Symbiotic mutants of Rhizobium meliloti that uncouple plant from bacterial differentiation

Cell. 1985 Apr;40(4):869-77. doi: 10.1016/0092-8674(85)90346-0.


Spontaneous mutants at a new symbiotic locus in Rhizobium meliloti SU47 are resistant to several phages and are conditionally insensitive to a monoclonal antibody to the bacterial surface, apparently because they are deficient in a wild-type exopolysaccharide. On alfalfa, the mutants do not curl root hairs, but penetrate the epidermis directly, forming nodules that contain no visible infection threads or "bacteroids," have a few bacteria in superficial intercellular spaces only and not within the nodule cells, and fail to fix nitrogen (Fix-). Evidently, infection threads are not essential for cell proliferation and nodule formation, which are here induced by a bacterial signal at a distance and uncoupled from the bacterial differentiation that normally goes on as well.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antibodies, Monoclonal / immunology
  • Bacteriophages / physiology
  • DNA Transposable Elements
  • Genes, Bacterial*
  • Medicago sativa
  • Mutation*
  • Nitrogen / metabolism
  • Plants / metabolism
  • Plants / microbiology*
  • Polysaccharides, Bacterial / genetics
  • Rhizobium / genetics*
  • Rhizobium / immunology
  • Symbiosis*


  • Antibodies, Monoclonal
  • DNA Transposable Elements
  • Polysaccharides, Bacterial
  • Nitrogen