''Bradyrhizobium'' is a genus of

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 bacteria Soil microbiology is the study of microorganisms in soil, their functions, and how they affect soil properties. It is believed that between two and four billion years ago, the first ancient bacteria and microorganisms came about on Earth's oceans. ...

, many of which fix nitrogen.

Nitrogen fixation Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

is an important part of the

nitrogen cycle The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmosphere, atmospheric, terrestrial ecosystem, terrestrial, and marine ecosystems. The conversion of nitrogen can ...

. Plants cannot use atmospheric nitrogen (N₂); they must use nitrogen compounds such as

nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wa ...

Characteristics

''Bradyrhizobium'' species are Gram-negative bacilli (rod-shaped) with a single subpolar or polar

flagellum A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. They are common soil-dwelling micro-organisms that can form symbiotic relationships with

leguminous Legumes are plants in the pea family Fabaceae (or Leguminosae), or the fruit or seeds of such plants. When used as a dry grain for human consumption, the seeds are also called pulses. Legumes are grown agriculturally, primarily for human consum ...

plant species where they fix nitrogen in exchange for

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

s from the plant. Like other

rhizobia Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. I ...

, many members of this genus have the ability to fix atmospheric nitrogen into forms readily available for other organisms to use. Bradyrhizobia are also major components of forest soil microbial communities, where strains isolated from these soils are not typically capable of nitrogen fixation or nodulation. They are slow-growing in contrast to ''

Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant ce ...

'' species, which are considered fast-growing rhizobia. In a liquid medium, ''Bradyrhizobium'' species take 3–5 days to create a moderate turbidity and 6–8 hours to double in population size. They tend to grow best with

pentose In chemistry, a pentose is a monosaccharide (simple sugar) with five carbon atoms. The chemical formula of many pentoses is , and their molecular weight is 150.13 g/mol. Some strains (for example, USDA 6 and CPP) are capable of oxidizing carbon monoxide aerobically.

