Rhizobium etli
A Microbial Biorealm page on the genus Rhizobium etli
Classification
Higher order taxa
Bacteria (Domain); Proteobacteria (Phylum); Alphaproteobacteria (Class); Rhizobiales (Order); Rhizobiaceae (family)
Species
Rhizobium Etli
Description and significance
Rhizobium Etli is one of the many soil-living bacteria able to live in conditions of nitrogen limitation due to its distinctive ability to settle onto root nodules of legumes. Like other rhizobia, it is characterized as aerobic,gram negative and able to form symbiotic relationship with legumes. (1, 2) In specific, rhizobium etli is the predominant bacteria found legumes such as the common bean, P. Vulgaris. (3)
Rhizobium Etli is found world wide and discovered as early as 16th century. Due to its early existence, attempts to identify origin of the species was performed by identifying its molecular marker. This was performed by searching a diversity within different rhizobium etli species from P. Vulgaris. Isolation of the rhizobia strain from the nodule of the root of the plant was removed, sterilized with ethanol and hydrogen peroxides, and grown on YEM-Congo red agar medium. Isolation and identification was done by 16S rRNA-encoding DNA-RFLP analysis. The analysis showed most to be from species rhizobium etli. The nodC gene was identified and isolated to be used as a molecular marker. Results from the experiment showed rhizobium etli is not only found in the America’s but also identified in parts of Africa, Asia, and Europe. (3)
Rhizobium Etli is important enough to have its genome sequence because of its unique ability to form symbiotic relationship with legumes. The detail in which it performs this will be in the cell structure and metabolism section. To give a general idea of its importance, the host benefits by being provided nitrogen in the form of ammonia from the bacteria, while the bacteria is provided carbon and nutrients from the host. (2)
In agriculture, crop rotation and soil fumigation is performed each year to prevent diseases. Futher knowledge of the bacteria would allow possible genetic engineering onto the bacteria to possibly work as an antibiotic. (4)
Genome structure
Rhizobium Etli has a complete genome sequence of 6,530,228 base pairs. It contains 4,381,608 circular chromosomes averaging 61.27% GC content. (5)
Six plasmids: p42a, p42b, p42c, p42d, p42e, and p42f, contain the complete metabolic pathways. The p42a and p42d plasmids is abnormal as it contains a lower GC value of 58% as compared to the other four plasmids at 61.5%. Also, the complete genome sequence reveals identical of more then 100 nucleotide repeats which are located in plasmid p42a and p42d. The plasmids appear to have been acquired at some point of divergence which is unknown. (5)
Its plasmids also contain Rep ABC replicator which allows stability with distinct initiators and origins of replication. An advantage to the separation of genomes is faster duplication to replicate its genome. (5)
In addition, rhizobium etli contains the most abundant number of replicons when comparing to other known nitrogen-fixing bacteria. Its protein-coding genes are classified as COGs, and are indicated to be overrepresented. Carbohydrate transport and metabolism, amino acid metabolism and transcription are several of the COGs overrepresented. (5)
As for its transcriptional regulation, 23 sigma factors are found. Though most of the roles are unknown, they are thought to required for gene expression under the different environmental conditions faced. (5) 536 transcriptional factors are found, and 331 which are one-component regulators. The majority (65%) of the one component regulators are near ABC transporters or permease genes which may activate in response to the environmental stress in the soil.(5)
The unique genomic structure, special feature of the plasmids, and overrepresentation of certain COGs and transcription regulation contribute to the genomic plasticity. All of the factors mentioned, contribute and are vital for its symbiotic lifestyle in the soil. (5)
Cell structure and metabolism
Describe any interesting features and/or cell structures; how it gains energy; what important molecules it produces.
Ecology
Describe any interactions with other organisms (included eukaryotes), contributions to the environment, effect on environment, etc.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
Does this organism produce any useful compounds or enzymes? What are they and how are they used?
Current Research
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References
Edited by student of Rachel Larsen
