Purple non-sulfur bacteria

The purple non-sulfur bacteria are a family (Rhodospirillaceae) of phototrophic bacteria that photosynthesize using bacteriochlorophylls a and b in anoxic environments, such as the bottom mud of ponds and other stagnant water, although they are able to survive in air. The reducing agent involved is hydrogen rather than water, so oxygen is not produced.

Members of the family range in color from purple to red and brown, with shapes including spherical, rod, vibrio, and spiral (Rhodospirillum).

The genus Magnetospirillum is magnetotactic; using chains of tiny crystals of magnetite, these bacteria are able to use the Earth's magnetic field to return to the bottom of a pond (since the magnetic lines of force run downwards as well as to the north or south). Similar magnetite chains found in Martian meteorites have been suggested as evidence of life of Mars.