Transcript Cycles PPT

THE NITROGEN CYCLE
Explore the cyclical interconversion of N2 and its
compounds via covering:
•Nitrogen fixation
•Nitrification
•Denitrification
•Nitrate assimilation
•Ammonification
•Ammonia assimilation
Biogeochemical Cycles
• Recycling (oxidation and reduction) of
chemical elements
• 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.
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.
Nitrogen Cycle
Proteins and waste products
Microbial ammonification
Amino acids (–NH2)
Ammonium ion (NH4
Nitrite ion (NO2
-)
Nitrate ion (NO3
N2
-)
Nitrogen - fixation
Microbial decomposition
+)
Nitrosomonas
Nitrobacter
Pseudmonas
Ammonia (NH3)
Nitrite ion (NO2- )
Nitrate ion (NO3- )
N2
Ammonia (NH3)
Amino acids
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).
Formation of a Root Nodule
Figure 27.5
• The three components involved to make
this happen are ammonia (NH³ or NH³+4),
nitrite (NO²), and nitrate (NO³).
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.
The Nitrogen Cycle
Figure 27.4
The Carbon Cycle
Figure 27.3
The Nitrogen Cycle
Figure 27.4
Nitrogen Cycle
Proteins and waste products
Microbial ammonification
Amino acids (–NH2)
Ammonium ion (NH4
Nitrite ion (NO2
-)
Nitrate ion (NO3
N2
-)
Nitrogen - fixation
Microbial decomposition
+)
Nitrosomonas
Nitrobacter
Pseudmonas
Ammonia (NH3)
Nitrite ion (NO2- )
Nitrate ion (NO3- )
N2
Ammonia (NH3)
Amino acids
Formation of a Root Nodule
Figure 27.5
The Sulfur Cycle
Figure 27.7
Sulfur Cycle
Proteins and waste products
Amino acids (–SH)
Thiobacillus
H2S
SO4
2–
Microbial decomposition
Microbial dissimilation
H2S
SO42– (for energy)
Microbial & plant assimilation
Amino acids
Amino acids
Life Without Sunshine
• Primary producers in most ecosystems are
photoautotrophs
• Primary producers in deep ocean and
endolithic communities are
chemoautotrophic bacteria
H2 S
CO2
Provides energy for bacteria
which may be used to fix CO2
SO42–
Calvin Cycle
Sugars
Provides carbon for cell growth
The Phosphorous Cycle
Degradation of Synthetic
Chemicals
• Natural organic matter is easily degraded
by microbes
• Xenobiotics are resistant to degradation
Decomposition by Microbes
Figure 27.8
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
Decomposition by Microbes
Figure 27.10
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.
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
anaerobically.
that fix N2
•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
FACTORS INFLUENCING N2 FIXATION
Overall reaction:
N2 + 8H+ + 8e-  2NH3 + H2
nitrogenase enzyme complex (MoFe protein)
1. Soil pH
2. Supply of carbon
3. Soil O2 status
4. Addition of nitrogen fertiliser
Rhizobium nodules
(arrowed) on the roots of
young white Clover.
The legume/Rhizobium association
1. Legume sends out a chemical signal, lectin.
2. Invasion of legume root hair by Rhizobium.
3. Root cells/bacterial cells multiple to form nodule.
4. Rhizobial cells cease motile habit (bacteroid).
5. Leghaemoglobin protects the O2 sensitive nitrogenase
enzyme system.
ADVANTAGE TO LEGUME
1. Fixed nitrogen from the atmosphere.
ADVANTAGES TO Rhizobium
1. A habitat free of competition.
2. A steady supply of photosynthate carbon.
Frankia nodules and cells
Root nodules on the
common alder tree.
Vesicles on the tips of
hyphal filaments.
Fig. 19.75
Fig. 12.80
Cyanobacteria
Lichens
Fig. 19.54/5
Azotobacter cells
grown under a
reduced oxygen
concentration 2.5%
Azotobacter cells
grown in
21% oxygen.
Fig. 17.71
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.
ENVIRONMENTAL CONSEQUENCES
OF NITRIFICATION
Nitrate  mobile anion (compare with)
Ammonium  immobile cation
1. 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
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
DENITRIFICATION
1.
Can reduce eutrophication.
2.
Costly in agricultural terms.
OF
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!
Summary: Fig. 19.29
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.
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.
• 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
• 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.
Protein Skimmer
• To be as unscientific and as clear
as possible, let's simply say that the
air bubbles inside the skimmer's
body strip the water of undesirable
waste by-products
Protein Skimmer….How does this
happen? Surface tension.
Surface tension?
• The interaction between the oxygen bubble and
the surrounding water creates a kind of friction
between the two. This friction in turn "charges"
the molecules in the water.
• Playing on the old Physics Law of "opposites
attract", the charged gunk molecules "stick" to
the bubbles, riding them up the column of water.
Once the bubbles reach the surface air they
burst, depositing their hitchhikers into a
collection cup.
Plenum
• plenum is little more than a vacant space
in the substrate, harboring anaerobic
bacteria, which converts nitrates into
nitrogen
Plenum
• The original Jaubert filters included a deep
bed (4"-5") of live sand over the plenum,
which essentially seals off the plenum
from the oxygen rich water in the rest of
the tank. The upper level of the live sand
provides a home for the nitrifying bacteria,
which converts the generated ammonia
into nitrites, then nitrates, as well as a
home for all of the sand stirring critters
that keep the substrate clean.