Rights Reserved.

Utilization of Carbon Substrates, Electrophoretic Enzyme Patterns, and Symbiotic Performance of Plasmid-Cured Clover Rhizobia

J. Ivo Baldani{dagger}, R. W. Weaver*, M. F. Hynes and B. D. Eardly

1 Department of Soil & Crop Sciences, Texas A&M University, College Station, Texas 77843; Department of Biological Sciences, University of Calgary, Calgary, Canada T2N 1N42; and Pennsylvania State University, Berks Campus, Reading, Pennsylvania 196103

ABSTRACT

Plasmids in Rhizobium spp. are relatively large, numerous, and difficult to cure. Except for the symbiotic plasmid, little is known about their functions. The primary objective of our investigation was to obtain plasmid-cured derivatives of Rhizobium leguminosarum bv. trifolii by using a direct selection system and to determine changes in the phenotype of the cured strains. Three strains of rhizobia were utilized that contained three, four, and five plasmids. Phenotypic effects observed after curing of plasmids indicated that the plasmids were involved in the utilization of adonitol, arabinose, catechol, glycerol, inositol, lactose, malate, rhamnose, and sorbitol and also influenced motility, lipopolysaccharide production, and utilization of nitrate. Specific staining of 26 enzymes electrophoretically separated on starch gels indicated that superoxide dismutase, hexokinase, and carbamate kinase activities were affected by curing of plasmids. Curing of cryptic plasmids also influenced nodulation and growth of plants on nitrogen-deficient media. The alteration in the ability to utilize various substrates after curing of plasmids suggests that the plasmids may encode genes that contribute significantly to the saprophytic competence of rhizobia in soil.


FOOTNOTES

* Corresponding author.

{dagger} Permanent address: Embrapa-Km 47 UAPNPBS, Seropedica, 23851 Rio de Janeiro, Brazil.


Appl Environ Microbiol. 1992 July; 58(7): 2308-2314
Copyright © 1992, American Society for Microbiology. All Rights Reserved.




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Copyright © 1992 by the American Society for Microbiology. All rights reserved.