Related Experiment Videos
DNA sequence homology in Rhizobium meliloti plasmids
Abstract:
Plasmids were recovered by an alkaline procedure from six symbiotically effective strains of Rhizobium meliloti of diverse geographical origin, reported to harbour only one middle-size large plasmid (ranging from 89 to 143 Megadaltons). Each purified plasmid was digested with eight restriction endonucleases; cleavage patterns were very complex: only KpnI and XbaI gave a limited number of bands. Fingerprints were very different, whatever the restriction enzyme or the geographical origin of the strains. However, Southern DNA-DNA hybridizations revealed that the plasmids showed homologous sequences having a high thermal stability. We gave evidence that some of these sequences are common to all the plasmids of R. meliloti. The biological function of these common sequences is unknown. Hybridization with cloned nitrogen fixation (nif) genes from Klebsiella pneumoniae had demonstrated that nif genes were not located on the middle -- size plasmids of R. meliloti studied in this paper.
Insights
Researchers studied plasmids from Rhizobium meliloti, finding unique restriction patterns but common DNA sequences. Nitrogen fixation genes were not found on these plasmids.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Plasmids are crucial genetic elements in bacteria, often carrying genes that confer adaptive advantages.
- Rhizobium meliloti plasmids are implicated in symbiosis, but their diversity and genetic content require further investigation.
- Understanding plasmid variability is key to deciphering bacterial adaptation and function.
Purpose of the Study:
- To characterize middle-size large plasmids from diverse Rhizobium meliloti strains.
- To investigate the genetic relatedness and identify conserved sequences among these plasmids.
- To determine the location of nitrogen fixation (nif) genes in relation to these plasmids.
Main Methods:
- Alkaline plasmid recovery from six Rhizobium meliloti strains.
- Restriction endonuclease digestion and gel electrophoresis for plasmid fingerprinting.
- Southern DNA-DNA hybridization to assess sequence homology.
Main Results:
- Plasmids exhibited highly complex and distinct restriction patterns across different strains and geographical origins.
- Despite unique fingerprints, Southern hybridization revealed homologous sequences with high thermal stability among plasmids.
- Common sequences were identified in all studied R. meliloti plasmids, though their function remains unknown.
- Nitrogen fixation (nif) genes were not detected on the analyzed plasmids.
Conclusions:
- Rhizobium meliloti plasmids possess both unique and conserved genetic elements.
- The conserved plasmid sequences may play a role in maintaining plasmid stability or bacterial fitness.
- The studied plasmids do not harbor the nif genes, suggesting their location elsewhere in the genome or on different plasmids.