Solution

Photosynthetic bacteria are capable of entrapping solar energy and utilizing it for the synthesis of complex food materials due to the presence of pigments like bacteriochlorophyll (bacteriopurpurin) and bacterioviridin. Bacterial photosynthesis is also known as anoxygenic photosynthesis. In bacterial photosynthesis, water is not the source of electron that acts as reducing agent to convert $$CO_2$$ into glucose. The bacteria obtain reducing power from various compounds such as hydrogen sulphide, thiosulphate or even some organic compounds. No oxygen is evolved as it does not involve splitting of water. Hydrogen released by various compounds is picked up by $$NAD^+$$ which gets reduced to $$NADH_2$$ acting as reducing power. $$NADH_2$$ alongwith ATP, produced generally by entrapping solar energy are used to reduce $$CO_2$$ to glucose. The byproduct of bacterial photosynthesis is sulphur (S).