N S cycling Flashcards
Nitrogen Cycle
atmosphere is major resevoir (80% N2), N2 is fixated by prokaryotes, lots of recycling in terrestrial and aquatic enviornments, N is lost back into the atmosphere by denitrification
Nitrogen redox cycle
denitrification is carried out by facultative aerobes
- Nitrification: Ammonia (NH3) to Nitrite (NO2) to nitrate (NO3)
- denitrification: Nitrate to atmospheric N2
- N2 fixation: N2 to ammonia (NH3)
- anmonification: organic N to ammonia
- anammox: Nitrite and ammonia to atmospheric N2
Nitrogen fixation
nitrogenase complex is O2 sensitive
FeMo cofactor is site of reduction
-overall reaction: N2 + 8H+ + 8e- → 2NH3 + H2
symbiotic (mutualisms) nitrogen fixing
legumes-rhizhobia symbioses, actinorhizal plants with actinobacteria
Free living an/aerobes nitrogen fixing
chemoorganotrophs , phototrophs including cyanbacteria, chemolithotrophs
Protecting nitrogenase from inactivation
stabilizing proteins, heterocysts, leghemoglobin
Heterocysts
modified cells found in certain filamentous cyanobacteria
-lack photosystem II (& thus do not produce O2), but possess nitrogenase & can conduct N2 fixation
Symbiotic N2 fixation
1) bacterium attaches to hair root
2) root hair curls around bacterium
3) infection thread forms and bacteria replicate
4) thread extends into root cortex as root cells divide
5) bacteria enters cells and loses cell walls, become N2-fixing bacteriods
6) nodule grows due to bacteroids
Flavonoids
attract rhizobia to induce nod factor synthesis which control hair curling
bacteriods
rhizobial cells transformed into swollen, misshaped brannched shaped within plant cell, process nitrogenase activity, incapable of cell division
symbiosome
: bacteroids surrounded by portions of plant cell membrane; N2-fixation begins after symbiosome formation
leghemoglobin
O2-binding protein; supplies O2 to the bacteroid and protects nitrogenase from O2-inactivation
synthesis requires input from the plant and the bacterium
Ammonification
produce ammonia during decomposition by an/aerobes
- in oxic conditions: some NH3 volatilizataion to the atmosphere, assimilation to produce more biomass, NH4 undergoes nitrification
- in anoxic conditions: NH4 is stable except for when anammox occurs (anoxic ammonia conditins)
Nitrification
occurs in neutral pH soils&aquatic environments, aerobic, chemolithotrophic, eg. nitrosomonas and nitrospira
- ammonia oxidizing archaea
- comammox: oxidizes ammonia to nitrate itself
anammox
phylum: planctomycetes
- anaerobic chemolithoautotrophs, oxidize ammonia using nitrite as an e- acceptor produce N2
- occurs where an/oxic environments are together
- accounts for 1/2 of N loss in marine environements
- in wastewater treatments is controlled by [O2]
