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BIOLOGICAL NITROGEN FIXATION

BIOLOGICAL NITROGEN FIXATION. Beberapa tumbuhan dapat membentuk senyawa yang mengandung N dari udara Melalui bakteri yang memfiksasi N inilah N atmosfir memasuki biosfer (lingkungan makhluk hayati) Bakteri pemfiksasi N mereduksi N atmosfir menjadi amonia (NH 3 )  NH 4 +

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BIOLOGICAL NITROGEN FIXATION

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  1. BIOLOGICAL NITROGEN FIXATION KRT-2011

  2. Beberapa tumbuhan dapat membentuk senyawa yang mengandung N dari udara • Melalui bakteri yang memfiksasi N inilah N atmosfir memasuki biosfer (lingkungan makhluk hayati) • Bakteri pemfiksasi N mereduksi N atmosfir menjadi amonia (NH3)  NH4+ • Terdapat 2 bakteri yang memfiksasi N yaitu: Bakteri yang hidup bebas dan Bakteri yang bersimbiosis  Rhizobium sp. • Bakteri mampu memanfaatkan berbagai sumber nitrogen untuk sintesis protein • Nitrogen merupakan elemen dari molekul biologis, spt: asam amino, nucleotides, protein dan DNA KRT-2011

  3. The Nitrogen Cycle • Mineralization: Organic nitrogen (mostly amino acids)  NH4+(All organisms) • Nitrification: NH4+ NO2- (Nitrosomonas) NO2- NO32- (Nitrobacter) • Denitrification: NO3- N2O N2O  N2(Several species, including certain Pseudomonas and Bacillus) KRT-2011

  4. The Nitrogen Cycle • Assimilatory Nitrate Reduction NO32- Organic Nitrogen (Many microbial species and plants) • N2 fixation N2 NH4+ Free-living nitrogen fixers eg Azotobacter and Azospirillum Symbiotic nitrogen fizers eg Rhizobium and BradyrhizobiumCyanobacteria attached to the cordgrass plant Spartina in salt marshes (=rawa?) KRT-2011

  5. Most plants depend on bacteria to supply nitrogen KRT-2011

  6. The Nitrogen Cycle KRT-2011

  7. General view of nitrogen metabolism KRT-2011

  8. Pathways Involved in Nitrogen Utilization 1. Protein Digestion – by proteinase & peptidase 2. Oxidative Deamination KRT-2011

  9. 3. Reductive Deamination 4. Decarboxylation KRT-2011

  10. 5. Transamination Reactions KRT-2011

  11. 6. Nitrification 7. Denitrification KRT-2011

  12. Industrial Fixation • Di bawah tekanan tinggi, pada suhu 600oC, dan dengan penggunaan catalyst, nitrogen dan hydrogen atmosfir (biasanya turunan dari natural gas atau petroleum) dapat bergabung untuk membentuk ammonia (NH3). • Ammonia dapat digunakan secara langsung sebagai pupuk, tetapi umumnya diproses lebih lanjut menjadi ureadan ammonium nitrate (NH4NO3). KRT-2011

  13. Biological Fixation • Kemampuan untuk memfiksasi nitrogen hanya ditemukan dalam bacteria tertentu. • Beberapa hidup dalam symbiotic relationship dengan tanaman dari famili legume (e.g., kedelai, alfalfa). • Beberapa ada yang bersimbiosis dengan tanaman selain legumes (e.g., alders). • Beberapa bakteri fiksasi-nitrogen hidup bebas dalam tanah • Nitrogen-fixing cyanobacteria penting untuk mempertahankan kesuburan dari lingkungan semi-aquatic seperti lahan padi KRT-2011

  14. Biological Fixation cont. • Biological nitrogen fixation membutuhkan serangkaian enzymes dan penghasil ATP yang sangat besar. • Meskipun produk stabil pertama dari proses adalah ammonia, ini cepat diinkorporasi ke dalam protein dan senyawa nitrogenorganic lain • Para ilmuwan memperkirakan bahwa biological fixation secara global menambah kira-kira 140 million metric tons nitrogen kedalam ecosystems setiap tahun. KRT-2011

  15. Some nitrogen fixing organisms • Free living aerobic bacteria • Azotobacter • Beijerinckia • Klebsiella • Cyanobacteria (lichens) • Free living anaerobic bacteria • Clostridium • Desulfovibrio • Purple sulphur bacteria • Purple non-sulphur bacteria • Green sulphur bacteria • Free living associative bacteria • Azospirillum • Symbionts • Rhizobium (legumes) • Frankia (alden trees) KRT-2011

  16. Some nitrogen fixing organisms KRT-2011

  17. Estimated Average Rates of Biological N2 Fixation KRT-2011

  18. Rank of Biological Nitrogen Fixation KRT-2011

  19. Nitrogen Fixation • Semua bacteria fiksasi nitrogen menggunakan conserved enzyme complex yang disebut Nitrogenase • Nitrogenase tersusun dari dua subunits: an iron-sulfur protein dan a molybdenum-iron-sulfur protein • Aerobic organisms face special challenges to nitrogen fixation karena nitrogenase inactivasi bila oxygen bereaksi dengan iron component of the proteins KRT-2011

