In recent times, the photosynthetic microorganisms are receiving increasing attention in view of their anaerobic autotrophic nature and diverse metabolism. They have immense potential of biosynthetic and biodegradative activity in addition to having capacity of 100% hydrogen production ability under aerobic and anaerobic conditions.. Further, they can exist both under dark and light. In view of their specialized ecological niche, they need special conditions for their growth. Inspite of their uniqueness, they have been little studied. PNSB physiology, production of metabolites, production of industrial enzymes, and production of hydrogen under different conditions are critically nalysed. A water pollution remediation anoxygenic phototropic purple non sulphur bacterium is also included in this part. The genetic transformation of the bacteria for possible application in enhancing their metabolite production, biofuel production and bioremediation capabilities under different environmental conditions is also discussed.