Biological Nitrogen Fixation

Discovered by : Martinus Beijerinck

Discovered in year : 1885

Biological nitrogen fixation is generally referred to the biological process by which nitrogen (N2) in the atmosphere is converted into ammonia. The growth of all organisms depends on the availability of mineral nutrients and nitrogen is required to biosynthesize the basic building blocks of life, e.g. nucleotides for DNA and amino acids for proteins. Formally, nitrogen fixation also refers to other abiological conversions of nitrogen, such as its conversion to nitrogen dioxide. N2 is cannot be used  by most organisms because there is a triple bond between the two nitrogen atoms, making the molecule almost inert. In order for nitrogen to be used for growth it must be "fixed" (combined) in the form of ammonium (NH4) or nitrate (NO3) ions. Micro-organisms like bacteria, actinobacteria and certain types of anaerobic bacteria can do this. Some of these organisms are called 'Free-Living Nitrogen-fixing Bacteria' as they live independently of other organisms while others live in intimate 'Symbiotic Associations' with plants or with other organisms (e.g. protozoa). These organisms use an enzyme called nitrogenase to convert atmospheric nitrogen into ammonia which can be easily used by various organisms including plants. Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with taxa such as clover, soybeans, alfalfa, lupines and peanuts. They contain symbiotic bacteria called Rhizobia within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants and this helps to fertilize the soil

History

Biological nitrogen fixation was discovered by the Dutch microbiologist Martinus Beijerinck. In 1885, he became a microbiologist at the Netherlands Yeast and Alcohol Manufactory in Delft where he isolated nitrogen-fixing root nodule bacteria in pure culture. He began his work studying the microorganisms that were present in and around plants. He soon began experiments with microbes in the soil. His greatest contribution was the development of enrichment media. Beijerinck discovered that by adding or removing certain compounds from the medium or incubating under different conditions, it was possible to favour the growth of certain microbes and prevent the growth of others. Beijerinck wanted to isolate an organism capable of fixing nitrogen in the presence of air, because all previous isolates fixed nitrogen only under anaerobic conditions. By making medium that did not contain a source of fixed nitrogen and then incubating in the presence of air (containing N2), he postulated that any microbe growing in the medium had to be able to derive its nitrogen by performing aerobic nitrogen fixation. Using this method he succeeded in isolating a new microbe (Azotobacter chroococum) with these capabilities.  

Development in the discovery of Biological nitrogen fixation

During 1890, russian microbiologist, Sergie Winogradsky successfully isolated nitrifying bacteria and also developed a model system for growing anaerobic-photosynthetic and microaerophilic soil bacteria now known as the Winogradshy’s column. He also developed the concept of microbial chemoautotrophy. He described the anaerobic nitrogen fixing bacteria and contributed to the studies of reduction of nitrates and symbiotic nitrogen fixation. He showed that nitrifying bacteria are responsible for transforming ammonia to nitrates in the soil. He originated the nutritional classification of soil microbes as Autochthonous (native) and Autochthonous (opportunistic).

In 1904, Martinus Beijerinck obtains the first pure culture of sulfur-oxidizing bacterium, Thiobacillus denitrificans. In 1909, Sigurd Orla-Jensen proposed the use of physiological characteristics for the classification of bacteria. He later published a monograph on lactic acid bacteria that establishes the criteria for assignment. By 1920, the Society of American Bacteriologists presents a report on the characterization and classification of bacterial types.

In 1961, Brian McCarthy and E. T. Bolton describe a method to compare genetic material from different species using hybridization. Using this technique it is possible to quantitatively compare the relatedness of the two species. In 1965, Emile Zuckerkandl and Linus Pauling publish "Molecules as documents of evolutionary history", making a compelling case for the use of molecular sequences of biological molecules to determine evolutionary relationships. In 1969, Don Brenner and colleagues establish a more reliable basis for the classification of clinical isolates among members of the Enterobacteriaceae. They use nucleic acid reassociation, where DNA of one organism is allowed to hybridize with another organism. This technique is used to help define a species.

Then in 1977, Carl Woese uses ribosomal RNA analysis to identify a third form of life, the Archaea, whose genetic makeup is distinct from but related to both Bacteria and Eucarya. And in 1977, Holger Jannasch discovers abundant life at the bottom of the ocean near deep sea hydrothermal vents. The entire system is dependent upon sulfur oxidizing microorganisms. Light and photosynthesis do not drive the process. By 1982, Karl Stetter isolates hydrothermophilic microbes (Archaea) that can grow at 105°C. The discovery redefines the upper temperature at which life can exist. In 1994, Gary Olsen, Carl Woese and Ross Overbeek summarize the state of phylogeny in prokaryotes. This led scientists to rethink the classification of life and emphasizes the importance of microbes.

Role of Biological Nitrogen Fixation in the improvement of human life

• It improved agricultural practices and proved that nitrogen-fixing bacteria are important in agriculture.

• Enrichment culture is still used in food industry and biotechnology.

• Further research in this process led to a better understanding of how these microrganisms work.