Photosynthesis - Anaerobic Photosynthetic Bacteria

This is a group of bacteria which do not produce oxygen during photosynthesis and only photosynthesize in environments which are anaerobic (lacking oxygen). All these bacteria use carbon dioxide and another oxidizable substrate, such as hydrogen sulfide, to make carbohydrates (see equation 2). These bacteria have bacteriochlorophylls and other photosynthetic pigments which are similar to the chlorophylls used by higher plants. Their photosynthesis is different from that of higher plants, algae and cyanobacteria in that they only have one photosystem. This photosystem is similar to PS-I. Most biologists believe that photosynthesis first evolved in anaerobic bacteria several billion years ago.