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CHAPTER 9 Biogeochemical Cycling

CHAPTER 9 Biogeochemical Cycling. Last finished task: 9.3.1 Nitrogen Pool 9.3.2 Nitrogen Fixation ( 固氮 ) 9.3.3 Ammonium Assimilation （氨的同化） Ammonium Ammonification （氨化作用）. Today’s task: 9.3.4 Nitrification （硝化作用） 9.3.5 Nitrate Reduction （硝酸盐还原作用）

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CHAPTER 9 Biogeochemical Cycling

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  1. CHAPTER 9 Biogeochemical Cycling

  2. Last finished task: 9.3.1 Nitrogen Pool 9.3.2 Nitrogen Fixation (固氮) 9.3.3 Ammonium Assimilation （氨的同化） Ammonium Ammonification （氨化作用） Today’s task: 9.3.4 Nitrification （硝化作用） 9.3.5 Nitrate Reduction （硝酸盐还原作用） 9.3.5.1 Assimilatory Nitrate Reduction (同化硝酸盐还原) 9.3.5.2 Dissimilatory Nitrate Reduction （异化硝酸盐还原) ） outline

  3. Taihu Lake

  4. Lake Dian

  5. N is a main factor causing the eutrophication of water. Now,a lot of chemicals containing nitrogen is discharged into water and results in serious eutrophication.So,how to get rid of the nitrogenous pollutants?The key includes the N cycle in chapter 9.

  6. Returned mixtures？ Wastewater Anoxic tank Aerobic tank Effluent Secondary settling tank Returned sludge ? Excess Sludge Nitrogen RemovalProcess ：A /O process N2 缺氧池 好氧池 ??? ?? 回流污泥 剩余物污泥

  7. 9.3 NITROGEN CYCLE

  8. The “question” that need answering after class: How to get rid of the pollutants containing nitrogenin a bodyofwater?

  9. 9.3.4 Nitrification 9.3.4.1 The definition for Nitrification : 9.3.4.2 Nitrifier(nitrifyingbacteria硝化细菌） 9.3.4.3 The characteristics of nitrifier

  10. 9.3.4.1 The definition for Nitrification Nitrificationis the microbially catalyzed conversion of ammonium(铵) to nitrate（硝酸盐）. Nitrificationis the process by which ammonia is changed by microorganisms to nitrite（亚硝酸盐）,then,nitrate.

  11. 9.3.4 Nitrification

  12. 9.3.4.2. Nitrifier(nitrifyingbacteria硝化细菌） Nitrifier arethe bacteria that oxidize ammonia to nitriteandnitrateincluding two genera: (1) Nitrosomonas(亚硝化单胞菌)which oxidizes ammonium to nitrite(亚硝酸盐); (2) Nitrobacter(硝化细（杆）菌)which oxidizes nitrite to nitrate（硝酸盐）。

  13. Nitrosomonas

  14. Nitrobacter

  15. Culture of nitrifying bacteria

  16. Chemoautotrophic Nitrifying Bacteria Genus （属） Species（种） Ammonium oxidizers（铵氧化细菌） Nitrosomonas （亚硝化单胞菌属）europaea（欧洲亚硝化单胞菌） eutrophus（富营养亚硝化单胞菌） marina（海洋亚硝化单胞菌） Nitrosococcus （硝化球菌属） nitrosus（硝化硝化球菌） mobilis（活动硝化球菌） oceanus（海洋硝化球菌） Nitrosospira （亚硝化螺菌属） briensis（白里亚硝化螺菌） Nitrosolobus （亚硝化叶菌属） multiformis（多形亚硝化叶菌） Nitrosovibrio （亚硝化弧菌属） tenuis（纤细亚硝化弧菌） Nitrite oxidizers（亚硝酸盐氧化菌） Nitrobacter（硝化杆菌属） winogradskyi（维氏硝化杆菌） hamburgensis（汉堡硝化杆菌） vulgaris（普通硝化杆菌） Nitrospina（硝化刺菌属） gracilis（纤细硝化刺菌） Nitrococcus （硝化球菌属） mobilis（活动硝化球菌） Nitrospira（硝化螺菌属） marina（海洋硝化螺菌）

  17. “Genus(genera)” - biological classification that combines organisms sharing common characteristics; ranks between species and family. "Species" is the smallest unit of classification. A common definition of species is that of a group of organisms capable of interbreeding and producing fertile offspring.

  18. Nitrosomonas NH4+ NO2- Ammonium Nitrite Nitrobacter NO2- NO3- Nitrate Nitrite

  19. 9.3.4.3 The Characteristics of Nitrifier （硝化细菌） (The Factors Influencing nitrification) 1、Autotrophy(自养作用) The Nitrosomonas and Nitrobacter are autotrophicbacteria. These organisms obtain energy by oxidizing ammonia or nitrite. NH4++ O2 + 2H+ → NH2OH+H2O →NO2 -+ 5H+ ΔG =-66 kcal (Eq. 9.6) hydroxylamine NO2-+ 0.5 O2 + 2H+→ NO3- + 5H+ ΔG =-66 kcal (Eq. 9.6)

  20. 2、Temperature Optimum（最适） temperature of nitrifiers is 15~35℃. 3、pH The optimum pH for nitrification is 6.6 to 8.0. In environmentswith pH 6.0,nitrification rates are slowed, and below pH 4.5, nitrification seems to be completely inhibited.

