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EART21102 Environmental Microbiology > Microbial nitrogen cycle > Flashcards

Microbial nitrogen cycle Flashcards

1
Q

Give four examples of sources of environmental nitrogen

A

Chemical reactions, bacterial N2 fixation, biodegradation, human activities

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2
Q

What is the result of nitrogen release by human activities?

A

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

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3
Q

Give three examples if sources of organic nitrogen

A

Herb/pesticides, detritus, sewage sludge

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4
Q

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

A

Anaerobic
NH4^+

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5
Q

What are the four components of the biological nitrogen cycle?

A

NH4^+ production
Nitrification
Denitrification
N2 fixation

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6
Q

Describe NH4+ production

A

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^+

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7
Q

Describe nitrification

A

Aerobic oxidation of NH4^+ to NO3-

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8
Q

Describe denitrification

A

Anaerobic reduction of NO3^- to N2

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9
Q

Describe N2 fixation

A

Anaerobic reduction of N2 to NH4^+

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10
Q

What forms of nitrogen dominate the nitrogen cycle?

A

NH4^+, NO3^-, N2

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11
Q

Where is NH4^+ desirable?

A

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

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12
Q

What happens to NH4^+ in aerobic soils?

A

It is readily oxidised
Nitrification

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13
Q

Where is NH4^+ undesirable?

A

Potable water
Can cause toxicity, mal odours, eutrophication

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14
Q

Why can NO3^- be leached from soils?

A

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

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15
Q

When can NO3^- be used by plants?

A

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

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16
Q

Describe the organisms responsible for nitrification

A

Most are autotrophic chemolithotrophs
Very low growth rates/biomass yields

17
Q

Define chemolithotrophs

A

Obtain energy from redox reactions with an inorganic electron donor

18
Q

What is the role of heterotrophs in nitrification?

A

Their role is unclear

19
Q

What are the two steps in the reaction of nitrification?

A

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

20
Q

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

A

Nitrosolobus

21
Q

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

A

Nitrobacter

22
Q

What is the second step nitrification catalysed by?

A

Nitrate oxidase

23
Q

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

A

Ammonia monooxygenase

24
Q

What type of bacteria are typically associated with nitrification?

A

β- and γ-proteobacteria

25
Q

Define denitrification

A

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

26
Q

What are the three types of microbial nitrate reduction?

A

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

27
Q

What are the key enzymes in denitrification?

A

Nitrate/nitrite reductase, nitric/nitrous oxide reductase

28
Q

Where is nitrate reductase found in the cell?

A

Cytoplasmic membrane

29
Q

Where is nitrite reductase found in the cell?

A

Periplasm

30
Q

What type of organisms cannot fix nitrogen?

A

Eukaryotes

31
Q

Describe free living nitrogen fixing bacteria

A

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

32
Q

Describe nitrogenase

A

Used to fix N2

33
Q

What are the cofactors of nitrogenase?

A

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

34
Q

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

A

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

35
Q

What is the legal N concentration in waste?

A

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

36
Q

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

A

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

37
Q

What do anammox bacteria do?

A

Couple the oxidation of ammonium to nitrate reduction

EART21102 Environmental Microbiology (9 decks)

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