THE NITROGEN CYCLE

2. THE NITROGEN CYCLE • Explore the cyclical interconversion of N2 and its compounds via covering: • Nitrogen fixation • Nitrification • Denitrification • Nitrate assimilation • Ammonification • Ammonia assimilation

3. Biogeochemical Cycles • Recycling (oxidation and reduction) of chemical elements

9. Food webs are feeding relationships among the members of a community. • However, in addition to describing who eats who, they also illustrate: • Energy flow through the community • Functional feeding groups • Potentially important ecological interactions • Thus, food webs help us understand ecosystem ecology.

10. Geochemical Cycles • About 25 of the 92 natural elements are known to be essential to life.  • Just four of these – carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) – make up 96% of living matter. 

12. Nitrogen Cycle Microbial decomposition Proteins and waste products Amino acids Microbial ammonification Amino acids (–NH2) Ammonia (NH3) Nitrosomonas Ammonium ion (NH4+) Nitrite ion (NO2- ) Nitrobacter Nitrite ion (NO2-) Nitrate ion (NO3- ) Pseudmonas Nitrate ion (NO3-) N2 Nitrogen - fixation N2 Ammonia (NH3)

13. Nitrogen • What is Nitrogen?   Nitrogen makes up approximately 78% of air (by weight) and is the second most abundant element in the human body.  Although ecosystems receive an essentially inexhaustible influx of solar energy, chemical elements are available only in limited amounts and must be continually recycled.  For nitrogen, this recycling process is known as the nitrogen cycle (illustrated below). 

15. Formation of a Root Nodule Figure 27.5

16. The three components involved to make this happen are ammonia (NH³ or NH³+4), nitrite (NO²), and nitrate (NO³).

17. Nitrogen Cycle • The nitrogen cycle of an aquarium is a chain reaction in nature resulting in the birth of various types of nitrifying bacteria, each with their own job to do. Each new bacteria born consumes the previous one, and in turn gives birth to the next bacteria.

18. The Nitrogen Cycle Figure 27.4

19. The Carbon Cycle Figure 27.3

20. The Nitrogen Cycle Figure 27.4

21. Nitrogen Cycle Microbial decomposition Proteins and waste products Amino acids Microbial ammonification Amino acids (–NH2) Ammonia (NH3) Nitrosomonas Ammonium ion (NH4+) Nitrite ion (NO2- ) Nitrobacter Nitrite ion (NO2-) Nitrate ion (NO3- ) Pseudmonas Nitrate ion (NO3-) N2 Nitrogen - fixation N2 Ammonia (NH3)

22. Formation of a Root Nodule Figure 27.5

23. The Sulfur Cycle Figure 27.7

24. Sulfur Cycle Microbial decomposition Proteins and waste products Amino acids Microbial dissimilation Amino acids (–SH) H2S Thiobacillus H2S SO42– (for energy) Microbial & plant assimilation SO42– Amino acids

25. Life Without Sunshine • Primary producers in most ecosystems are photoautotrophs • Primary producers in deep ocean and endolithic communities are chemoautotrophic bacteria Provides energy for bacteria which may be used to fix CO2 H2S SO42– Calvin Cycle CO2 Sugars Provides carbon for cell growth

26. The Phosphorous Cycle

27. Degradation of Synthetic Chemicals • Natural organic matter is easily degraded by microbes • Xenobiotics are resistant to degradation

28. Decomposition by Microbes Figure 27.8

29. Decomposition by Microbes • Bioremediation • Use of microbes to detoxify or degrade pollutants; enhanced by nitrogen and phosphorus fertilizer • Bioaugmentation • Addition of specific microbes to degrade of pollutant • Composting • Arranging organic waste to promote microbial degradation Figure 27.9

30. Decomposition by Microbes Figure 27.10

32. NITROGEN IS ESSENTIAL FOR LIFE • Nitrogen is required for amino acids, proteins etc. • The major reservoir for nitrogen on Earth • is the atmosphere. • N2 is extremely stable NN.

