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Polypeptide synthesis by Rhizobium bacteroids and bacteria.
Biochimica Et Biophysica Acta
|June 20, 1979
Summary
Rhizobium bacteroids synthesize specific proteins, including nitrogenase components, identified using [35S]-methionine labeling. Protein patterns vary with nodule maturity and Rhizobium strain, differing from cultured bacteria.
Area of Science:
- Microbiology
- Plant-Bacterial Interactions
- Molecular Biology
Background:
- Rhizobium bacteroids are key symbionts in legume nitrogen fixation.
- Understanding bacteroid protein synthesis is crucial for optimizing symbiosis.
- Previous studies identified nitrogenase polypeptides but lacked detailed protein synthesis profiles.
Purpose of the Study:
- To characterize the de novo synthesized polypeptides in Rhizobium bacteroids.
- To investigate how environmental conditions and developmental stages affect bacteroid protein profiles.
- To compare protein synthesis patterns between bacteroids and cultured bacteria.
Main Methods:
- Isolation and aerobic incubation of Rhizobium bacteroids (strain NZP 2257) from lupin nodules.
- Incorporation of [35S]-methionine to label newly synthesized polypeptides.
- Analysis of labeled polypeptides using SDS-polyacrylamide gel electrophoresis.
- Pulse-chase experiments to assess polypeptide stability.
- In situ labeling of bacteroids within detached nodules.
Main Results:
- A distinct set of polypeptides was synthesized by isolated bacteroids, with many matching Coomassie blue-stained bands.
- Labeled polypeptides were stable for several hours.
- Ion concentrations (H+, K+, Mg2+) affected overall labeling but not relative patterns.
- Distinct labeling patterns were observed in mature vs. immature bacteroids, correlating with nitrogenase appearance.
- Two major labeled components in mature bacteroids (60 and 34 kDa) likely represent nitrogenase subunits.
- Bacteroids from the same strain but different hosts showed similar patterns; different strains showed distinct patterns.
- Bacteroid labeling patterns differed significantly from those of broth-cultured Rhizobium.
Conclusions:
- Rhizobium bacteroids exhibit specific protein synthesis profiles, distinct from cultured bacteria.
- Bacteroid polypeptide synthesis is regulated by plant developmental stage and Rhizobium strain.
- The identified labeled polypeptides, particularly the 60 and 34 kDa components, are strong candidates for nitrogenase subunits, providing insights into symbiosis regulation.