  20. Nitrogenase FeMo Cofactor Fd(ox) Fd(red) N2 + 8H+ 8e- 2NH3 + H2 nMgATP nMgADP + nPi 4C2H2 + 8H+ 4C2H2 Dinitrogenase reductase Dinitrogenase N2 + 8H+ + 8e- + 16 MgATP  2NH3 + H2 + 16MgADP KRT-2011

  21. Nitrogenase KRT-2011

  22. Types of Biological Nitrogen Fixation Free-living (asymbiotic) • Cyanobacteria • Azotobacter Associative • Rhizosphere–Azospirillum • Lichens–cyanobacteria • Leaf nodules Symbiotic • Legume-rhizobia • Actinorhizal-Frankia KRT-2011

  23. Free-living N2 Fixation Energy • 20-120 g C used to fix 1 g N Combined Nitrogen • nif genes tightly regulated • Terhambat pada NH4+ and NO3- rendah (1 μg g-1 soil, 300 μM) Oxygen • Menghindar (anaerobes) • Microaerophilly • Respiratory protection • Specialized cells (heterocysts, vesicles) • Spatial/temporal separation • Conformational (=penyesuaian diri?) protection KRT-2011

  24. Heterocyst KRT-2011

  25. Associative N2 Fixation • Phyllosphere or rhizosphere (tropical grasses) • Azosprillum, Acetobacter • 1 to 10% of rhizosphere population • Beberapa berada dalam akar • Same energy and oxygen limitations as free-living • Acetobacter diazotrophicus hidup dalam internal tissue dari tebu, tumbuh dalam 30% sucrose, dapat mencapai populasi 106 sampai 107 cells g-1 tissue, dan memfiksasi 100 to 150 kg N ha-1 y-1 KRT-2011

  26. Phototrophic N2-fixing Associations • Lichens–cyanobacteria and fungi • Mosses and liverworts–some have associated cyanobacteria • Azolla-Anabaena (Nostoc)–cyanobacteria dalam batang water fern CGunnera-Nostoc–cyanobacteria dalam batang nodule dari dicot CCycas-Nostoc–cyanobacteria dalam akar gymnosperm KRT-2011

  27. Azolla pinnata (left) 1cm. Anabaena from crushed leaves Of Azolla. KRT-2011

  28. Simbiosis Anabaena-Azolla KRT-2011

  29. Frankia and Actinorhizal Plants • Actinomycetes (Gram +, filamentous); septate hyphae; spores in sporangia; thick-walled vesicles Frankia vesicles showing thick walls that confer protection from oxygen. Bars are 100 nm. KRT-2011

  30. Alder and the other woody hosts of Frankia are typical pioneer species that invade nutrient-poor soils. These plants benefit from the nitrogen-fixing association, while supplying the bacterial symbiont with photosynthetic products. KRT-2011

  31. Actinorhizal Plant Hosts KRT-2011

  32. Legume-Rhizobium Symbiosis • The subfamilies of legumes(Caesalpinioideae, Mimosoideae, Papilionoideae), 700 genera, and 19,700 species of legumes • Only about 15% of the species have been evaluated for nodulation • Rhizobium • Gram -, rod • Most studied symbiotic N2-fixing bacteria • Now subdivided into several genera • Many genes known that are involved in nodulation (nod, nol, noe genes) KRT-2011

  33. Taxonomy of Rhizobia KRT-2011

  34. Rhizobium Root Nodules The picture above shows a clover root nodule. Available from [Internet] KRT-2011

  35. Rhizobium Root Nodules KRT-2011

  36. A few legumes (such as Sesbania rostrata) have stem nodules as well as root nodules. Stem nodules (arrows) are capable of photosynthesis as well as nitrogen fixation. KRT-2011

  37. Formation of a Root Nodule KRT-2011

  38. Nodulation in Legumes KRT-2011

  39. Infection Process • Menempel • Rambut akar menggulung • Degradasi dinding sel setempat • Infection thread • Differensiasi Cortical cell • Rhizobia melepas ke dalam cytoplasm • Bacteroid differentiation (symbiosome formation) • Induksi dari nodulins KRT-2011

  40. General Amino sugars, sugars Specific Flavones (luteolin), isoflavones (genistein), flavanones, chalcones Inducers/repressors of nod genes Berbeda tergantung species tanaman Responsiveness varies by rhizobia species Role of Root Exudates KRT-2011

  41. nod Gene Expression Common nod genes Nod factor–LCO (lipo-chitin oligosaccharide) KRT-2011

  42. Nodule Metabolism Oxygen metabolism • Variable diffusion barrier • Leghemoglobin Nitrogen metabolism • NH3 diffuses to cytosol • Assimilation by GOGAT • Conversion to organic-N for transport Carbon metabolism • Sucrose converted to dicarboxylic acids • Functioning TCA in bacteroids • C stored in nodules as starch KRT-2011

  43. Synthesis of Cellular Components Reaksi dikatalisis oleh enzim nitrogenase KRT-2011

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