Agrobacterium

• Agrobacteria are those used to carry tumour-inducing (Ti) or root-inducing (Ri) conjugative megaplasmids needed for virulence.

Agrobacteria, also known as Agrobacterium, are a genus of gram-negative bacteria that have unique properties, particularly their ability to transfer a portion of their DNA, known as the Ti (tumor-inducing) plasmid, into the genomes of plants. This natural genetic transfer mechanism has made Agrobacteria highly valuable in biotechnology and genetic engineering.

The general properties of Agrobacteria are:

1. Plant Pathogens: Agrobacteria are considered plant pathogens as they can cause diseases in various plant species. They are responsible for a condition called crown gall disease, which leads to the formation of tumor-like growths (galls) on infected plants. The Ti plasmid plays a crucial role in this disease by integrating a specific DNA fragment called T-DNA into the plant genome, causing uncontrolled cell division and gall formation.
2. T-DNA Transfer: Agrobacteria are known for their unique ability to transfer T-DNA from the Ti plasmid to plant cells. This transfer occurs through a complex process called horizontal gene transfer, where the bacteria form a physical connection with plant cells and deliver the T-DNA into the nucleus of the host cell. The T-DNA integrates into the plant genome, leading to the expression of genes that can manipulate plant cell growth and physiology.
3. Genetic Engineering Tool: The natural ability of Agrobacteria to transfer DNA into plant cells has been harnessed for genetic engineering purposes. Researchers have modified the Ti plasmid to remove disease-causing genes and replace them with desired genes of interest. Agrobacterium-mediated transformation is widely used to introduce new genetic material into plants, including crop plants, for traits such as pest resistance, herbicide tolerance, and enhanced nutritional content.
4. Soil-Dwelling Bacteria: Agrobacteria are commonly found in soil environments. They have a saprophytic lifestyle, meaning they can obtain nutrients by decomposing organic matter present in soil. Agrobacteria establish a symbiotic relationship with the plant root system by forming structures called rhizospheres, where they benefit from plant root exudates and, in return, provide certain nutrients to the plant.
5. Broad Host Range: Agrobacteria have a broad host range and can infect a wide variety of plant species, including dicots and some monocots. This versatility makes them useful in genetic engineering applications as they can be employed to introduce genetic modifications into a diverse range of plants.
6. Agrocin Production: Some strains of Agrobacterium produce antimicrobial compounds called agrocins. Agrocins are known to inhibit the growth of other bacteria, including closely related Agrobacterium strains. These antimicrobial properties contribute to the competitiveness of Agrobacteria in their natural soil habitats.

Overall, Agrobacteria possess unique properties that have made them invaluable tools in plant biotechnology. Their ability to transfer DNA into plants has revolutionized genetic engineering and has allowed for the development of genetically modified crops with improved traits.