biological_nitrogen_fixation.Genetic Mechanismpptx

Mechanism behind nitrogen fixation is explained

1. BIOLOGICAL NITROGEN FIXATION 1

2. Nitrogen is a component of amino acids, proteins, enzymes, Hormones, nucleic acids, vitamins etc., Nitrogen is available in atmosphere in high amount i.e ., 78% in the form of gas. 2

3. Diatomic nitrogen is inert because of the Presence of bonds between atoms. A mm o n i a 3 N i t r a t e It will be reactive or absorbed by the plants only when it is Combined with either hydrogen or oxygen as ammonia or nitrate

4. Nitrogen fixation is a process by which atmospheric nitrogen (N ₂ ) is converted into ammonia (NH ₃ ) 4

5. TYPES OF NITROGEN FIXATION 5

6. Non Biological/Natural Nitrogen Fixation During lightening and thunderstorms some amount of nitrogen is converted as nitrogen oxides, which then Dissolves in moisture to form nitrates During Volcanic emissions/Automobile emissions as Nitrogen oxides Industrial – Haber-Bosch Process is the method in Producing ammonia from nitrogen and hydrogen 6

7. Biological Nitrogen fixation may be categorized into following types : Non- Symbiotic/ asymbiotic Biological Nitrogen Fixation . B. Associative Biological Nitrogen Fixation . C. Symbiotic Biological Nitrogen Fixation 7

8. 8 A. Non- Symbiotic/ asymbiotic Biological Nitrogen Fixation: Soil contains a number of free living nitrogen fixing organisms. These include a number of aerobic and anaerobic bacteria and blue green algae. Biological nitrogen fixation by microorganisms living freely or staying out of plant cell is called non-symbiotic Biological Nitrogen Fixation The asymbiotic nitrogen fixers can be classified as follows: 1) Free living aerobic nitrogen fixing bacteria :  Photosynthetic: Chlorobium , Chromatium  Non-Photosynthetic: Azotobacter , Azomonas , Derxia , Beijerinckia 2) Free living anaerobic nitrogen fixing bacteria:  Photosynthetic: Rhodospirillum  Non-Photosynthetic: Clostridium 3) Free living chemosynthetic bacteria:  Heterotrophic: Desulfovibro 4) Cyanobacteria or Blue green algae:  Heterocyst bearing: Nostoc , Anabaena, Rivularia , Calothrix .  Non-Heterocyst bearing: Oscillatoria , Gloeocapsa , Lyngbya , Plectonema . 5) Free living Fungi:  Yeasts and Pullularia The asymbiotic free living nitrogen fixers are quite primitive. The fixation is a reduction process independent of respiration. These organisms fix nitrogen more actively under poor aeration, provided no hydrogen gas is being produced

9. 9 B. Associative Symbiotic Nitrogen Fixation: Certain bacteria, living in close contact with the roots of cereal and grasses, fix nitrogen. This association is a loose mutualism, Called associative Symbiosis. The bacteria reside in the transition zone between soil and root (the rhizosphere) and sometimes enter the roots. Some of the fixed nitrogen is absorbed by the roots and in turn the bacteria get nourishment from the carbohydrates released by the roots. Some of the examples are: 1. Azospirillum brasilense in association with cereal roots. 2. Beijerinckia in association with the roots of Sugarcane. 3. Azotobacter paspali in association with roots of tropical grass- Paspalum notatum

10. 10 Symbiotic Biological Nitrogen Fixation: Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen. Such an association between bacteria and host is ecological, long term and mutually beneficial to both, microbial partner fixes atmospheric nitrogen. The various examples of Symbiotic biological nitrogen fixation can be grouped under the following three categories: 1. Nitrogen Fixation through nodule formation in leguminous plants: Symbiotic nitrogen fixers in large number of legume plants include genus Rhizobium mainly. They established themselves inside specialized structures on the roots called root nodules. The bacteria fix nitrogen only when they are present inside the nodules. The association is regarded as symbiotic because the host plant supplies the nodule bacteria the required organic carbon (carbohydrates). In return micro-organism supply fixed nitrogen to the host plant. Bradyrhizobium japonicum is a slow growing symbiont of Soybeans. Azorhizobium caulinodans is a stem nodule forming symbiont in Sesbania species. 2. Nitrogen Fixation through nodule formation in non-leguminous plants: Many plants belonging to families other than Leguminosae are known to produce root nodules. The important among them are primarily trees and shrubs. The important examples of non-leguminous plants that produce root nodules and fix nitrogen are: 1. Genus Frankia forms root nodules in association with Alnus sp., Casuarina equisetifolia , Myrica gale, etc. 2. Rhizobium also root nodules in genus Parasponia .

