1. NITROGEN FIXATION 3 methods

2. 1.LIGHTENING a. high temps cause nitrogen & oxygen to for nitrogen monoxide b. this is oxidized by oxygen to form nitrogen dioxide c. NO2 + H2O form nitrate ions

3. 2. SYMBIOTIC-RHIZOBIUM a. roots of legumes are invaded by bacteria and form nodules on roots b. bacteria convert absorbed N2 in soil air into NH3 by reduction c. ATP & nitrogenase are needed d. NH3 reduced to NH4+ e. these are incorporated into a.a.

4. 3. Free-living Azotobacter a. Convert N2 in the soil air into NH3 by reduction b. Further reduced to NH4+ c. Moves into roots by active transport d. These are incorporated into a.a.

5. NITRIFICATION 2 METHODS

6. 1.Nitrosomonas a.oxidize NH3 to nitrites b. oxygen is required (aeration) 2.Nitrobacter a. oxidize NO2- to NO3- b. oxygen is required (aeration) c. NO3- enter roots by active transport d. plant reduces NO3- to NH4+ & then incorporated into a.a.

7. DENITRIFICATION 1.Pseudomonas denitrificans a. Convert NO3- to N2 b. Occurs under anaerobic conditions in waterlogged soil c. Use oxygen in NO3- as on O2 source for aerobic respiration d. Essential to maintain N2 in the atmosphere

8. MICROBIAL ROLES IN ECOSYSTEMS 1.PRODUCERS a. Breakdown dead organisms (plant & animal) b. Critical in N2 cycle & C cycle

9. 2. Nitrogen fixers a. Convert N2 gas into NO2- & NO3- as part of their metabolism b. Release products into environmemt c. Mostly in N2 cycle

10. 3. Decomposers a. Convert raw energy to organic molecules & nutrients for themselves and other organisms b. Varied group of bacteria, i.e. photosynthetic bacteria like cyanobacteria & chemosynthetic bacteria