Nitrogen fixation is a chemical process by which molecular dinitrogen is converted into ammonia. It occurs both biologically and abiologically in chemical industries. Biological nitrogen fixation or diazotrophy is catalyzed by enzymes called nitrogenases. These enzyme complexes are encoded by the Nif genes and contain iron, often with a second metal.
Pseudomonadota is a major phylum of Gram-negative bacteria. Currently, they are considered the predominant phylum within the realm of bacteria. They are naturally found as pathogenic and free-living (non-parasitic) genera. The phylum comprises six classes Acidithiobacillia, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Hydrogenophilia, and Zetaproteobacteria. The Pseudomonadota are widely diverse, with differences in morphology, metabolic processes, relevance to humans, and ecological influence.
In agriculture, cover crops are plants that are planted to cover the soil rather than for the purpose of being harvested. Cover crops manage soil erosion, soil fertility, soil quality, water, weeds, pests, diseases, biodiversity and wildlife in an agroecosystem—an ecological system managed and shaped by humans. Cover crops can increase microbial activity in the soil, which has a positive effect on nitrogen availability, nitrogen uptake in target crops, and crop yields. Cover crops reduce water pollution risks and remove CO2 from the atmosphere. Cover crops may be an off-season crop planted after harvesting the cash crop. Cover crops are nurse crops in that they increase the survival of the main crop being harvested, and are often grown over the winter. In the United States, cover cropping may cost as much as $35 per acre.
Trichodesmium, also called sea sawdust, is a genus of filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters. Trichodesmium is a diazotroph; that is, it fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms. Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts.
Burkholderia is a genus of Pseudomonadota whose pathogenic members include the Burkholderia cepacia complex, which attacks humans and Burkholderia mallei, responsible for glanders, a disease that occurs mostly in horses and related animals; Burkholderia pseudomallei, causative agent of melioidosis; and Burkholderia cepacia, an important pathogen of pulmonary infections in people with cystic fibrosis (CF). Burkholderia species is also found in marine environments. S.I. Paul et al. (2021) isolated and characterized Burkholderia cepacia from marine sponges of the Saint Martin's Island of the Bay of Bengal, Bangladesh.
The Burkholderiales are an order of Betaproteobacteria in the phylum Pseudomonadota. Like all Pseudomonadota, they are Gram-negative. They include several pathogenic bacteria, including species of Burkholderia, Bordetella, and Ralstonia. They also include Oxalobacter and related genera, which are unusual in using oxalic acid as their source of carbon. Other well-studied genera include Alcaligenes, Cupriavidus, Achromobacter, Comamonas, Delftia, Massilia, Duganella, Janthinobacterium, Polynucleobacter, non-pathogenic Paraburkholderia, Caballeronia, Polaromonas, Thiomonas, Collimonas, Hydrogenophaga, Sphaerotilus, Variovorax, Acidovorax, Rubrivivax and Rhodoferax, and Herbaspirillum.
Azotobacter is a genus of usually motile, oval or spherical bacteria that form thick-walled cysts and may produce large quantities of capsular slime. They are aerobic, free-living soil microbes that play an important role in the nitrogen cycle in nature, binding atmospheric nitrogen, which is inaccessible to plants, and releasing it in the form of ammonium ions into the soil. In addition to being a model organism for studying diazotrophs, it is used by humans for the production of biofertilizers, food additives, and some biopolymers. The first representative of the genus, Azotobacter chroococcum, was discovered and described in 1901 by Dutch microbiologist and botanist Martinus Beijerinck. Azotobacter species are Gram-negative bacteria found in neutral and alkaline soils, in water, and in association with some plants.
Burkholderia cepacia complex (BCC) is a species complex consisting of Burkholderia cepacia and at least 20 different biochemically similar species of Gram-negative bacteria. They are catalase-producing and lactose-nonfermenting. Members of BCC are opportunistic human pathogens that most often cause pneumonia in immunocompromised individuals with underlying lung disease. Patients with sickle-cell haemoglobinopathies are also at risk. The species complex also attacks young onion and tobacco plants, and displays a remarkable ability to digest oil.
