''Bradyrhizobium japonicum'' is a species of

legume A legume () is a plant in the family Fabaceae (or Leguminosae), or the fruit or seed of such a plant. When used as a dry grain, the seed is also called a pulse. Legumes are grown agriculturally, primarily for human consumption, for livestock f ...

nitrogen-fixing Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atm ...

bacteria. The species is one of many

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name '' Baci ...

bacteria commonly referred to as rhizobia. Within that broad classification, which has three groups,

taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

studies using DNA sequencing indicate that ''B. japonicum'' belongs within

homology Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor * Sequence homology, biological homology between DNA, RNA, or protein sequences *Homologous chrom ...

group II.

Uses

Agriculture

''B. japonicum'' is added to legume seed to improve crop yields, particularly in areas where the bacterium is not native (e.g.

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the Osage ...

soils). Often the inoculate is adhered to the seeds prior to planting using a sugar solution.

Research

A strain of ''B. japonicum'', USDA110, has been in use as a model organism since 1957. It is widely used to study

molecular genetics Molecular genetics is a sub-field of biology that addresses how differences in the structures or expression of DNA molecules manifests as variation among organisms. Molecular genetics often applies an "investigative approach" to determine the ...

, plant physiology, and

plant ecology Plant ecology is a subdiscipline of ecology which studies the distribution and abundance of plants, the effects of environmental factors upon the abundance of plants, and the interactions among and between plants and other organisms. Examples ...

due to its relatively superior symbiotic nitrogen-fixation activity with

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...

(i.e. compared to other rhizobia species). Its entire

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...

was sequenced in 2002, revealing that the species has a single

circular chromosome A circular chromosome is a chromosome in bacteria, archaea, Mitochondrial DNA#Genome structure and diversity, mitochondria, and Chloroplast DNA#Molecular structure, chloroplasts, in the form of a molecule of circular DNA, unlike the linear chromo ...

with 9,105,828 base pairs.

Metabolism

''B. japonicum'' is able to degrade

catechin Catechin is a flavan-3-ol, a type of secondary metabolite providing antioxidant roles in plants. It belongs to the subgroup of polyphenols called flavonoids. The name of the catechin chemical family derives from ''catechu'', which is the tanni ...

with formation of phloroglucinol carboxylic acid, further decarboxylated to

phloroglucinol Phloroglucinol is an organic compound with the formula C6H3(OH)3. It is a colorless solid. It is used in the synthesis of pharmaceuticals and explosives. Phloroglucinol is one of three isomeric benzenetriols. The other two isomers are hydroxyqu ...

, which is dehydroxylated to

resorcinol Resorcinol (or resorcin) is an organic compound with the formula C6H4(OH)2. It is one of three isomeric benzenediols, the 1,3-isomer (or '' meta''-isomer). Resorcinol crystallizes from benzene as colorless needles that are readily soluble i ...

and

hydroxyquinol Hydroxyquinol is an organic compound with the formula C6H3(OH)3. It is one of three isomeric benzenetriols. The compound is a colorless solid that is soluble in water. It reacts with air to give a black insoluble solid. Production It is prepar ...

. ''B. japonicum'' possess the ''nosRZDFYLX'' gene, which aides in denitrification and has two catalytic subunits - Cu-a and Cu-z (with several histidine residues). It manages an expression cascade that can sense oxygen gradients, termed 'FixJ-FixK2-FixK1.' FixJ positively regulates FixK2, which activates nitrogen respiration genes, as well as FixK1. FixK1 mutants are unable to respire from nitrogen due to a defective catatylic copper subunit (Cu-z) in ''nosRZDFYLX''.

Genetic transformation

Natural genetic transformation in bacteria is a sexual process involving transfer of DNA from one cell to another through the intervening medium, and the integration of the donor sequence into the recipient genome by

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...

. ''B. japonicum'' cells are able to undergo transformation. They become competent for DNA uptake during late log phase.

References

External links

Bradyrhizobium on www.bacterio.cict.frType strain of ''Bradyrhizobium japonicum'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{DEFAULTSORT:Bradyrhizobium japonicum Nitrobacteraceae Gram-negative bacteria Model organisms Bacteria described in 1896