Nitrogen fixation-types of nitrogen fixation.pptx

nitrogen fixation, any natural or industrial process that causes free nitrogen (N2), which is a relatively inert gas plentiful in air, to combine chemically with other elements to form more-reactive nitrogen compounds such as ammonia, nitrates, or nitrites.

1. Sub title: Organic farming and Biofertilizer technology Sub code: 22MBPGSEC2 Title: NITROGEN FIXATION SUBMITTED BY M.Sherniha , II MSc, Microbiology PG and Research Department of Microbiology Sri Paramakalyan College Alwarkunchi 627412 SSUBMITTED TO Dr. S. Viswanathan , M.Sc., Ph.D. Head and Associate Professor PG and Research Department of Microb i o lo gy Sr i Paramakalyani College Alwankuroni-627412

2. Content: Aim and objective Introduction Nomenclature History Nitrogen fixation Types of nitrogen fixation Biological nitrogen fixation Non biological nitrogen fixation Industrial nitrogen fixation Symbiotic nitrogen fixation Free living nitrogen fixation Factors affecting N2 fixation Significance Reference

3. Aim: To provide a comprehensive understanding of the process of nitrogen fixation, its significance in agriculture and the environment, and the role of nitrogen-fixing organisms. Objectives: To explain the concept and chemical process of nitrogen fixation, converting atmospheric nitrogen into usable forms like ammonia. To discuss biological nitrogen fixation by bacteria such as Rhizobium and Azotobacter, and their symbiotic relationships with plants. To highlight the importance of nitrogen fixation in plant growth, soil fertility, and sustainable agriculture. To provide knowledge about different types of nitrogen fixation including biological, industrial, and atmospheric processes. To explore methods to enhance nitrogen fixation for improved crop yields and environmental benefits.

4. Nitrogen can be found in many forms in our environment. Nitrogen is also very important for plants to live. The earth's atmosphere is made up of 78 percent nitrogen in the form of a colorless , odorless , nontoxic gas. The same nitrogen gas found in the atmosphere can be found in spaces between soil particles. However, plants are unable to use this form of nitrogen. Certain microorganisms found in the soil are able to convert atmospheric nitrogen into forms plants can use. This is called  biological nitrogen fixation . Introduction

5. 📖 Nomenclature The term 'nitrogen' really refers to the N atom, and the gas which com-poses 80% of our atmosphere, N₂, is correctly termed dinitrogen. This term will be adopted here but, since the more colloquial 'nitrogen' is still widely used for the process of nitrogen fixation, I shall continue to use it in that particular context. 'Fixed nitrogen' will refer to any compound of N that is not N, but may have originated therefrom. Other technical terms will be explained as they arise; those which specially concern the nitrogen cycle are discussed in the next five sections.

6. ◀️ History Our understanding of nitrogen fixation goes back to the 18th century and continues today: 1768: Carlos Linnaeus:  This famous Swedish botanist was among the first to note that certain plants, which were later identified as legumes, grew well in soils that were considered too poor to support most other plants. 1823: Jean-Baptiste Boussingault :  A French agricultural chemist, Boussingault was the first to conclusively demonstrate that plants do not directly absorb free nitrogen from the air. His studies also hinted that legume plants had a unique method of nitrogen acquisition. 1886: Hermann Hellriegel and Hermann Wilfarth :  These German agronomists discovered the key to how legumes acquire nitrogen. They found that nodules on legume roots fix atmospheric nitrogen. When these nodules were absent or ineffective, the plants couldn’t thrive in nitrogen-deficient soils. 1901: Martinus Beijerinck :  This Dutch microbiologist identified that the bacteria living within these root nodules were the real heroes of the nitrogen fixation process. He showed that Rhizobium bacteria in the nodules converted atmospheric nitrogen into a form plants could use. 1918: Fritz Haber:  While his work wasn’t directly related to biological nitrogen fixation, this German chemist’s invention of the  Haber Process  revolutionized nitrogen fixation on an industrial scale, allowing for large-scale synthesis of ammonia. This had major implications for agriculture, providing an artificial source of fixed nitrogen for fertilizers.

