Question

Does photosynthesis occur in bacteria? If yes, then how?

Answer 1

Photosynthesis is the conversion of light energy(photons) into chemical energy in the form of ATP. Prokaryotes which will convert light energy into energy include the photosynthetic cyanobacteria, the purple and green bacteria, halobacteria etc.
Net equation: $6C{{O}_{2}}\text{ }+12{{H}_{2}}O+LightEnergy\text{ }\to {{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{O}_{2}}+6{{H}_{2}}O$
These Photosynthetic bacteria contain light absorbing pigments and reaction centres which are capable of converting light energy into chemical energy. Photosynthetic pigments: Bacteriochlorophyll, carotenoids, bacteriorhodopsin, phycobilins.

Complete answer:
Yes, photosynthesis occurs in some bacteria, e.g. purple and green-sulphur bacteria and cyanobacteria. Photosynthetic pigments are present within the membrane infoldings of bacteria as they lack chloroplasts. Cyanobacteria or cyanobacteria contain chlorophyll and may perform oxygenic photosynthesis like plants. Other bacteria perform anoxygenic photosynthesis and don't evolve ${{O}_{2}}$ like plants. They need bacteriochlorophyll and utilize ${{H}_{2}}S$ and other compounds as reducing agents.
In Oxygenic photosynthetic bacteria the photosynthesis occurs in lamellae which house thylakoids containing chlorophyll a/b and phycobilisomes pigments to collect light energy. This process involves two photo systems (PS): PS II- which generates a proton-motive force for creating ATP whereas, PS I-generates low potential electrons for reducing power.
Whereas in Anoxygenic photosynthetic bacteria, the bacteria consume $C{{O}_{2}}$, light energy to make organic compounds, sulfur or fumarate compounds rather than${{O}_{2}}$. It occurs in green thiobacteria, phototrophic bacteria, green gliding bacteria, Filamentous Anoxygenic Phototrophs (FAPs), Phototrophic Acidobacteria, and Phototrophic Heliobacteria. It uses bacteriochlorophyll (photosynthetic pigment) rather than chlorophyll and involves one photosystem (PS I) to get ATP in “cyclic” manner.

Note:
Cyanobacteria are the most important and most diverse group of photosynthetic bacteria previously referred to as blue chlorophyte. These are known to be true prokaryotes, having no chloroplast but still perform photosynthesis. The reason for this is often that they need chlorophylls which are dispersed in cytoplasm (not packed in chloroplasts like photosynthetic eukaryotes). They perform oxygenic photosynthesis i.e., they use water as an electron donor and generate oxygen during photosynthesis. Their photosynthetic systems closely resemble those of eukaryotes: These bacteria use Phycobilins as accessory pigments. Electron transport chain(ETC) components and photosynthetic pigments are located in thylakoid membranes linked with particles called Phycobilisomes. Phycocyanin(blue) pigment is their predominant phycobilin. $C{{O}_{2}}$ in these bacteria is consumed and used through the Calvin cycle.