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: [1] |
Agrobacterium rhizogenes
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).
Figure 2: Agrobacterium Rhizogenes, Gram stain 1000X magnification, Brightfield Microscopy PC: Simon Sublime - Exploring the Invisible
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 (6). 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 (5). Likewise, the project showed that the analyzed strain contains 6,919 predicted coding sequences and 54 predicted RNAs.
b. Briefly describe any extra-chromosomal elements or genetic tools that are used to study the bacterium: viruses, plasmids, transposons that allow genetic manipulation and analysis.
c. Has the genome or genomes been sequenced? If so, include the website for the database and one or two highlights of the genome. Also indicate genome size (base pairs), %G+C (nucleotide base composition) and number of genes, and specific genes or gene regions that are unique to this organism. If it has not been sequenced, give its closest relative that has been sequenced, its website, and some general information about the related sequence.
Automated annotation was performed using the RAST annotation server (12). R. rhizogenes strain ATCC 15834 contains 6,919 predicted coding sequences and 54 predicted RNAs. A full-length (1,416 bp) 16S sequence was obtained from this annotation and was used to confirm the Rhizobium species by comparison to 54 publicly availably Agrobacterium 16S sequences by MUSCLE alignment (13), which was used to construct a phylogenetic tree with FastTree 2 (14).
R. rhizogenes ATCC 15834 has been used to induce hairy root cultures in many biotechnology and research applications (5, 6) and its genome sequence will provide a resource for further studies of how the hairy root disease is induced.
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?
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)?
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?
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