Taxonomy

Accepted Species

''Bradyrhizobium'' comprises the following species: * '' B. agreste'' Klepa ''et al''. 2021 * '' B. algeriense'' Ahnia ''et al''. 2019 * '' B. americanum'' Ramírez-Bahena ''et al''. 2017 * '' B. amphicarpaeae'' Bromfield ''et al''. 2019 * '' B. arachidis'' Wang ''et al''. 2013 * '' B. archetypum'' Helene ''et al''. 2020 * '' B. australiense'' Helene ''et al''. 2020 * '' B. betae'' Rivas ''et al''. 2004 * '' B. cajani'' Araújo ''et al''. 2017 * '' B. canariense'' Vinuesa ''et al''. 2005 * '' B. centrosematis'' corrig. Ramírez-Bahena ''et al''. 2017 * '' B. cosmicum'' Wasai-Hara ''et al''. 2020 * '' B. cytisi'' Chahbourne ''et al''. 2011 * '' B. daqingense'' Wang JY ''et al''. 2012 * '' B. denitrificans'' (Hirsch and Müller 1986) van Berkum ''et al''. 2011 * '' B. diazoefficiens'' Delamuta ''et al'' 2013 * '' B. diversitatis'' Serenato Klepa ''et al''. 2021 * '' B. elkanii'' Kuykendall ''et al''. 1993 * '' B. embrapense'' Delamuta ''et al.''2015 * '' B. erythrophlei'' Yao ''et al''. 2015 * '' B. ferriligni'' Yao ''et al''. 2015 * '' B. frederickii'' de Oliveira Urquiaga ''et al''. 2019 * '' B. ganzhouense'' Lu ''et al''. 2014 * '' B. glycinis'' Serenato Klepa ''et al''. 2021 * '' B. guangdongense'' Li ''et al''. 2015 * '' B. guangxiense'' Li ''et al''. 2015 * '' B. hipponense'' Rejili ''et al''. 2020 * '' B. huanghuaihaiense'' Zhang ''et al''. 2012 * '' B. icense'' Durán ''et al''. 2014 * '' B. ingae'' da Silva ''et al''. 2014 * '' B. iriomotense'' Islam ''et al''. 2010 * '' B. ivorense'' Fossou ''et al''. 2020 * '' B. japonicum'' (Kirchner 1896) Jordan 1982 ** symbiovar ''genistearum'' ** symbiovar ''glycinearum'' * '' B. jicamae'' Ramírez-Bahena ''et al''. 2009 * '' B. kavangense'' Lasse gronemeyer et al. 2015 * '' B. lablabi'' Chang ''et al''. 2011 * '' B. liaoningense'' Xu ''et al''. 1995 * '' B. lupini'' Peix ''et al''. 2015 * '' B. manausense'' Silva ''et al''. 2014 * '' B. mercantei'' Helene ''et al''. 2017 * '' B. murdochi'' Helene ''et al''. 2020 * '' B. namibiense'' Grönemeyer ''et al''. 2017 * '' B. nanningense'' Li ''et al''. 2020 * '' B. neotropicale'' Zilli ''et al''. 2014 * '' B. niftali'' Klepa ''et al''. 2019 * '' B. nitroreducens'' Jang ''et al''. 2020 * '' B. oligotrophicum'' (Ohta and Hattori 1985) Ramírez-Bahena ''et al''. 2013 * '' B. ottawaense'' Yu ''et al''. 2014 * '' B. pachyrhizi'' Ramírez-Bahena ''et al''. 2009 * '' B. paxllaeri'' Durán ''et al''. 2014 * '' B. retamae'' Guerrouj ''et al''. 2013 * '' B. rifense'' Chahboune ''et al''. 2012 * '' B. ripae'' Bünger ''et al''. 2018 * '' B. shewense'' Aserse ''et al''. 2018 * '' B. stylosanthis'' Marçon Delamuta ''et al''. 2016 * '' B. subterraneum'' Gronemeyer ''et al''. 2015 * '' B. symbiodeficiens'' Bromfield ''et al''. 2020 * '' B. tropiciagri'' Delamuta et al. 2015 * '' B. vignae'' Grönemeyer ''et al''. 2016 * '' B. viridifuturi'' Helene et al. 2015 * '' B. yuanmingense'' Yao ''et al''. 2002

Provisional Species

The following species have been published, but not validated according to the

Bacteriological Code The International Code of Nomenclature of Prokaryotes (ICNP) or Prokaryotic Code, formerly the International Code of Nomenclature of Bacteria (ICNB) or Bacteriological Code (BC), governs the scientific names for Bacteria and Archaea.P. H. A. Sneath ...

. * "''B. brasilense''" Martins da Costa ''et al''. 2017 * "''B. campsiandrae''" Cabral Michel ''et al''. 2021 * "''B. centrolobii''" Michel ''et al''. 2017 * "''B. forestalis''" Martins da Costa ''et al''. 2018 * "''B. guangzhouense''" Li ''et al''. 2019 * "''B. macuxiense''" Michel ''et al''. 2017 * "''B. sacchari''" de Matos ''et al''. 2017 * "'' Photorhizobium thompsonianum''" Eaglesham ''et al''. 1990 * "''B. uaiense''" Cabral Michel ''et al''. 2020 * "'' B. valentinum''" Durán ''et al''. 2014 * "''B. zhanjiangense''" Li ''et al''. 2019

Phylogeny

The currently accepted taxonomy is based on the

List of Prokaryotic names with Standing in Nomenclature List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the naming and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclatu ...

(LPSN). The phylogeny is based on whole-genome analysis.

Nodulation

Nodule formation

Nodules Nodule may refer to: *Nodule (geology), a small rock or mineral cluster *Manganese nodule, a metallic concretion found on the seafloor *Nodule (medicine), a small aggregation of cells *Root nodule Root nodules are found on the roots of plants, p ...

are growths on the roots of leguminous plants where the bacteria reside. The plant roots secrete

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s and sugars into 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 ...

. The rhizobia move toward the roots and attach to the

root hairs Soil biology Root hairs or absorbent hairs, are outgrowths of epidermal cells, specialized cells at the tip of a plant root. They are lateral extensions of a single cell and are only rarely branched. They are found in the region of maturation, of ...

