Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria (Chromatiales, in part) and purple non-sulfur bacteria. Purple bacteria are anoxygenic phototrophs widely spread in nature, but especially in aquatic environments, where there are anoxic conditions that favor the synthesis of their pigments.
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In this Dossier
- ⭐ Core Definition: Purple nonsulfur bacteria
- Purple nonsulfur bacteria in the context of Rhodospirillaceae
Purple nonsulfur bacteria in the context of Rhodospirillaceae
The Rhodospirillaceae are a family of bacteria within the Pseudomonadota. The family is metabolically diverse, though it is known for its purple nonsulfur bacteria, which produce energy through photosynthesis. Originally, all purple nonsulfur bacteria were classified in this family.
Members of this family are often found in anaerobic aquatic environments, such as mud and stagnant water, though they are capable of surviving in the presence of air. A notable genus, Magnetospirillum, exhibits magnetotaxis. These bacteria contain internal chains of magnetite that allow them to orient themselves along the Earth's magnetic field lines, aiding their movement toward the sediment of ponds where they live. The discovery of similar magnetite structures in Martian meteorites has led to speculation about the possibility of ancient life on Mars.
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