''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

soil bacterium that produces hairy root disease in dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched adventitious roots at the site of infection, so-called 'hairy roots'. It also induces

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...

s. In the

rhizosphere The rhizosphere is the narrow region of soil or Substrate (biology), substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. Pore space in soil, Soil pores in the rhizosphere can ...

, plants may suffer from wounds by soil

pathogens In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term ...

or other sources. This leads to the secretion of phenolic compounds like

acetosyringone Acetosyringone is a phenolic natural product and a chemical compound related to acetophenone and 2,6-dimethoxyphenol. It was first described in relation to lignan/phenylpropanoid-type phytochemicals, with isolation from a variety of plant sour ...

which have

chemotactic Chemotaxis (from '' chemo-'' + ''taxis'') is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemica ...

effects that attract the bacteria. Under such conditions, certain bacterial genes are turned on leading to the transfer of its

T-DNA The transfer DNA (abbreviated T-DNA) is the transferred DNA of the Ti plasmid, tumor-inducing (Ti) plasmid of some species of bacteria such as ''Agrobacterium tumefaciens'' and ''Agrobacterium rhizogenes (actually an Ri plasmid)''. The T-DNA is tr ...

from its root-inducing plasmid (Ri plasmid) into the plant through the wound. After integration and expression, ''in vitro'' or under natural conditions, the hairy root

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology (physical form and structure), its developmental processes, its biochemical and physiological propert ...

is observed, which typically includes overdevelopment of a root system that is not completely geotropic, and altered (wrinkled) leaf morphology, if leaves are present. ''R. rhizogenes'' also propagates as a seed-borne pathogen. Bacterial genes may be retained within the plant, and

sweet potato The sweet potato or sweetpotato (''Ipomoea batatas'') is a dicotyledonous plant in the morning glory family, Convolvulaceae. Its sizeable, starchy, sweet-tasting tuberous roots are used as a root vegetable, which is a staple food in parts of ...

for instance has retained and actively expresses ''A. rhizogenes'' genes which are not present in other members of its genus. The hairy roots are grown ''in vitro'' in

bioreactor A bioreactor is any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical reaction, chemical process is carried out which involves organisms or biochemistry, biochem ...

s to study their soil interaction with other pathogens like

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

and

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s. This technique has also led to the commercial production of certain metabolic compounds that the plant is known to secrete, especially in regard to the medicinal plants that are difficult to cultivate in sufficient quantities by other means. The root cultures are also used for

genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of Genetic engineering techniques, technologies used to change the genet ...

Applications

Strain K84 produces agrocin 84, a type of

bacteriocin Bacteriocins are proteinaceous or peptide, peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). They are similar to yeast and paramecium killing factors, and are structurally, functionally ...

, that inhibits the growth of ''

Agrobacterium tumefaciens ''Agrobacterium tumefaciens'' (also known as ''Rhizobium radiobacter'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Symptoms are cause ...

'' (possibly a misclassified '' A. radiobacter'') which causes the disease. Strain K1026, which is descended from K84 by the removal of potentially-pathogenic DNA sequences, has been used as a

biopesticide A biopesticide is a biological substance or organism that damages, kills, or repels organisms seens as pests. Biological pest management intervention involves predatory, parasitic, or chemical relationships. They are obtained from organisms incl ...

on stone fruit (such as cherries and plums), nut trees, and ornamentals to protect them from crown gall disease. Strain K84 and its descendant K1016 are now properly classified as belonging to ''

Rhizobium rhizogenes ''Rhizobium rhizogenes'' (formerly ''Agrobacterium rhizogenes'') is a Gram-negative soil bacterium that produces hairy root disease in Dicotyledon, dicotyledonous plants. ''R. rhizogenes'' induces the formation of proliferative multiple-branched ...

''. They were formerly considered ''A. radiobacter''.

References

{{Taxonbar, from=Q138216, from2=Q26280580 Rhizobiaceae Bacteria described in 2001