Context

• Two recent papers published in the journals Science and Cell have generated new interest in the endosymbiotic theory. This discovery is related to nitrogen fixation.

Key Points

• It is noteworthy that the theory of natural selection was proposed by Charles Darwin in the nineteenth century.
• Natural selection, the engine that drives evolution, is how species adapt to their environment.
• Contrary to the neo-Darwinist consensus, American evolutionary biologist Lynn Margulies did not believe that random genetic mutations were the sole cause of inherited variation.
• She came up with a new theory called symbiosis which is also known as endosymbiotic theory.
• This theory suggests that organelles such as mitochondria and chloroplasts, sites of cellular respiration and photosynthesis, were once free-living bacteria that were later ingested by recipient cells.
• The theory of symbiosis was strongly challenged, including Margulis's manuscript, which was rejected by 15 academic journals before being published in The Journal of Theoretical Biology in 1967.

New dimensions of endosymbiotic theory

• Two papers published recently in the journals Science and Cell have generated new interest in the endosymbiotic theory. This discovery is related to nitrogen fixation.
• It is noteworthy that nitrogen is a major component in the proteins and DNA of all living organisms.
• Although nitrogen gas makes up about 78% of Earth's atmosphere by volume, plants and animals lack systems that can utilize atmospheric nitrogen.
• Bacteria and archaea help convert atmospheric nitrogen gas into ammonia by nitrogen fixation (or ammonification) to make the nitrogen usable by plants.
• Unlike many free-living nitrogen-fixing bacteria, legumes, a class of plants in the Fabaceae family, harbor nitrogen-fixing bacteria in their root nodules.
• To complete the cycle, ammonia is converted to nitrite and nitrate (nitrification) and then back to atmospheric nitrogen (denitrification) with the help of bacteria.
• In marine environments, as in Earth, bacteria and archaea are also involved in ammonification, nitrification and denitrification.
• Beyond mitochondria and chloroplasts, the current discovery extends previous reports of a nitrogen-fixing cyanobacterium in seaweed and establishes it as a new organelle.
• Accordingly, the new organelle, the nitroplast, co-evolved with its host cell.

Biotechnology Applications

• The present discovery results in nitroplasts that can be used as independent nitrogen-fixing organelles.
• These involve engineering host cells and their nitroplasts with a minimal genome sufficient to grow efficiently and fix nitrogen, and introducing nitroplast and organelle transformation into plant cells to introduce the nitroplast and its host genes to fix nitrogen. They can also prove helpful in activities like fixing nitrogen to plant cells etc.
• However all these processes are highly challenging.

Implications of this discovery in agriculture

• The discovery of a method to synthesise ammonia from nitrogen and hydrogen in the laboratory in the last century transformed agriculture.
• Although the Haber-Bosch method of production on an industrial scale revolutionised agriculture by introducing ammonia as a fertiliser, which helped increase crop yields several fold, industrial ammonia production leads to water and air pollution with its carbon dioxide emissions and Contributes to climate change.
• The present discovery has the potential to play an important role in getting rid of the harmful side effects of industrial ammonia production.

Important Facts For Exam

Nitrogen

• Type: Chemical Element
• Symbol: N.
• Atomic Number: 7
• Percentage in Earth's atmosphere: 78%
• Properties: Colourless, odourless, tasteless and inert gas.
• Discovery: in 1773
• Inventor: Scottish scientist Daniel Rutherford