  21. 3、 Alkalinity （碱度） Oxidization of1g of ammoniaconsumes 7.14g of alkalinity(CaCO3carbonic acid). 4、Symbiosis(共生) These two types of nitrifiers are generally found together in the environment. As a result, nitrite does not normally accumulate in the environment.

  22. 5、Strict aerobes Nitrifying bacteria are strict aerobes.They can not live in the environment lacking oxygen. 6.Longer generation time(代时) The growth rate of nitrifying bacteria is very slow.The generation time of them is generally 8h to several days.

  23. 9.3.5 Nitrate Reduction 9.3.5.1 Assimilatory（同化的） nitrate reduction ornitrate immobilization. Nitrate can be taken up and incorporated（掺入）into living biomass（生物质、生物量）by microorganisms. The uptake of nitrate is followed by its reduction to ammonium, which is then incorporated into biomass.This process is called assimilatory nitrate reduction or nitrate immobilization.

  24. （1）Ammonium is incorporated into（掺入）α-ketoglutarate（α-酮戊二酸） to form glutamate. Fig. 9.10A

  25. (2)The second ammonium uptake pathway isthe reaction Whichis driven by ATP and two enzymes, glutamine(谷氨酰胺) synthase(合成酶) and glutamate synthetase(谷氨酸合成酶) Fig.9.10B

  26. Most microbes utilize ammonium preferentially, when it is present,to avoid having to reduce nitrate to ammonium,a process requiring energy. So if ammonium is present in the environment, assimilatory nitrate reduction is suppressed.

  27. 9.3.5.2 Dissimilatory nitrate reduction (异化硝酸盐还原) There are two separate dissimilatory nitrate reduction processes, both of which are used by facultative chemoheterotrophic organisms(兼性化能异养微生物)under microaerophilic or anaerobic conditions(微好养或厌氧条件下):

  28. 1、Dissimilatory Nitrate Reduction to Ammonium (DNRA) 铵异化硝酸盐还原 The first process, called dissimilatory nitrate reduction to ammonia (DNRA), uses nitrate as a terminal electron acceptor to produce energy to drive the oxidation of organic compounds.The end product of DRNA is ammonium: NO3-+ 4H2 + 2H+ → NH4++3H2O △G =-144 kcal/8e- transfer

  29. The first step in this reaction, the reduction of nitrate to nitrite, is the energy-producing step; • The further reduction of nitrite to ammonium is catalyzed by an NADH-dependent reductase; • Under carbon-limiting conditions nitrite accumulates (denitrification predominates); • Under carbon-rich conditions ammonium is the major product (DNRA predominates);

  30. A second environmental factor that selects for DNRA is low levels of available electron acceptors. • Therefore , this process is found predominantly in carbon-rich environments such as stagnant(不流动的) water, sewage sludge（污泥）, some high-organic-matter sediments.

  31. Bacteria That Utilize Dissimilatory Nitrate or Nitrite to Ammonium (DRNA)

  32. 2、Denitrification The second type of dissimilatory nitrate reduction is known as denitrification. （1）The definition for denitrification Denitrification refers to the microbial reduction ofnitrate to N2.

  33. （2）The significance of denitrification This is the primary type of dissimilatory nitrate reduction because it cycles fixed nitrogen back into N2： NO3- +5H2 + 2H+→N2+ 6H2O △G= -212 kcal/8e-transfer

  34. 反硝化细菌

  35. The four steps involved in denitrification are shown in more detail in Fig. 9.12.

  36. The first step, • reduction ofnitrate to nitrite, • is catalyzed by the enzyme nitrate reductase（硝酸盐还原酶）. • Both the synthesisand the activity of nitrate reductase are inhibited byoxygen.

  37. The second enzyme in this pathwayis nitrite reductase（亚硝酸盐还原酶）, which catalyzes the conversionof nitrite tonitric oxide(NO)（一氧化氮）. Synthesis of nitrite reductase is inhibited by oxygen and induced（诱导） by nitrate.

  38. Nitrite reductase is found in the periplasm（周质空间） and exists in two forms, a copper-containing form and a heme（亚铁血红素） form, both of which are distributed widely in the environment.

  39. The third enzymeisnitric oxide reductase（一氧化氮还原酶）,a membrane-bound (与膜结合的)protein, in the pathway, catalyzing the conversion of nitric oxide（一氧化氮NO） to nitrous oxide（一氧化二氮 N2O）.The synthesis of this enzyme is inhibited by oxygen and induced by various nitrogen oxide forms（各种氮氧化物）. • The last enzymeisnitrous oxide reductase in the pathway and converts nitrous oxide to dinitrogen gas.

  40. The activity of the nitrous oxide reductase enzyme is inhibited by low pH and is even more sensitive to oxygen than the other three enzymes in the denitrification pathway. Thus, nitrous oxide is the final product of denitrification under conditions of high oxygen and low pH.

  41. The Factors Influencing Denitrification 1、Chemoheterotrophic bacteria (异养菌) 2、Temperature Optimum（最适） temperature10~35℃. 3、 pH The optimum pH for denitrification is 7.0 to 7.5. Below pH 6.0 or above 8.0 nitrification is almost completely inhibited.

  42. 4、 Alkalinity （碱度） Denitrifying bacteria produce alkalinity(CaCO3 carbonic acid ) . 3.0g CaCO3/NO3-N

  43. In summary, both the synthesis and activity of denitrification enzymes are controlled by oxygen. Enzyme activity is more sensitive to oxygen than enzyme synthesis as shown in Fig. 9.13. The amount of dissolved oxygen in water is as little as 0.5 mg/L or less inhibits the activity of denitrification enzymes.

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