How can rhodobacter possess a single 'PS-II' like reaction center?
McEwan (1994) Photosynthetic electron transport and anaerobic metabolism in purple non-sulfur phototrophic bacteria. Antonie Van Leeuwenhoek 66: 151-164.

...The purple non-sulfur bacteria ... carry out photosynthesis under anaerobic conditions. Photosynthetic electron transport is cyclic and involves ... two redox complexes ... reaction center (RC) [and] cytochrome bc1 complex. ... This cycle of electron transfer, [mediated
by ubiquinone (UQ) and a c-type cytochrome,] is linked to the generation of a proton motive force ... across the cytoplasmic membrane.