Microbial nitrogen cycle Flashcards
Give four examples of sources of environmental nitrogen
Chemical reactions, bacterial N2 fixation, biodegradation, human activities
What is the result of nitrogen release by human activities?
The release of nitrogen needs to be controlled because of intensity of release, the other sources are counterbalanced
Give three examples if sources of organic nitrogen
Herb/pesticides, detritus, sewage sludge
Is N2 fixation aerobic or anaerobic? What is the product?
Anaerobic
NH4^+
What are the four components of the biological nitrogen cycle?
NH4^+ production
Nitrification
Denitrification
N2 fixation
Describe NH4+ production
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^+
Describe nitrification
Aerobic oxidation of NH4^+ to NO3-
Describe denitrification
Anaerobic reduction of NO3^- to N2
Describe N2 fixation
Anaerobic reduction of N2 to NH4^+
What forms of nitrogen dominate the nitrogen cycle?
NH4^+, NO3^-, N2
Where is NH4^+ desirable?
In soil for soil productivity
It must be added if the soil is deficient
Binds to anionic particles in soil
What happens to NH4^+ in aerobic soils?
It is readily oxidised
Nitrification
Where is NH4^+ undesirable?
Potable water
Can cause toxicity, mal odours, eutrophication
Why can NO3^- be leached from soils?
Because it does not bind to anionic soil particles as easily as NH4+ does
When can NO3^- be used by plants?
When it has been reduced before its assimilation into the amino acid pool
Describe the organisms responsible for nitrification
Most are autotrophic chemolithotrophs
Very low growth rates/biomass yields
Define chemolithotrophs
Obtain energy from redox reactions with an inorganic electron donor
What is the role of heterotrophs in nitrification?
Their role is unclear
What are the two steps in the reaction of nitrification?
NH4^+ oxidised to NO2^-
NO2^- oxidised to NO3^-
What is the most abundant organism that oxidises NH4^+ to NO2^-?
Nitrosolobus
What is the most studied organism that oxidises NO2^- to NO3^-?
Nitrobacter
What is the second step nitrification catalysed by?
Nitrate oxidase
What has been studied to show that ocean sites are critical in the global nitrogen cycle?
Ammonia monooxygenase
What type of bacteria are typically associated with nitrification?
β- and γ-proteobacteria
Define denitrification
The removal of nitrogen atoms from the pool of biologically active nitrogen used for growth
What are the three types of microbial nitrate reduction?
Denitrification, nitrate assimilation, dissimilatory reduction of NO3^- to NH4^+ (reverse of nitrification)
What are the key enzymes in denitrification?
Nitrate/nitrite reductase, nitric/nitrous oxide reductase
Where is nitrate reductase found in the cell?
Cytoplasmic membrane
Where is nitrite reductase found in the cell?
Periplasm
What type of organisms cannot fix nitrogen?
Eukaryotes
Describe free living nitrogen fixing bacteria
Can be obligate aerobes or anaerobes
Can be photosynthetic
Some methanogens and Fe(III)-reducers
Describe nitrogenase
Used to fix N2
What are the cofactors of nitrogenase?
Iron and molybdenum (Mo)
(Their enzymes require ATP and reducing agents (NADH))
What are the three steps of the general approach to treating N-containing wastes?
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
What is the legal N concentration in waste?
Treatment plants serving >100,000 people must achieve <10mg N per litre
What did Broda (1977) suggest for waste water biotreatments?
Running denitrification and nitrification at the same time
Using NH4^+ as e- donor for denitrification under anaerobic conditions
What do anammox bacteria do?
Couple the oxidation of ammonium to nitrate reduction
