Anoxygenic photosynthesis is unique to bacteria, but is found throughout the Bacterial Domain, particularly in groups like the purple non-sulfur bacteria. This is work done by the system. Thus, the electron transfer is considered to be cyclical. During electron transport, protons are pumped outside the cell by quinones, creating a proton motive force. It takes a lot of reducing power to reduce CO2.
Different bacteria generate reducing power in different ways.