. The plant then releases

flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...

s, which induce the expression of ''nod'' genes within the bacteria. The expression of these genes results in the production of enzymes called

Nod factor Nod factors (nodulation factors or NF), are signaling molecules produced by soil bacteria known as rhizobia in response to flavonoid exudation from plants under nitrogen limited conditions. Nod factors initiate the establishment of a symbiotic re ...

s that initiate

root hair curling Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known a ...

. During this process, the rhizobia are curled up with the root hair. The rhizobia penetrate the root hair cells with an infection thread that grows through the root hair into the main root. This causes the infected cells to divide and form a nodule. The rhizobia can now begin nitrogen fixation.

''Nod'' genes

Over 55 genes are known to be associated with nodulation. ''NodD'' is essential for the expression of the other ''nod'' genes. The two different ''nodD'' genes are: ''nodD₁'' and ''nodD₂''. Only ''nodD₁'' is needed for successful nodulation.

Nitrogen fixation

''Bradyrhizobium'' and other rhizobia take atmospheric nitrogen and fix it into ammonia (NH₃) or ammonium (NH₄⁺). Plants cannot use atmospheric nitrogen; they must use a combined or fixed form of the element. After

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

nitrogen fixation Nitrogen fixation is a chemical process by which molecular dinitrogen () is converted into ammonia (). It occurs both biologically and abiological nitrogen fixation, abiologically in chemical industry, chemical industries. Biological nitrogen ...

(or uptake) is the most important process for the growth and development of plants. The levels of ureide nitrogen in a plant correlate with the amount of fixed nitrogen the plant takes up.

Genes

''Nif'' and ''fix'' are important genes involved in nitrogen fixation among ''Bradyrhizobium'' species. ''Nif'' genes are very similar to genes found in ''

Klebsiella pneumoniae ''Klebsiella pneumoniae'' is a Gram-negative, non-motile, encapsulated, lactose- fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mo ...

'', a free-living

diazotroph Diazotrophs are organisms capable of nitrogen fixation, i.e. converting the relatively inert diatomic nitrogen (N2) in Earth's atmosphere into bioavailable compound forms such as ammonia. Diazotrophs are typically microorganisms such as bacteria ...

. The genes found in bradyrhizobia have similar function and structure to the genes found in ''K. pneumoniae''. ''Fix'' genes are important for symbiotic nitrogen fixation and were first discovered in rhizobia species. The ''nif'' and ''fix'' genes are found in at least two different clusters on the

chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...

. Cluster I contains most of the nitrogen fixation genes. Cluster II contains three ''fix'' genes located near ''nod'' genes.

Diversity

This genus of bacteria can form either specific or general symbioses; one species of ''Bradyrhizobium'' may only be able to nodulate one legume species, whereas other ''Bradyrhizobium'' species may be able to nodulate several legume species.

Ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

is highly conserved in this group of microbes, making ''Bradyrhizobium'' extremely difficult to use as an indicator of species diversity.

DNA–DNA hybridization In genomics, DNA–DNA hybridization is a molecular biology technique that measures the degree of genetic similarity between DNA sequences. It is used to determine the genetic distance between two organisms and has been used extensively in phylo ...

s have been used instead and show more diversity. However, few

phenotypic 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 ...

differences are seen, so not many species have been named. Some strains are

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

, these ''Bradyrhizobium'' often form nodules in the stems of semi-aquatic ''

Aeschynomene ''Aeschynomene'' is a genus of flowering plants in the family Fabaceae, and was recently assigned to the informal monophyly, monophyletic ''Dalbergia'' clade of the Dalbergieae. They are known commonly as jointvetches. They range across tropical ...

'' legumes, and have also been found in the nodal roots of African wild rice '' Oryza breviligulata''.

