Nitrogen and sulfur cycles

2. By
Ahmad Mayla
Microbiology Department
2010
NITROGEN CYCLE
IN MICROBIAL POINT OF VIEW

3. NUTRIENT CYCLE
• Biogeochemical cycle or nutrient cycle. It is a pathway by
which a chemical element or molecule moves through both biotic and
abiotic (lithosphere, atmosphere, and hydrosphere) compartments of
Earth.
• It describes the movement of chemical elements
through the biological and geological
component of the world
• Key Nutrient Cycles

7. HISTORY
• Daniel Rutherford chemist and physician who
discovered Nitrogen in 1772. He removed oxygen and
carbon dioxide from air and showed that :
The residual gas would not support
combustion nor living organisms
• Laurent Lavoisier mistakenly named nitrogen azote
meaning without life.

8. FORMS OF NITROGEN
• Atmospheric N2
• Ammonia  NH3 (gaseous)
• Ammonium  NH4
+
• Nitrate  NO3
-
• Nitrite  NO2
-
• Organic Nitrogen
• Urea  CO(NH2)2

9. CYCLING OF NITROGEN
• Four processes participate in the cycling of
nitrogen through the biosphere:
1. Nitrogen Fixation
2. Decay ( Ammonification).
3. Nitrification
4. Denitrification
• Microorganisms play major roles in all four of
these.

11. NITROGEN ATOM

12. OXIDATION STATES

13. NITROGEN IS A KEY ELEMENT FOR
• Amino acids
• Nucleic acids (purine, pyrimidine)
• Cell wall components of many bacteria
(Peptidoglycan)

14. NITROGEN IS A KEY ELEMENT FOR
• All life requires nitrogen-compounds, e.g., proteins and nucleic acids.
• Air, which is 79% nitrogen gas (N2), is the major reservoir of nitrogen.
• But most organisms cannot use nitrogen in this form.
• Plants must secure their nitrogen in "fixed" form, i.e., incorporated in
compounds such as:
• nitrate ions (NO3
−)
• ammonia (NH3)
• urea (NH2)2CO
• Animals secure their nitrogen compounds from plants (or animals that
have fed on plants).

15. SOURCES OF FIXED NITROGEN
• Lightning
• Inorganic fertilizers
• Nitrogen Fixation
• Animal Residues
• Crop residues
• Organic fertilizers

17. NITROGEN FIXATION
• Three processes are responsible for
most of the nitrogen fixation in the
biosphere:
1. Atmospheric fixation by
lightning
2. Biological fixation by certain
microbes alone or in a
symbiotic relationship with
some plants and animals
3. Industrial fixation

18. BIOLOGICAL NITROGEN FIXATION
• The nitrogen molecule (N2) is quite inert. To break it apart so that its atoms
can combine with other atoms requires the input of substantial amounts of
energy.
• Biological nitrogen fixation requires a complex set of enzymes (nitrogenase)
and a huge expenditure of ATP.
• Although the first stable product of the process is ammonia, this is quickly
incorporated into protein and other organic nitrogen compounds
16 ATP 2NH3

19. BIOLOGICAL NITROGEN FIXATION
• The ability to fix nitrogen is found only in certain bacteria and archaea
Methanogens ,e.g.
1. Symbionts
1. Rhizobium, Bradyrhizobium with plants of the legume family (e.g.,
soybeans, alfalfa).
2. Frankia with plants other than legumes (e.g., alders, casuarina ).
3. Cyanobacteria with fungi in lichens & with Azolla
4. Xylophaga atlantica & X.washingtona with (wood-eating bivalves).
5. Some with shipworms or termites
2. Free-living
1. Aerobic Fixation :Azotobacter, Cyanobacteria
2. Anaerobic Fixation :Clostridium, Purple & Green Bacteria Chlorobi
3. Some Spirochetes
• Nitrogen-fixing cyanobacteria are essential to maintaining the fertility of
semi-aquatic environments like paddies (rice fields).