Burkholderia pseudomallei is a Gram-negative, bipolar, aerobic, motile rod-shaped bacterium. It is a soil-dwelling bacterium endemic in tropical and subtropical regions worldwide, particularly in Thailand and northern Australia. It was reported in 2008 that there had been an expansion of the affected regions due to significant natural disasters, and it could be found in Southern China, Hong Kong, and countries in the Americas. B. pseudomallei, amongst other pathogens, has been found in monkeys imported into the United States from Asia for laboratory use, posing a risk that the pathogen could be introduced into the country.
Burkholderia mallei is a Gram-negative, bipolar, aerobic bacterium, a human and animal pathogen of genus Burkholderia causing glanders; the Latin name of this disease (malleus) gave its name to the species causing it. It is closely related to B. pseudomallei, and by multilocus sequence typing it is a subspecies of B. pseudomallei.B. mallei evolved from B. pseudomallei by selective reduction and deletions from the B. pseudomallei genome. Unlike B. pseudomallei and other genus members, B. mallei is nonmotile; its shape is coccobacillary measuring some 1.5–3.0 μm in length and 0.5–1.0 μm in diameter with rounded ends.
Betaproteobacteria are a class of Gram-negative bacteria, and one of the eight classes of the phylum Pseudomonadota.
Paraburkholderia phymatum is a species of bacteria that is capable of symbiotic nitrogen fixation with the legumes Machaerium lunatum and Mimosa pudica. Recently, the genome was sequenced. It consists of two chromosomes, a megaplasmid, and a plasmid hosting the symbiotic functions.
Paraburkholderia phytofirmans is a species of bacteria. They have been reported to colonize endophytic tissues of hybrid spruce and lodgepole pine with a strong potential to perform biological nitrogen fixation and plant growth promotion.
Paraburkholderia tuberum is a species of bacteria that is capable of symbiotic nitrogen fixation with the legume Aspalathus carnosa.
Bradyrhizobium is a genus of Gram-negative soil bacteria, many of which fix nitrogen. Nitrogen fixation is an important part of the nitrogen cycle. Plants cannot use atmospheric nitrogen (N2); they must use nitrogen compounds such as nitrates.
Paraburkholderia sprentiae is a Gram-negative, rod-shaped bacterium from the genus Paraburkholderia and the family Burkholderiaceae which was isolated from root nodules from the plant Lebeckia ambigua in South Africa.
Cyanothece is a genus of unicellular, diazotrophic, oxygenic photosynthesizing cyanobacteria.
Paraburkholderia is a genus of Pseudomonadota that are gram negative, slightly curved rods that are motile by means of flagella. They have been reported to colonize endophytic tissues of hybrid spruce and lodgepole pine with a strong potential to perform biological nitrogen fixation and plant growth promotion. Unlike Burkholderia species, Paraburkholderia members are not commonly associated with human infection. Paraburkholderia members form a monophyletic clade within the Burkholderiaceae family, which is what prompted their distinction as a genus independent from Burkholderia species, in combination with the finding of robust conserved signature indels which are unique to Paraburkholderia species, and are lacking in members of the genus Burkholderia. These CSIs distinguish the genus from all other bacteria. Additionally, the CSIs that were found to be shared by Burkholderia species are absent in Paraburkholderia, providing evidence of separate lineages.
Caballeronia is a genus of bacteria from the family of Burkholderiaceae which has been reported to perform biological nitrogen fixation and promote plant growth
Perry William Wilson was an American microbiologist and biochemist. He gained a scientific reputation as an outstanding pioneer in transforming the science of biological nitrogen fixation. His research helped to transform a mainly descriptive science into a more quantitative and analytic science based on biochemistry and statistical methods and control in bacteriology. He was called the "dean of biological nitrogen fixation".