Significance

Grain legumes are cultivated on about 1.5 million km² of land per year. The amount of nitrogen fixed annually is about 44–66 million tons worldwide, providing almost half of all nitrogen used in agriculture. Commercial inoculants of ''Bradyrhizobium'' are available. ''Bradyrhizobium'' has also been identified as a contaminant of DNA extraction kit reagents and

ultrapure water Ultrapure water (UPW), high-purity water or highly purified water (HPW) is water that has been purified to uncommonly stringent specifications. Ultrapure water is a term commonly used in manufacturing to emphasize the fact that the water is treated ...

systems, which may lead to its erroneous appearance in microbiota or metagenomic datasets. The presence of nitrogen-fixing bacteria as contaminants may be due to the use of nitrogen gas in ultrapure water production to inhibit microbial growth in storage tanks.

Notable species

* ''

Bradyrhizobium betae ''Bradyrhizobium betae'' is a species of legume- root nodulating, microsymbiotic nitrogen-fixing bacterium first isolated from the roots of ''Beta vulgaris ''Beta vulgaris'' (beet) is a species of flowering plant in the subfamily Betoideae of ...

'' was isolated from tumor-like root deformations on sugar beets; they have an unknown symbiotic status. * ''

Bradyrhizobium elkanii ''Bradyrhizobium elkanii'' is a species of legume- root nodulating, microsymbiotic nitrogen-fixing bacterium originally identified as DNA homology group II strains of '' B. japonicum'' . In 1988, it was discovered that only DNA homology gro ...

'', ''

Bradyrhizobium diazoefficiens ''Bradyrhizobium diazoefficiens'' is a species of bacteria from the genus of Bradyrhizobium ''Bradyrhizobium'' is a genus of Gram-negative bacteria, Gram-negative soil bacteria, many of which fix nitrogen. Nitrogen fixation is an important par ...

'', and '' Bradyrhizobium liaoningense'' establish symbiosis with soybeans. * ''

Bradyrhizobium japonicum ''Bradyrhizobium japonicum'' is a species of legume- root nodulating, microsymbiotic nitrogen-fixing bacteria. The species is one of many Gram-negative, rod-shaped bacteria commonly referred to as rhizobia. Within that broad classification, whi ...

'' nodulates

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. Soy is a staple crop, the world's most grown legume, and an important animal feed. Soy is a key source o ...

cowpea The cowpea (''Vigna unguiculata'') is an annual herbaceous legume from the genus '' Vigna''. Its tolerance for sandy soil and low rainfall have made it an important crop in the semiarid regions across Africa and Asia. It requires very few inpu ...

mung bean The mung bean or green gram (''Vigna radiata'') is a plant species in the legume family.Brief Introduction of Mung Bean. Vigna Radiata Extract Green Mung Bean Extract Powder Phaseolus aureus Roxb Vigna radiata L R Wilczek. MDidea-Extracts P ...

s, and siratro. * '' Bradyrhizobium yuanmingense'' nodulates ''

Lespedeza ''Lespedeza'' is a genus of some 45 species (including nothospecies) of flowering plants in the pea family (Fabaceae), commonly known as bush clovers or (particularly East Asian species) Japanese clovers (''hagi''). The genus is native to warm t ...

''. * ''

Bradyrhizobium canariense ''Bradyrhizobium canariense'' is a species of legume- root nodulating, endosymbiont nitrogen-fixing bacterium. It is acid-tolerant and nodulates endemic genistoid legumes from the Canary Islands The Canary Islands (; ) or Canaries are an ...

'' nodulates genistoid legumes endemic to the

Canary Islands The Canary Islands (; ) or Canaries are an archipelago in the Atlantic Ocean and the southernmost Autonomous communities of Spain, Autonomous Community of Spain. They are located in the northwest of Africa, with the closest point to the cont ...

. It has also been found in

lupin ''Lupinus'', commonly known as lupin, lupine, or regionally bluebonnet, is a genus of plants in the legume family Fabaceae. The genus includes over 199 species, with centres of diversity in North and South America. Smaller centres occur in No ...

and serradella nodules in western Australia and southern Africa.

References

{{Taxonbar, from=Q4955276 Bacteria genera Nitrobacteraceae