Agrobacterium rhizogenes
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Classification
Higher order taxa
Bacteria (Domain); Proteobacteria (Phylum); Alphaproteobacteria (Class); Rhizobiales (Order); Rhizobiaceae (Family); Agrobacterium (Genus).
Species
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NCBI: [2] |
Agrobacterium rhizogenes
Description and Etymology
Agrobacterium rhizogenes is a gram negative, rod-shaped (0.6-1.0 x 1.5-3.0 µm), aerobic, soil-borne bacteria that occurs singly or in pairs and is motile by 1-4 peritrichous flagella (1). Culturing techniques require the optimal temperature for growth of 25-28C. Colony morphology will show convex, circular and smooth characteristics, while color will be non-pigmented to light beige (1). The etymological origin of the species name "rhizogenes" originates from the Greek words "rhiza" meaning a root and "gennao" to make, thus resulting in a root-producing bacteria (2).
A. rhizogenes was first isolated by Riker et al in 1930 (1) and is commonly found in the nodules of leguminous plants (3). It is known for its ability to induce tumors and hairy roots in the event of wounding or infection which produces a condition called the Hairy Root Syndrome (2). This is characterized by the overabundant growth of the plant's root system (see Figure 2). A key characteristic of the hairy root system in plants is their ability to grow quick;y in the absence of exogenous plant growth regulators (4).
The tumor induction phenotype is correlated with the presence of a large tumor inducing plasmid (Ti-plasmid), whereas the hairy root phenotype is associated with a Ri plasmid. A. rhizogenes has been a target of recent research due to its ability of using its Ri plamid, containing t-DNA, to introduce its plasmid DNA into host plants. Due to this, it has been used for a variety of purposes such as, production of plant endangered species (4), recombinant protein production and genetic engineering (3).
Genome and genetics
A. rhizogenes forms part of the bacteria domain as its characteristics define it as a alphaproteobacteria (1). Within the Agrobacterium genus, A. tumefaciens, A. rubi and A. radiobacter are closely related to it. Whole genome shotgun sequencing of the A. rhizogenes strain ATCC 15834 was performed in 2014 (5) because of its emerging importance in the areas of genetic engineering and metabolite production for medicinal purposes. The researchers who conducted the project obtained the ATCC from a hairy root culture work with tomato (3). By following the DNA extraction and sequencing protocols, the researchers obtained data that showed the length of the A. rhizogenes genome, which contains 7,070,307 bp in 43 scaffolds with a GC content of 60% (5). Automated annotation was another tool that the researchers used to confirm the species to 54 other 16 sequences and construct a phylogenic tree with the FastTree 2 software. The whole-genome shotgun project was depusited at the DDBJ/EMBL/GenBank under the accession number JFZP00000000.
Nutrition and metabolism
a.Describe the growth characteristics of your bacterial species; sources of C, N, electrons; respires/ferments, uses O2, etc.
b.What kinds of culture conditions (temp, pH, media) are needed for laboratory study?
c.What kinds of waste, by-products, volatile compounds are generated?
Hairy root disease caused by Ri plasmid bearing A. rhizogenes also involves T-DNA transfer that causes plants to produce opines, however rather than cause tumor development this disease stimulates the growth of adventitious roots (7).
Another At plasmid, pArA4, found in A. rhizogenes is a catabolic plasmid which provides the ability for its host bacteria to utilize MOP, mannopinic acid, and agropinic acid as sole sources of carbon (Guyon et al., 1993) (7).
Opine biosynthesis is catalyzed by specific enzymes encoded by genes contained in a small segment of DNA (known as the T-DNA, for 'transfer DNA'), which is part of the Ti plasmid, inserted by the bacterium into the plant genome. The opines are used by the bacterium as an important source of nitrogen and energy.
Ecology / Pathology
Ecology: How is your microorganism important in the ecosystem where it is found? How does it impact other organisms in the environment (could be positive or negative impact)?
A. rhizogenes is found in the rhizosphere of plants with as many as 10^6-10^7 cells/g soil. The impact of this bacteria within the rhizosphere is complex, as suggested by the number of populations that compete during the infection process (1). The importance of this bacterial species in the ecosystem is shown by its ability to transfer its plasmid to a host plant as the plasmid can modify the genome of the plant to express genes that aid to its survival under harsh conditions.
Pathology: How does the microbe cause disease as it interacts with the host? Describe any specific toxins or pathways that are used for invading and causing disease in the host. What treatment is used to inhibit or kill the microbe?
A. rhizogene induces the
Agrocin-producing strains have a proven role in competing with tumorigenic Agrobacterium strains to inhibit infection.
Current Research
Describe recent research and findings that have been done with this organism. The research can be clinical, applied or basic research. This section should be based on 2 recent papers (10 years or less) and summarized in your own words.
The ability that A. rhizogenes has in introducing its Ri plasmid into host plant cells has been studied for a variety of purposes. A recent study. sought to use the root-inducing phenotype of pathogenic A. rhizogenes to enhance the growth rates of endangered species such as Berberis aristata DC, commonly known as "Indian Berry" (4). The importance of endangered B. aristata lies in its medicinal applications as some of its metabolites such as benzylisoquinoline (berberin), a natural alkaloid, has shown anticancer activity as well as aiding the treatment of diabetes and malarial fever (4). The study used two different strains of A. rhizogenes (MTCC 532 and 2364) obtained from IMTECH (Institute of Microbial Technology), Chandigarh, India. In the experiment, the researchers infected the leaves of this plant in order to observe the hairy root induction and calculate the metabolite yield. Thus, the goal of the study was to device a protocol for the infection of plants with A. rhizogenes, in order to increase the production of berberin and reduce the overharvesting of this endangered species from its natural habitat (4).
References
1. Brenner, DJ., Krieg, NR., Staley, JT,. "Bergey's Manual of Systematic Bacteriology Second Edition". Vol.2. Springer. 2005. 340-345.
2. Nachimas, A.; Strobel, G.A. "Agrobacterium rhizogenes promotes the initial growth of bare root stock almond." Microbiology. 1985. 131: 1245–1249.
3. Ron M, Kajala K, Pauluzzi G, Wang D, Reynoso MA, Zumstein K, Garcha J,Winte S, Masson H, Inagaki S, Federici F, Sinha NR, Deal R, Bailey-Serres J, Brady SM. "Hairy root transformation using Agrobacterium rhizogenes as a tool for exploring cell type-specific gene expression and function using tomato as a model." Plant Physiol. 2014. 166:455–469.
4. Brijwal L, Tamta S. Agrobacterium rhizogenes mediated hairy root induction in endangered Berberis aristata DC. SpringerPlus. 2015;4:443. doi:10.1186/s40064-015-1222-1.
5. Kajala, Kaisa, David A. Coil, and Siobhan M. Brady. “Draft Genome Sequence of Rhizobium Rhizogenes Strain ATCC 15834.” Genome Announcements 2.5 (2014): e01108–14. PMC. Web. 30 Mar. 2017.
Authored by [Isaac Tamez Salazar], a student of CJ Funk at John Brown University
