Domain Bacteria
Alpha Proteobacteria

The Alpha class includes most of the photosynthesizing species of the Proteobacteria.

They also include bacteria friendly to plants and animals as well as a group of dangerous pathogens.

The Alpha class has many orders. Among them:

• Rhizobiales are nitrogen-fixing bacteria crucial to plant growth.
• Rhodospirillales produce vinegar. Some navigate using earth's magnetic field. A newly-discovered pathogen (Granulobacter) is in this group.
• Rickettsiales are intracellular parasites in ticks, lice, fleas and mammals. They cause typhus fever and Rocky Mountain spotted fever.
• Parvularculales are marine bacteria living in floating seaweed.

Most importantly for us, the precursors of mitochondria (which allow eukaryotic cells to metabolize energy) are thought to have originated in this bacterial group.