Proteobacteria is the most diverse phylum of bacteria and is divided into three very different classes: Purple bacteria, Chemoautotrophic proteobacteria, and Chemoheterotrophic proteobacteria.

Purple Bacteria are photoautotrophs or photoheterotrophs who perform photosynthesis without releasing oxygen. They use non-water molecules such as H2S as a source for their electrons and bacteriochlorophylls and carotenoids in their plasma membranes as their energy harvesters.A flagella is sometimes present - Chromatium to the left is flagellated. They can be found in ponds, lakes, mudflats, and hot spring runoffs (see below).



Chemoautotrophic proteobacteria are a vital part of many ecosystems as many of them conduct nitrogen fixation (N2 to NO3 Nitrate). Plants use nitrate to assemble amino acids, and animals consume plants for their amino acids.Most plants and animals would perish if chemoautotrophic proteobacteria were to suddenly disappear - they are the key ingredient in the nitrogen cycle. Many live symbiotically with plants in their roots, and they can be found almost anywhere.

The black dots inside these vegetable roots
cells are thechemoautotrophic proteobacteria
Rhizobium. The bacteria takes over
"nodules" of the root.

Chemoheterotrophic proteobacteria are mainly endemic or intestinal bacteria. Most are rod-shaped, like E. Coli and Salmonella. E. Coli is a generally non-harmful bacteria that does have some damaging strains which can lead to hemorrhaging and contaminated hamburger patties. Salmonella is another very common pathogen that leads to “food poisoning.”

E. Coli