7. 🌍 Nitrogen fixation Nitrogen fixation is the process by which atmospheric nitrogen gas (N₂) is converted into ammonia (NH₃) or related biologically useful forms such as ammonium (NH₄⁺), nitrite (NO₂⁻), or nitrate (NO₃⁻). Although nitrogen gas constitutes ~78% of the Earth’s atmosphere, it is chemically inert because of the triple bond (N≡N) between the two nitrogen atoms. Most organisms cannot utilize atmospheric nitrogen directly, so it must first be fixed into a reactive form. This process is crucial for maintaining the nitrogen cycle, which sustains life on Earth by ensuring nitrogen availability for plant and microbial growth.

8. 🔁 Nitrogen Cycle (Overview) 1. Nitrogen fixation → converts N₂ to NH₃. 2. Nitrification → NH₃ → NO₂⁻ → NO₃⁻. 3. Assimilation → plants use nitrates to form proteins. 4. Ammonification → decomposers return NH₃ to soil. 5. Denitrification → Pseudomonas, Bacillus convert NO₃⁻ → N₂.

9. Types of Nitrogen Fixation A. Biological Nitrogen Fixation (BNF) Carried out by prokaryotic microorganisms (bacteria and archaea) possessing the enzyme nitrogenase. Examples: Free-living bacteria : Azotobacter, Clostridium, Cyanobacteria (e.g., Anabaena, Nostoc). Symbiotic bacteria : Rhizobium, Bradyrhizobium , Frankia. B. Physical or Abiotic Fixation Occurs through lightning or industrial processes. Lightning: The high temperature converts N₂ + O₂ → NO + NO₂ → nitrates (NO₃⁻) which dissolve in rainwater. Industrial (Haber–Bosch process): N₂ + 3H₂ → 2NH₃ under high temperature (500°C), pressure (200 atm), and iron catalyst.

10. 🍃 Biological Nitrogen Fixation (Mechanism) Enzyme System: Nitrogenase Complex Composed of two proteins: Dinitrogenase reductase (Fe-protein): Transfers electrons from ferredoxin or flavodoxin. 2. Dinitrogenase ( MoFe -protein): Reduces N₂ to NH₃.The process is ATP-dependent and oxygen-sensitive. B. Overall Reaction N_2 + 8H^+ + 8e^- + 16ATP → 2NH_3 + H_2 + 16ADP + 16PiC. Protection from Oxygen Oxygen inactivates nitrogenase. Strategies used by microorganisms: Leghemoglobin in legume nodules binds O₂. Heterocysts in cyanobacteria provide anaerobic environment. High respiratory rates in Azotobacter consume excess O₂.

11. 2️⃣ Physical (Non-Biological) Nitrogen Fixation ⚡ Definition: Conversion of atmospheric nitrogen to nitrogen oxides ( NO, NO₂ ) by natural physical processes , such as lightning . 🔥 Process: Lightning provides high energy to break the N≡N bond. N₂ reacts with O₂ to form nitric oxide (NO) and nitrogen dioxide (NO₂) . These gases dissolve in rainwater to form nitric acid (HNO₃) and nitrous acid (HNO₂) . These acids reach the soil through precipitation , forming nitrate (NO₃⁻) and nitrite (NO₂⁻) ions. 🔬 Reaction Sequence: 🌧️ Significance: Supplies small but important quantities of nitrate to soils. More significant in tropical regions with high lightning activity.  

12. 3️⃣ Industrial Nitrogen Fixation 🏭 Definition: Human-mediated processes that fix nitrogen chemically under high temperature and pressure to synthesize ammonia for fertilizers and other industrial uses. ⚙️ Most Common: Haber–Bosch Process 📌 Process: Developed by Fritz Haber and Carl Bosch in the early 20th century. Reacts nitrogen (N₂) and hydrogen (H₂) under: Temperature: 400–500°C Pressure: 150–200 atm Catalyst: Iron (Fe) with potassium/ aluminum promoters N2​+3H2​450°C,200atmFe catalyst​2NH3​ 🧨 Source of H₂: Mostly obtained from natural gas (methane). 📦 Products: Ammonia (NH₃), which is converted into: Urea Ammonium nitrate Ammonium sulfate 🌍 Importance: Enabled the Green Revolution by mass production of fertilizers. Supports global food production for billions of people. However, excessive use can lead to eutrophication , soil degradation , and greenhouse gas emissions (N₂O) .