33. NITROGEN FIXATION • The ability to use N2 is of great ecological importance. • Main types of N2 fixing microbes: • Free living bacteria e.g. Clostridium, Klebsiella that fix N2 anaerobically. • Rhizobium species in the root nodules of leguminous plants. • Actinomycetes (Frankia) in root nodules of non-leguminous plants e.g. alder tree. • Free-living cyanobacteria e.g. Anabaena. • Symbiotic cyanobacteria (lichens). • Free living aerobic microbes loosely associated with plant roots. • e.g. Azotobacter

34. FACTORS INFLUENCING N2 FIXATION Overall reaction: N2 + 8H+ + 8e- 2NH3 + H2 nitrogenase enzyme complex (MoFe protein) • Soil pH • Supply of carbon • Soil O2 status • 4. Addition of nitrogen fertiliser

35. Rhizobium nodules (arrowed) on the roots of young white Clover.

36. The legume/Rhizobium association • Legume sends out a chemical signal, lectin. • Invasion of legume root hair by Rhizobium. • Root cells/bacterial cells multiple to form nodule. • Rhizobial cells cease motile habit (bacteroid). • Leghaemoglobin protects the O2 sensitive nitrogenase enzyme system.

37. ADVANTAGE TO LEGUME • Fixed nitrogen from the atmosphere. • ADVANTAGES TO Rhizobium • A habitat free of competition. • A steady supply of photosynthate carbon.

38. Frankia nodules and cells Root nodules on the common alder tree. Vesicles on the tips of hyphal filaments. Fig. 19.75

39. Fig. 12.80 Cyanobacteria

40. Lichens Fig. 19.54/5

41. Azotobacter cells grown under a reduced oxygen concentration 2.5% Azotobacter cells grown in 21% oxygen. Fig. 17.71

42. NITRIFICATION • Oxidation of NH3, via NO2- to NO3- • Carried out by chemolithotrophic bacteria Nitrosomonas and Nitrobacter. Energy yields Nitrosomonas – 8.8 ATP molecules per mole of NH4+ Nitrobacter – 2.5 ATP molecules per mole of NO2- compare with A mole of glucose oxidizied aerobically yields 38 ATP molecules.

43. ENVIRONMENTAL CONSEQUENCES OF NITRIFICATION • Nitrate  mobile anion (compare with) • Ammonium  immobile cation • Leaching • a. Eutrophication • b. Hazardous to human health • (50 ppm NO3- EEC legal limit for drinking water) • ‘blue-baby disease/ methaemoglobinaemia • Chemical Inhibitors • Nitrapyrin – inhibits the activity of Nitrosomonas

44. DENITRIFICATION The process where nitrate replaces oxygen as the electron acceptor in soil microbial respiration. Facultative anaerobes, dominantly heterotrophic bacteria e.g. Pseudomonas and Alcaligenes. Nitrogen is lost either as N2 or N2O ENVIRONMENTAL CONSEQUENCES OF DENITRIFICATION 1. Can reduce eutrophication. 2. Costly in agricultural terms.

45. NITRATE ASSIMILATION AND AMMONIA ASSIMILATION Bacteria and fungi require a source of N for growth. NO3- is reduced for use as a nutrient source i.e. assimilated. AMMONIFICATION The formation of ammonia from dead organic nitrogen containing compounds. Rapidly recycled by microbes and plants!

46. Summary: Fig. 19.29

47. Further Reading Brock Biology of Microorganisms Section 19.12 The Nitrogen Cycle Section 12.3 Nitrifying Bacteria Section 12.9 N2-fixing bacteria Section 19.22 Root nodule bacteria and symbiosis with legumes.

48. What is a Jaubert/Plenum Filter? • Plenum is an integral part of a complete biological filter, • The popular Live Sand Filter is the brain child of Dr. Dean Jaubert. This innovative filtration system consists of a Deep Sand Bed (DSB), a plenum and a protein skimmer. • converting ammonia to nitrite, which is converted to nitrate (via aerobic bacteria), which is in turn converted to nitrogen (via anaerobic bacteria). • A protein skimmer is the primary filter in a Jaubert Filter, removing a majority of the ammonia generating DOC's (Dissolved Organic Compounds), which are created by tank critter detritus, uneaten food and other decaying matter in the tank. Understanding the principles of foam fractionating (protein skimming) will greatly assist you as you design a new system or upgrade an existing one.

49. A protein skimmer is the primary filter in a Jaubert Filter, removing a majority of the ammonia generating DOC's (Dissolved Organic Compounds), which are created by tank critter detritus, uneaten food and other decaying matter in the tank. Understanding the principles of foam fractionating (protein skimming) will greatly assist you as you design a new system or upgrade an existing one

50. Biological filter media, providing surface area for beneficial nitrosoma and nitrobacter nitrifying bacteria to grow on. • Gas barrier, keeping CO2 in the plenum and O2 the upper level of the Live Sand, allowing the filter to function properly.