| a group of Gram-negative pink to purplish-brown bacteria, comprising the purple sulfur bacteria and purple nonsulfur bacteria, that occur in anaerobic aquatic environments and carry out a unique form of photosynthesis without oxygen, using the pigment bacteriochlorophyll. |
| purple bacteria | |
noun | |
| free-living Gram-negative pink to purplish-brown bacteria containing bacteriochlorophyll |