The Biogeochemical Cycles

Nitrogen Cycle

Nitrogen

Nitrogen-one of the most essential

elements-used to produce a number of

complex molecules like amino acids, nucleic acids

and lipids- covers 78% of the earth

atmosphere-cannot be used by most of

the living organisms until fixed

Amino acidsNH

4+

Ammonium

SYNTHESIS

AMMONIFICATION

Nitrogen

FIXATIONN

2AtmosphericNitrog

en

NH3Ammonia

Nitrogen Cycle

Nitrogen Cycle-the movement of nitrogen

between the earth and the atmosphere

-consists of a series of processes that convert nitrogen

gas to organic substances and these back to nitrogen in nature

- nitrogen cycle can be broken down into five types of reactions

Anammox

Reactions of Nitrogen Cycle

•Nitrogen fixation•Ammonification•Nitrification•Denitrification•Anammox

Nitrogen Fixation

Nitrogen Fixation

-reduction of atmospheric nitrogen to ammonia

-requires alot of energy to break the N2 bond

N2

AtmosphericNitrog

en

FIXATION

NH3Ammonia

Nitrogen Fixation

Ways to Fix Nitrogen1.Atmospheric Fixation- using

enormous energy of lightning to break nitrogen molecules

2.Industrial Fixation- use of atmospheric nitrogen and hydrogen as a catalyst under a great temperature(600°C)

3.Biological Fixation- fixation of nitrogen-fixing bacteria

Nitrogen Fixation

Nitrogen-Fixing Bacterias-contain an enzyme complex

called nitrogenase- use at least 16 ATP on each

N2

Nitrogenase-catalyst in the nitrogen-

fixation-it supplies oxygen and ATP -consists of two distinct

proteins, dinitrogenase and dinitrogenase reductase

Nitrogen Cycle

Free living Symbiotic with plants

Aerobic Anaerobic Legumes

Other plants

AzotobacterBeijerinckiaKlebsiella (s

ome)Cyanobacteria (some)*

Clostridium (some)

DesulfovibrioPurple sulphur

bacteria*Purple non-

sulphur bacteria*

Green sulphur

bacteria*

Rhizobium

FrankiaAzospiri

llum

Examples of nitrogen-fixing bacteria (*photosynthetic bacterium)

*Examples of nitrogen-fixing bacteria (*photosynthetic bacterium)

Red nitrogen-fixing nodules on the roots of a black alder tree. The nodules contain symbiotic Frankia sp. bacteria

Nodules on the roots of soybean plants containing Rhizobium sp. bacteria

Desulfovibrio vulgaris

Desulfovibrio sapovorans

Desulfovibrio desulfuricans

Ammonification

Ammonification-decomposition process that

converts organic nitrogen into ammonia (NH3) or ammonium in neutral environment

-performed by a large variety of organism, aerobes and anaerobes as well as fungi(decomposers)

Ammonification

Ammonification Process1. Initially done through the

action of extracellular proteolytic enzymes

2. The breakdown products goes into the cell

3. Release of ammonium

Streptomyces coelicolor colonies

Bacillus cereus colonies on sheep blood agar plate

Nitrification

Nitrification-oxidation of ammonia or ammonium to nitrate-done by a group of bacteria collectively known as nitrifiers-a cooperative two-step process

 

Nitrification

Nitrification Process1. Nitrosomonas (ammonia-

oxidizing bacteria), oxidizes ammonia to nitrite(Nitritation)

2. Nitrospira (nitrite-oxidizing bacteria) oxidizes nitrite to nitrate (Nitratation)

NITRITATION

NITRATATION

NH3Ammo

nia

NO2

-Nitrite

NO3

-Nitrate

Nitrosomonas sp. bacteriaUptake of Pyruvate by

Nitrosomonas(green) and Nitrospira(red). Taken via microautoradiography

Denitrification

Denitrification-conversion of nitrates into

primarily nitrogen gas but also nitrous oxide

-done by denitrifying bacteriasNO3

-Nitrate

N2

ONitrou

s Oxide

N2Atmospheric Nitrog

en

NITRITATION +

Denitrification

Environmental Consequences of Denitrification

-N2O can be photochemically oxidized to NO in the atmosphere. NO reacts with the ozone (O3) in the to form nitrite (NO2

-), and this returns to Earth as nitric acid (HNO2).

thinning of ozone layerformation of acid rain

Pseudomonas aeruginosa (XLD)Xylose lysine deoxycholate agar plate

Paracoccus denitrificans

Annamox

Annamox-oxidation of ammonium

under anaerobic conditions to form atmospheric nitrogen(N2)

-bacteria capable of this process possess a special membrane-bound organelle called annamoxosomes

NH4

+Ammonium

2H2

Owater

N2Atmospheric Nitrog

en

ANNAMOX ++N

O2-Nitrate

Groups of annamox bacteria

•Brocadia•Kuenenia•Anammoxoglobus• Jettenia (all fresh water species)

•Scalindua(marine species)

Reaction

Microorganism

Conditions

Process

Nitrogen fixation

Nitrogen-fixing bacteria e.g. Rhizobium

Aerobic/anaerobic

The first step in the synthesis of virtually all nitrogenous compounds. Nitrogen gas is fixed into forms other organisms can use.

Ammonification(decay)

Ammonifying bacteria (decomposers)

Aerobic/anaerobic

The decomposers, certain soil bacteria and fungi, break down proteins in dead organisms and animal wastes, releasing ammonium ions which can be converted to other nitrogen compounds.

Nitrification

Nitrifying bacteria (e.g. Nitrosomonas, Nitrobacter)

Aerobic Nitrification Nitrifying bacteria Aerobic Nitrification is a two-step process. Ammonia or ammonium ions are oxidized first to nitrites and then to nitrates, which is the form most usable by plants.

Denitrification

Denitrifying bacteria

Anaerobic

Nitrates are reduced to nitrogen gas, returning nitrogen to the air and completing the cycle.

Annamox

Bacterias with annamoxosomes

Anaerobic

Ammonium ions are oxidize to nitrogen gas, thus returning the nitrogen in the atmosphere

Anammox