Meaning of purple bacteria

pur'ple bacte'ria

Pronunciation: [key]
  1. 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.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.