11. Biological Nitrogen Fixation 11

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13. NITROGENASE ENZYME Nitrogenase is a complex enzyme containing two oxygen sensitive components. Component-I has 2 α -proteins subunits and 2 β protein subunits,24 molecules of iron,2molecules of molybdenum and an iron-molybdenum cofactor(FeMoCo). Component –II possess 2 α -proteins subunits and a large number of iron molecule . 13

14. Structure of Nitrogenase Component 1 Component 2 Nitrogenase Complex Component – I – MW : 240 – 270 KDa Dinitrogenase , Mo -2 atoms/ mol , Fe-32 atoms/ mol Component-II – MW: 55 -64kDa Dinitrogenase reductase, Fe-4 atoms mol 14

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16. HYDROGENASE It is a enzyme which uses hydrogen as the energy source. During the coarse of nitrogen fixation by nitrogenase, an undesirable reaction also occurs i,e ., reduction of H ⁺ (hydrogen ion) --->H ₂ (molecular hydrogen). For the production of hydrogen ATP is utilized, it is rather wasted. 16

17. Role of Hydrogenase Many iazotropes evolve Hydrogen (H 2 ) during Nitrogen fixation, which inturn Inhibits nitrogen fixation. Hydrogenase recycles H 2 . Reutilization of H2 produces More ATP and improves the efficiency of N 2 fixation www.hbmahesh.weebly.com 17

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19. 19 FLOW OF ELECTRONS

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21. ASYMBIOTIC OR NONSYMBIOTIC The gaseous nitrogen of the atmosphere is directly and independently utilized to produce nitrogen rich compounds . When non symbiotic organisms die, they enrich the soil with nitrogenase compounds. Ex:-Clostridium, Pasteuranium, Azatobacter chrooccum. www.hbmahesh.weebly.com 21

22. Mechanism of Nitrogen fixation in free living organisms N i t r o u s Ox i de Acetylene Hydrogen ion www.hbmahesh.weebly.com 22

23. N 2 +12 Mg ++ ATP+ 6 (H + + e - ) -----  2 NH 3 + 12 (Mg ++ ADP + pi) Overall Reaction in free living organism www.hbmahesh.weebly.com 23

24. SYMBIOTIC NITROGEN FIXATION Microorganisms live together with the plants in a mutually be ne f i c i al r e la t i o nshi p . T hi s phenomenon is referred to as ‘Symbiosis’. Most important microorganisms involved in symbiosis belong to the genera Rhizobium and Bradyrhizobium. The host plant harbouring these bacteria are known as legumes. Ex:- Soyabean, Peas, Beans, Alphapha, Peanuts and cloves. www.hbmahesh.weebly.com 24

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28. MECHANISM OF NITROGEN FIXATION IN SYMBIOTIC ORGANISMS www.hbmahesh.weebly.com 28

29. Process of Symbiotic Nitrogen Fixation. Root nodulation in legume. www.hbmahesh.weebly.com 29

30. The overall process of nitrogen fixation in a bacterioid of Rhizobium www.hbmahesh.weebly.com 30

31. Overall Reaction in Symbiotic Organisms 2NH4 + + H2 + 16 ADP + 16 pi www.hbmahesh.weebly.com 31 N2 + 16ATP + 8e - + 10H + -----  Mg ++

32. LEGHAEMOGLOBIN It is a oxygen binding protein. It contains iron and is red in colour. Lhb facilitates the appropriate transfer of oxygen to bacteria for respiration to produce ATP. The energy required for the nitrogen fixation is utilized in the form of ATP. The haem part of Lhb is synthesized by bacteria while the protein part (globin) portion is produced by host plant. www.hbmahesh.weebly.com 32

33. NITROGEN FIXING GENE OR Nif GENE The nif genes are located as a single cluster, occupying approximately 24kb of the bacterial genome. There are 7 distinct operon that encodes 20 different proteins. The nif genes are under the regulatory control of 2genes namely nif-A and nif-L. www.hbmahesh.weebly.com 33

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35. GENETICS OF NITROGEN FIXATION It is absolutely necessary to identify, isolate and characterize the nitrogen fixing gene. Transfer of genes for nitrogen fixation to bacteria helps to infect several important crops. It can form a symbiotic relationship with non leguminous plants such as wheat ,rice and corn . www.hbmahesh.weebly.com 35

36. A Map of Klebsiella -chromosome showing relative position of nif genes www.hbmahesh.weebly.com 36

37. R E G U L A T I O N O F N I T R O G E N F I X A T I O N www.hbmahesh.weebly.com 37

38. THANK YOU www.hbmahesh.weebly.com 38