20. Examples Of Nitrogen-fixing Bacteria (* Denotes A Photosynthetic Bacterium)
Free Living Symbionts
Aerobic Anaerobic
Symbiotic With Animals Symbiotic With Plants
Wood-eating
Bivalves
Shipworms Termites Legumes
Other Plants
(e.g., alders,
casuarina )
1. Azotobacter
2. Beijerinckia
3. Klebsiella
(Some)
4. Cyanobacter
ia (Some)*
1. Clostridium
(Some)
2. Desulfovibrio
3. Purple Sulfur
Bacteria*
4. Purple Non-
Sulfur Bacteria*
5. Green Sulfur
Bacteria*
Xylophaga
atlantica
X.
washingtona
1. Rhizobium
2. Bradyrhizobi
um
1. Frankia
2. Azospirillum

21. RATES OF NITROGEN FIXATION
N2 fixing system Nitrogen Fixation
(kg N/hect/year)
Rhizobium-legume 200-300
Cyanobacteria- moss 30-40
Rhizosphere
associations
2-25
Free- living 1-2

22. NH4
+
NO2
-
NO3
-
N2 -NH2
Nitrification
Ammonification
Assimilation
Assimilation
Anammox
Brocadia

26. INCREASED NITROGEN FIXATION
1. Loss of soil nutrients (calcium, potassium)
2. Competition bet. microbes and plants for
nutrients.
2. Acidification of rivers and lakes (fertilizers and
combustion of coal).
3. Increases nitrogen oxides in the atmosphere
(greenhouse gas—global warming).
(reduce ozone—increasing UV penetration).

28. INCREASED NITROGEN FIXATION
4. Aids in spreading weeds into nitrogen poor
areas
5. Eutrophication, the accumulation of dissolved
nutrients in a body of water of lakes, ponds
& streams.
6. the "blooms" of algae in lakes and rivers as
nitrogen fertilizers leach from the soil of
adjacent farms (and lawns).

29. 5. Increasing nitrogen increases carbon
fixation (linked to carbon cycle).
6. Increasing acidification increases
weathering (increases rate of phosphorous
cycle)
INCREASED NITROGEN FIXATION

30. INCREASED DENITRIFICATION
1. Detrimental process removes fixed
nitrogen (NH3, NO3
-)from environment
• Causes agricultural problem in nitrate-
fertilized waterlogged fields (anoxic
conditions enhance NO2
-  N2 )after
heavy spring rains
2. Very beneficial process in wastewater
treatment
• Minimizes algal blooms in discharged
water into lakes and streams

31. INCREASED NITRIFICATION
• If materials high in protein, such as manure or sewage, are added to soils, the rate
of nitrification is increased which leads to algal blooms in lakes and rivers.
• Algal blooms are formed due to eutrophication.
• Eutrophication, the accumulation of dissolved nutrients ,e.g. nitrates, in a body
of water of lakes, ponds & streams (How?)
• By Leaching Of Nitrates :-
• Manure, sewage, etc
• NH4
+ + Soil- = Electric Absorption
( Facilitates assimilation)
• NO3
- + Soil - = Repulsion

32. SOLUTION
1. Anhydrous ammonia as nitrogen fertilizer (NH3)
2. Nitrapyrin, substituted pyridine compound :
1. Prevents pollution by leached nitrates
2. Increases efficiency of fertilization
x

33. CHECK
1. Why does nitrogen reservoir pool be gaseous and not sedimentary?
2. What is nitrogen fixation?
3. Why is it important?
4. What are the processes called that result in NH4
+ N2?
5. How do the processes of nitrification and denitrification differ?
6. While -------- is the process of nitrate consumption, -------- is the process of
nitrate production
7. Why does NO3
- assimilation occur only in oxic conditions?
8. Ammonia produced by -------------- or -----------------. It can be assimilated into
organic matter or oxidized to nitrate.
9. ………………………. and …………….. result in losses of nitrogen gas from the
biosphere.
10. How does the compound nitrapyrin benefit both agriculture and the
environment?

