Rhizobium leguminosarum lipopolysaccharide lipid-A mutant induces nitrogen-fixing nodules with delayed and defective bacteroid formation

• Published in: Molecular plant-microbe interactions Vol. 17; no. 3; pp. 283 - 291
• Main Authors: Vedam, V, Haynes, J.G, Kannenberg, E.L, Carlson, R.W, Sherrier, D.J
• Format: Journal Article
• Language: English
• Published: St Paul, MN APS Press 01-03-2004; American Phytopathological Society; The American Phytopathological Society
• Subjects: Agronomy. Soil science and plant productions; Bacterial plant pathogens; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; bacteroid membrane; Biological and medical sciences; Economic plant physiology; Fundamental and applied biological sciences. Psychology; Hydroxy Acids - chemistry; Lipid A - chemistry; Lipid A - metabolism; lipopolysaccharides; Lipopolysaccharides - chemistry; Lipopolysaccharides - metabolism; Microscopy, Electron; mutants; Mutation; Nitrogen fixation; Nitrogen Fixation - genetics; Nitrogen Fixation - physiology; nitrogen-fixing bacteria; Nitrogenase - metabolism; nodulation; peas; Phytopathology. Animal pests. Plant and forest protection; Pisum sativum; Pisum sativum - microbiology; Plant Roots - growth & development; Plant Roots - microbiology; Plant Roots - ultrastructure; Rhizobium leguminosarum; Rhizobium leguminosarum - genetics; Rhizobium leguminosarum - growth & development; Rhizobium leguminosarum - metabolism; Rhizobium leguminosarum bv. viciae; symbionts; Symbiosis; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Microbiology; Nitrogen fixation; Lipopolysaccharide; Bacteria; Rhizobiaceae; Bacteroid; Mutation; Rhizobium leguminosarum
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/MPMI.2004.17.3.283

Lipopolysaccharides from pea-nodulating strain Rhizobium leguminosarum bv. viciae 3841, as all other members of the family Rhizobiaceae with the possible exception of Azorhizobium caulinodans, contains a very long chain fatty acid; 27-hydroxyoctacosanoic acid (27OHC28:0) in its lipid A region. The exact function and importance of this residue, however, is not known. In this work, a previously constructed mutant, Rhizobium leguminosarum bv. viciae 22, deficient in the fatty acid residue, was analyzed for its symbiotic phenotype. While the mutant was able to form nitrogen-fixing nodules, a detailed study of the timing and efficiency of nodulation using light and electron microscopy showed that there was a delay in the onset of nodulation and nodule tissue invasion. Further, microscopy showed that the mutant was unable to differentiate normally forming numerous irregularly shaped bacteroids, that the resultant mature bacteroids were unusually large, and that several bacteroids were frequently enclosed in a single symbiosome membrane, a feature not observed with parent bacteroids. In addition, the mutant nodules were delayed in the onset of nitrogenase production and showed reduced nitrogenase throughout the testing period. These results imply that the lack of 27OHC28:0 in the lipid A in mutant bacteroids results in altered membrane properties that are essential for the development of normal bacteroids.