Nitrogen Cycle Flashcards
Why is microbial involvement fundamental for nitrogen cycle?
- several key reactions are carried out exclusively in nature by microorganisms
What is the most stable type of bond?
triple
What would happen if there was no nitrogen cycle?
all nitrogen would be lost, give up free life
What is an environmental example of a nitrogen fixing bacteria?
pseudomonas
What happens when nitrates leach?
they grab nitrites and can enter atmosphere
Why is nitrogen needed by organisms?
- synthesis of proteins
- nucleic acids
What does a more valent nitrogen form mean?
more variety of transformation
What is a highly stable form of nitrogen? what is it used by?
N2, used by restricted group
Define nitrification
- conversion of ammonia to nitrate by nitrifying microorganisms (nitrate production)
Where does nitrification occur? Why?
Well drained soils at neutral pH
- oxygen is able to penetrate soil matrix
Define chemolithotroph
- chemo - energy source
- litho - inorganic forms of carbon
- gets energy from inorganic carbon
Where do chemolithotrophs get their energy from?
- oxidation of ammonia or nitrite
Why put manure in soil?
- fertilize it with organic material + encourage plant growth
What do plants require for growth? what do they not want?
- want ammonia in biologically useable forms
- don’t want nitrification
Why don’t plants want nitrification?
Deprives soil of ammonia needed
What form of nitrogen is used by plants in soil?
- Nitrate (No3)
What is the process that occurs with nitrate and ammonia in soil?
- NO3 and clay are neg charged and repel each other = nitrification and ends up in water to drive nitrogen out
- Ammonia charge is positive and attaches long enough for plants to use it
What happens if there is excess ammonia?
- bacteria will transfer to nitrites and nitrates causing leaching
Define denitrification
- conversion of nitrate to nitrous oxide or N2 by denitrifiers
- Nitrate consumption
What are the conditions during denitrification?
Anoxic (anaerobic)
What is used as the electron acceptor during denitrification?
NO3 rather than O2
What kind of anaerobes are denitrifiers and where are they found? Give an example.
facultative, perform in waterlogged soil
- pseudomonas
What kind of anaerobes are denitrifiers and where are they found? Give an example.
facultative, perform in waterlogged soil
- pseudomonas
Define ammonification
decomposition of organic nitrogen compounds to produce ammonia
What conditions is ammonia typically stable under?
- ANOXIC
What is the conversion during nitrogen fixation
nitrogen gas –> ammonia
What type of organism carries out nitrogen fixation
aerobic chemoorganotrophs
What is the major reservoir of nitrogen?
atmosphere
What does biological nitrogen fixation require?
nitrogenase
Define nitrogenase
- enzyme composed of 2 proteins: dinitrogenase and dinitrogenase reductase
What kind of protein is denitrogenase?
MoFe
What kind of protein is dinitrogenase reductase?
Fe
What is the electron flow in nitrogen fixation?
donor–> dinitrogenase reductase –> dinitrogenase –> N2 –> HN3
What are nif regulators? give an example.
genetic regulators
ex. kelbsiella pneumoniae
What are the 2 types of nitrogen-fixing organisms?
- nonsymbiotic
- symbiotic
Where are nonsymbiotic nitrogen-fixing bacteria found? give an example
- rhizosphere (free living)
- cyanobacteria
Define Rhizosphere
soil impacted by plant root
Define Rhizoplane
surface of root
What is a specific structure cyanobacteria has that protects nitrogenase from O2?
heterocyst
What is a specific structure cyanobacteria has that protects nitrogenase from O2?
heterocyst
What is a symbiotic nitrogen-fixing bacteria and what is an example?
- have own ammonia generators attached to root matrix
- ex. peanuts, soybean
What is a root nodulator?
- N-fixing bacteria that are breedable with plants
Define bacteroid
- bacteria like = no longer capable of free living life and becoming bacteria again
- once you reach certain point you cannot return
Steps in nodule formation
- recognition/attachment
- invasion of root hair
- travel via infection thread to main root
- formation of bacteroid
- continued division to form nodule
What is leghemoglobin and what does it do?
- O2 binding Fe protein
- controls O2 levels in root nodule
- found in healthy nodules
- oxygen buffer
What does leghemoglobin protect?
nitrogenase from O2
What is the ratio of O2 bound –> leghemoglobin TO free O2 in nodule?
10 000:1
What do bacteroids result from?
- rapid multiplication of bacteria in plant cells
What do bacteroids cause physiologically?
swelling
Define sybiosome
- bacteroid surrounded by portions of plant cell membrane
Where is nitrogenase localized?
in bacteroid
What happens to node and bacteroid when plant dies?
- released to surrounding soil: dormant cells can proliferate to initiate another infection
Can bacteroid forms divide?
No
what is symbiosome dependent on?
- plant for energy required for N2 fixation
When does dissimilatory nitrate reduction occur?
- as substitute for aerobic respiration when O2 levels are low
Why is N cycle naturally in balance?
N cycled between unusable N2 and usable NH3, NH4 ad NO3
What is the main result of assimilatory nitrate reduction?
- reduce nitrate to ammonia
- nitrate–>nitrite–>ammonia –> incorporated into organic carbon