13. 🌱 4. Symbiotic Nitrogen Fixation (Rhizobium-Legume Example) A. Infection Process Recognition: Plant root secretes flavonoids that attract Rhizobium . Attachment: Bacteria attach to root hairs. Infection Thread Formation: Bacteria enter root hair through a tubular infection thread. Nodule Formation: Cortical cells divide to form a nodule. Bacteroid Differentiation: Inside nodules, bacteria transform into bacteroids (nitrogen-fixing form). B. Role of Leghemoglobin Leghemoglobin (pink pigment) maintains low oxygen concentration for nitrogenase activity while allowing enough O₂ for bacterial respiration

14. Free-living nitrogen fixation is the process by which microorganisms, such as bacteria and archaea, convert atmospheric nitrogen gas (N2) into ammonia (NH3) without forming a symbiotic relationship with a host plant. This process is crucial for the global nitrogen cycle, making nitrogen—a vital nutrient for all life—available to ecosystems .  Examples of free-living nitrogen-fixing bacteria Azotobacter :  An  aerobic  (oxygen-using) bacterium found in soil.  Clostridium :  An anaerobic (oxygen-avoiding) bacterium that performs nitrogen fixation.  Klebsiella :  A heterotrophic bacterium that can fix nitrogen in the soil.  Cyanobacteria :  Photosynthetic bacteria that also contribute to free-living nitrogen fixation.  🦠Free-living nitrogen fixation

15. ☑️ Applications in Biotechnology Biofertilizers : Formulated using Rhizobium , Azotobacter , Azospirillum , Anabaena– Azolla . Genetic Engineering: Transfer of nif (nitrogen fixation) genes to non-leguminous crops like rice and wheat. Sustainable Agriculture: Eco-friendly nitrogen input. ‼️Factors Affecting Nitrogen Fixation Oxygen concentration – must be controlled. Carbon source availability – provides energy. Soil pH and temperature – optimal range is neutral to slightly acidic. Mineral nutrients – Fe, Mo, Co required as cofactors. Presence of nitrates/ammonia – represses nitrogenase activity (feedback inhibition).

16. 🌿 Significance of Nitrogen Fixation 1. Increases Soil Fertility: Converts atmospheric nitrogen into plant-available forms. 2. Reduces Dependence on Synthetic Fertilizers. 3. Maintains Ecological Nitrogen Balance. 4. Supports Sustainable Agriculture: Through use of biofertilizers . 5. Enhances Crop Productivity: Especially in legumes and rice fields.

17. 📑References Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley , W. M., & Stahl, D. A. (2022). Brock Biology of Microorganisms (16th ed.). Pearson Education. Willey, J. M., Sherwood, L. M., & Woolverton , C. J. (2020). Prescott’s Microbiology (11th ed.). McGraw-Hill Education. Tortora , G. J., Funke , B. R., & Case, C. L. (2021). Microbiology: An Introduction (13th ed.). Pearson Education.

18. When Adversity Knocks A frustrated girl asked her father for advice on dealing with life's difficulties. He asked her to bring an egg, two tea leaves, and a potato. He boiled them separately: the egg became hard, the potato softened, and the tea changed the water's color and flavor. He explained that adversity affects us unlike it does others—some become hardened, some softened, and some even transform their environment. The girl learned that how one responds to hardship is a personal choice. Moral: We choose how to respond to adversity in life, shaping our character and destiny. MORAL STORY

19. learning outcomes for a topic on nitrogen fixation: Understand the process of nitrogen fixation and its importance in ecosystems. 2. Identify the different types of nitrogen fixation (symbiotic, asymbiotic , free-living). 3. Recognize the role of nitrogen-fixing microorganisms in sustainable agriculture. 4. Analyze the benefits and limitations of nitrogen fixation in various ecosystems.