1. Proteobacteria Nitrogen-Fixing Bacteria
Earth's atmosphere is 80% nitrogen but plants and animals cannot use nitrogen in gaseous state
We require nitrogen to make nitrogen-containing compounds like proteins and nucleic acids
Rhizobium are essential to the nitrogen cycle
Legumes have lots of root nodules, filled with these bacteria

2. Cyanobacteria
Gram-Negative bacteria that perform plant-like photosynthesis & release oxygen as by-product (waste)
Once classified as blue-green algae
Now considered eubacteria, because they lack a membrane-bound nucleus & chloroplasts

3. Cyanobacteria
“Eutrophication”: Population Bloom of bacteria = sudden increase in # of cyanobacteria due to high availability of nutrients.
After many cyanobacteria die; decomposed by heterotrophic bacteria.
Consume available oxygen

4. Eutrophication