The genus *Rhodospirillium* are bacteria that fix nitrogen. This means they use nitrogen for their metabolism. 

Purple non-sulfur bacteria, *Rhodospirillium*

This type of purple bacteria can use hydrogen for oxidation.

University of Wisconsin - Madison

Phototrophic purple and green bacteria can be classified into four main groups based on their ability to use sulfur compounds for oxidation: purple sulfur bacteria, purple non-sulfur bacteria, green sulfur bacteria, and green non-sulfur bacteria.

Classification of Purple and Green Bacteria

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This type of purple bacteria can oxidize hydrogen sulfide (H<sub>2</sub>S).

Purple Sulfur Bacteria *Chromatium*

Purple non-sulfur bacteria 

Green sulfur bacteria use sulfide (S<sup>2-</sup>) for an oxidation reaction to make green bacteriochlorophyll.  

Green sulfur bacteria

Green non-sulfur bacteria use other compounds for oxidation such as hydrogen.

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