Microbial nitrogen cycle

Question 1

Give four examples of sources of environmental nitrogen

Answer 1

Chemical reactions, bacterial N2 fixation, biodegradation, human activities

Question 2

What is the result of nitrogen release by human activities?

Answer 2

The release of nitrogen needs to be controlled because of intensity of release, the other sources are counterbalanced

Question 3

Give three examples if sources of organic nitrogen

Answer 3

Herb/pesticides, detritus, sewage sludge

Question 4

Is N2 fixation aerobic or anaerobic? What is the product?

Answer 4

Anaerobic
NH4^+

Question 5

What are the four components of the biological nitrogen cycle?

Answer 5

NH4^+ production
Nitrification
Denitrification
N2 fixation

Question 6

Describe NH4+ production

Answer 6

Bacterial urease from animal urea releases NH4^+
Plants release NH4^+ or org N (broken down into NH4^+) after taking up NO3^-
Xenobiotics are broken down slowly, releasing NH4^+

Question 7

Describe nitrification

Answer 7

Aerobic oxidation of NH4^+ to NO3-

Question 8

Describe denitrification

Answer 8

Anaerobic reduction of NO3^- to N2

Question 9

Describe N2 fixation

Answer 9

Anaerobic reduction of N2 to NH4^+

Question 10

What forms of nitrogen dominate the nitrogen cycle?

Answer 10

NH4^+, NO3^-, N2

Question 11

Where is NH4^+ desirable?

Answer 11

In soil for soil productivity
It must be added if the soil is deficient
Binds to anionic particles in soil

Question 12

What happens to NH4^+ in aerobic soils?

Answer 12

It is readily oxidised
Nitrification

Question 13

Where is NH4^+ undesirable?

Answer 13

Potable water
Can cause toxicity, mal odours, eutrophication

Question 14

Why can NO3^- be leached from soils?

Answer 14

Because it does not bind to anionic soil particles as easily as NH4+ does

Question 15

When can NO3^- be used by plants?

Answer 15

When it has been reduced before its assimilation into the amino acid pool

Question 16

Describe the organisms responsible for nitrification

Answer 16

Most are autotrophic chemolithotrophs
Very low growth rates/biomass yields

Question 17

Define chemolithotrophs

Answer 17

Obtain energy from redox reactions with an inorganic electron donor

Question 18

What is the role of heterotrophs in nitrification?

Answer 18

Their role is unclear

Question 19

What are the two steps in the reaction of nitrification?

Answer 19

NH4^+ oxidised to NO2^-
NO2^- oxidised to NO3^-

Question 20

What is the most abundant organism that oxidises NH4^+ to NO2^-?

Answer 20

Nitrosolobus

Question 21

What is the most studied organism that oxidises NO2^- to NO3^-?

Answer 21

Nitrobacter

Question 22

What is the second step nitrification catalysed by?

Answer 22

Nitrate oxidase

Question 23

What has been studied to show that ocean sites are critical in the global nitrogen cycle?

Answer 23

Ammonia monooxygenase

Question 24

What type of bacteria are typically associated with nitrification?

Answer 24

β- and γ-proteobacteria

Question 25

Define denitrification

Answer 25

The removal of nitrogen atoms from the pool of biologically active nitrogen used for growth

Question 26

What are the three types of microbial nitrate reduction?

Answer 26

Denitrification, nitrate assimilation, dissimilatory reduction of NO3^- to NH4^+ (reverse of nitrification)

Question 27

What are the key enzymes in denitrification?

Answer 27

Nitrate/nitrite reductase, nitric/nitrous oxide reductase

Question 28

Where is nitrate reductase found in the cell?

Answer 28

Cytoplasmic membrane

Question 29

Where is nitrite reductase found in the cell?

Answer 29

Periplasm

Question 30

What type of organisms cannot fix nitrogen?

Answer 30

Eukaryotes

Question 31

Describe free living nitrogen fixing bacteria

Answer 31

Can be obligate aerobes or anaerobes Can be photosynthetic Some methanogens and Fe(III)-reducers

Question 32

Describe nitrogenase

Answer 32

Used to fix N2

Question 33

What are the cofactors of nitrogenase?

Answer 33

Iron and molybdenum (Mo) (Their enzymes require ATP and reducing agents (NADH))

Question 34

What are the three steps of the general approach to treating N-containing wastes?

Answer 34

Denitrification plant (removes most org C and NO3^-), if resulting NH4^+ is high: nitrification plant (removes rest of C and NH4^+), if resulting NO3^- is high, repeat 1 and 2 until water is legal

Question 35

What is the legal N concentration in waste?

Answer 35

Treatment plants serving >100,000 people must achieve <10mg N per litre

Question 36

What did Broda (1977) suggest for waste water biotreatments?

Answer 36

Running denitrification and nitrification at the same time Using NH4^+ as e- donor for denitrification under anaerobic conditions

Question 37

What do anammox bacteria do?

Answer 37

Couple the oxidation of ammonium to nitrate reduction