34. BY
Ahmad M. Mayla
Microbiology

35. INTRODUCTION
 Sulfur cycle is complex due to:
1. Wide range of oxidation states -2+6
2. Rates of some transformations are chemically and
biologically equal

36. Only 3 oxidation states form significant amount of sulfur in nature

37. Reservoirs of sulfur
1. Sedimentary
1. Sulfate minerals, Gypsum(CaSO4)
2. Sulfide minerals, Pyrite(FeS2, golden yellow)
FeS2 --- O2,Δ-- > Fe2O3 +SO2 (industry)
1. Fluid (aqueous, marine):
Inorganic sulfate

38. H2S
 Volatile
 Predominates in acidic pH
 Toxicity:
 H2S+Fe(of cells cytochromes & other compounds)
 Environmental detoxification:
 H2S + Fe  FeS (insoluble & black)
FeS --- dil. HCl --- > FeCl2 + H2S (in lab)

39. Marine pollution
 Sewage, sludge, garbage…. marine ecosystem
 In marine sediments the rate of sulfate reduction is
1. Carbon limited (?)
2. Increased by addition of organic matter

40. H2S oxidizer, Beggiatoa
 Aerobic
 Chemolithoheterotroph

41. Sulfur oxidizer, Thiobacillus
 Aerobic
 Chemolithoautotroph

42. Photosynthetic sulfur bacteria
2H2S + CO2 ---– Light, Bacteriochlorophyll --- > (CH2O)n + 2S +H2O

44. DMS
 Biogenic gas emitted
from sea ,4.5 million
ton annually
 Produced by anoxic
degradation of
Dimethyl
Sulfoniopropionate
DMSP (osmoregulatory
solute in marine algae).
 Electron donor for PSB

45. DMS cooling effect
 Major Natural Source Of Atmospheric
Sulfur
 Contributes To
 Tropospheric Sulfur Burden
 Particle Formation And Growth In The
Atmosphere.
 The Atmospheric Sulfate Aerosol
Particles That Evolve From
Biogenically-derived DMS Emissions
Play A Role In The Global Radiation
Balance
 Directly Through The Upward Scatter
Of Solar Radiation
 Indirectly As Cloud Condensation
Nuclei (CCN).

46. DMS cooling effect
 Scientists have sequenced the genome
of the microorganism Silicibacter
pomeroyi, a member of an abundant
group of marine bacteria known to
impact the Earth’s ecosystem by
releasing and consuming atmospheric
gases. This genetic blueprint provides
insight into the biochemical pathways
the bacterium uses to regulate its
release of sulfur and carbon
monoxide. Atmospheric sulfur serves
as a catalyst for cloud formation, in
turn, directly affecting the planet’s
temperature and energy regulation,
while carbon monoxide is a
greenhouse gas (Science Daily, Dec.
24, 2004).

52. Thiobacillus,
Sulfolobus
Archaeoglobus (H2)
PSB, GSB
Assimilation
Desulfurylation
Sulfur Disproportionation
Desulfovibrio
Geochemical sources
1. Volcanoes
2. Sulfide Springs
SRB (Org.):
1. Desulfovibrio,
2. Desulfobacter,
3. Desulfomonas

53. ‫ان‬‫وعرف‬ ‫شكر‬
‫قال‬
‫هللا‬ ‫رسول‬
–
‫وسلم‬ ‫عليه‬ ‫هللا‬ ‫صلى‬
-
:
"
‫ال‬
‫يشكر‬ ‫ال‬ ‫من‬ ‫هللا‬ ‫يشكر‬
‫الناس‬
"
.1
‫للدكتورة‬ ‫شكرى‬ ‫بخالص‬ ‫أتقدم‬ ‫لذا‬
‫غزالن‬ ‫حنان‬
‫المستمرة‬ ‫لنصائحها‬
‫التعليم‬ ‫وجودة‬ ‫الطالب‬ ‫بشؤون‬ ‫واهتمامها‬
.2
‫والتفاعل‬ ‫االستماع‬ ‫لحسن‬ ‫األعزاء‬ ‫زمالئى‬ ‫وأشكر‬

54. ‫المجلس‬ ‫كفارة‬ ‫دعاء‬