Organotrophs

A. Phototrophs: the bacteria which use light energy as a source of energy are known as photo-Autotrophs. It is of two types
1. Green sulphur bacteria 2. Purple Sulphur bacteria
1. Green sulphur bacteria: these are small nonmotile, rod-shaped bacteria that are anaerobic photoautotrophs. they contain a pigment called Chlorobium chlorophyll also known as Bacterioviridin that is responsible for absorbing light energy. these bacteria use H2S or other reduced inorganic sulphur compounds as electron donors.e,g Chlorobium, etc
2. Purple Sulphur bacteria: These are also autotrophs and their photosynthetic pigments are bacteriochlorophyll a or b. e,g Thiospirillum, and Amoebobacter.